training manual photoelectric sensors - ifm.com · earlier sensor generations such as interference...

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Training manual

Photoelectric sensors

Training manual

Training manual photoelectric sensors (as in March 2003)\\DEESNW01\VE\VTD\DATEN\STV\INTERN\Sc- und Se-Unterlagen alt\ENGLISCH\SC\SC200\Sc200e.doc 17.01.07 09:34

Note on guarantee

Utmost care was taken when writing this manual. Nevertheless, we cannot guarantee that the contents are correct.

Since it is impossible to avoid mistakes despite intensive efforts, we always appreciate indications.

We reserve the right to make technical alterations concerning the products so that deviations from the contents of thetraining manual may result.

For further information, data sheets, prices, etc. please go to www.ifm-electronic.com


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Contents

1 Introduction 6

1.1 Photoelectric sensors in industrial applications 6

1.2 Notation 8

1.3 On the contents 8

2 Light 10

2.1 Electromagnetic waves 10

2.1.1 Nature of the light 10

2.1.2 Ranges of wave length 12

2.1.3 Origin of light 15

2.1.4 Radiation spectrum 18

2.2 Radiation and temperature 21

2.2.1 Black emitters 21

2.2.2 Emission 21

2.2.3 Reflection and colour 22

2.3 Laser 24

2.3.1 Meaning 24

2.3.2 Features 25

2.3.3 Terms 27

2.3.4 Laser sensors 28

2.4 Refraction 29

3 Characteristics of photoelectric sensors 32

3.1 Comparison with other types of sensors 32

3.1.1 Definition 32

3.1.2 Immunity to interference of different sensor types 33

3.1.3 Ranges of sensor systems 33

3.2 Through-beam sensors 34

3.2.1 Operating principle 34

3.2.2 Information on the use of through-beam sensors in practice 38

3.3 The retro-reflective sensor 43


3.3.2 Use of retro-reflective sensors in practice 483.3.2.1 Sensors with polarisation filter 48

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3.3.2.2 Laser units and prismatic reflectors 503.3.2.3 Prismatic reflector 513.3.2.4 Summary 53

3.4 Diffuse reflection sensors 54


3.4.2 Notes on the use of diffuse reflection sensors in practice 563.4.2.1 Range 563.4.2.2 Setting 583.4.2.3 Background suppression 603.4.2.4 Summary 64

3.4.3 Units with special features 65

3.5 Fibre optics 67

3.5.1 Typical applications 67


3.5.3 Notes on the use of fibre optics in practice 71

3.6 Light-on and dark-on mode 73

3.7 Excess gain 76

3.7.1 Meaning 76

3.7.2 Setting 78

3.8 Switching frequency 80

4 Examples of photoelectric sensors 83

4.1 Technology 83

4.1.1 Circuitry 83

4.1.2 Operational reliability and failure warning 85

4.2 Current and voltage ranges 91

4.2.1 Leakage current, minimum load current and voltage drop 92

4.2.2 Connection 92

4.3 Handling 97

4.3.1 Setting of the sensing range 974.3.1.1 OG as through-beam sensor 984.3.1.2 OG as retro-reflective sensor 984.3.1.3 OG as diffuse reflection sensor 1004.3.1.4 OGH as diffuse reflection sensor with background suppression 1024.3.1.5 Displays and other settings 102

4.3.2 Timers 106

4.4 Mechanical properties 112

4.4.1 Designs and ranges 112

4.4.2 Mounting 112

4.4.3 Lens attachment 122


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4.5 Overview 122

4.6 Units with special properties 125

4.6.1 Side or front lens 125

4.6.2 Separate amplifier 125

4.6.3 Contrast sensor 127

4.6.4 Colour sensor 128

5 Infrared sensors 131

5.1 Operating principle 131

5.1.1 Radiation 131

5.1.2 Degree of emission 132

5.1.3 Technology 133

5.2 Information on practical use 135

5.2.1 Angle of aperture 135

5.2.2 Setting instructions for OWI 139

5.2.3 Operating conditions 140

6 Applications 143

6.1 Photoelectric sensors 143

6.1.1 Recommended sensor types 143

6.1.2 Application examples 144

6.2 Infrared sensors 150

Annex 159

Type keys 159

Production code 163

Table degree of emission 164

Table range on prismatic reflectors 166

Glossary of technical terms 171

Index 175

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1 Introduction

1.1 Photoelectric sensors in industrial applications

What are they used for? Photoelectric sensors have become indispensable components in almostall automated production processes.

Photoelectric sensors are used for safe and fast detection, positioning andcounting of parts.

We would like to start with one example of the variety of applications.Other applications can be found below (see e.g. 6.1.2).

Figure 1: edge and sag monitoring

What is monitored here? The example shows the variety of applications. The sensors monitorwhether the material is transported in a straight line and whether the sizeof the sag is sufficient. This sag functions as a buffer so that the materialdoes not tear if the process is disturbed or in case of a sudden stop. Thisapplication exists in many industries:� paper production¡ paper processing (printing house, packing industry)¡ plastic processing (production of carrier bags)¡ textile industry etc.

Photoelectric sensors have the largest market share of the binary positionsensors. As a tendency the market will increase. Market increases ofapprox. 8 to 9% a year are forecasted.


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ExamplesType Accessories Market segment

OF --- packing industryOBF fibre optics packing industry and automationOG angle brackets packing industry; food industryOL angle brackets with

protective covermaterials handling

OJ mounting components food industry

Modern photoelectric sensors offer a precise lens and intelligentelectronics as a standard. Both components are integrated in robusthousings made of resistant plastic or metal. The technical problems ofearlier sensor generations such as interference by extraneous light orshort cleaning and maintenance intervals have almost been solved today.

Three fundamental physical principles with several subgroups provide asolution to many different problems in different applications. The correctselection of the fundamental principle and of the type is very importantfor safe functioning. The sensing range is one main criterion for theselection of the correct sensor (see 3.1).

The present and the future

Easy handling and reliability There is a current trend towards more intelligence in the sensor (e. g. see3.4.2). In future there will hardly be a photoelectric sensor withoutmicroprocessor. This will lead to easier use, especially setting, as well asincreased operational reliability.

Mechanics Another trend that also applies to other sensor types is that usefulaccessories can increase the user's benefit. In this case angle bracketsthat protect the sensor against mechanical damage in ruggedapplications and mounting accessories that make alignment andadjustment easier are offered. This becomes more and more importantsince the sensors are increasingly compact by the use of microprocessorsand the development of other components. Sensors with comparable orimproved characteristics have only a fraction of the volume of the unitsdeveloped in the past.

Special applications Robust angle brackets enable the use of sensors such as OL in conveyorsystems. Other sensors have special optical features for specialapplications, e.g. colour sensors, contrast sensors or laser units. For abetter understanding of the functioning and the characteristics, thechapter about the fundamental principles of optical sensing wasextended considerably.

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1.2 Notation

The notation is explained here to make it easier to read the text and tofind information.

Headwords Headwords are indicated at the left margin. They give information on thetopic in the following paragraph.

What does FAQ mean? It means Frequently Asked Questions. This term is often used for modernelectronic media. Almost every beginner of a new topic has the samequestions. Sometimes they can be found at the beginning of a paragraphinstead of a headword. They are written in italics to distinguish themfrom simple headwords.

( 4) A number in round brackets at the left margin indicates a formula that isreferred to later in the text, e.g. see ( 4). Of course these formulas neednot be learned by heart. They are to facilitate the understanding of thematter because like a figure a formula describes the context in a shorterand clearer way than many words.

1.3 On the contents

This manual describes the principles of the photoelectric sensors.Important terms and correlations are explained, state-of-the-arttechnology is described and technical data of the units are given. Thisresults in the following structure.

1. Introduction This introduction is followed by the chapter:

2. Light This chapter contains a short description of the physical principles whichare useful for a better understanding of the functioning and thecharacteristics especially of laser and infrared units. Some basic terms andtheir correlation are described.

3. Characteristics of the photoelectric sensorsCharacteristics of binary sensors are discussed. Other more complexsystems that are also used in practice are mentioned. A general overviewof the different sensor systems follows. Among others, this is to facilitatea correct classification of photoelectric sensors as well as the decisionwhere they can be used and where not. Afterwards the three sensorversions and their specific features are presented. The knowledge ofthese features, the advantages and disadvantages, is a prerequisite for auseful discussion with users.

4. Examples of units In this chapter the data of sensors are given and explained. Themechanical structure, the optical and electrical characteristics, the useand the setting of the range are described here. In addition someapplications are presented.


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Annex This manual is also meant for your own studies. Terms that are lessfrequently used are explained in a short technical glossary. The pointsthat are essential for the photoelectric sensor are explained in details inthe preceding chapters. The index helps to look up a topic. The glossarycontains another short explanation of important terms. The type key andthe code for the production date are also presented briefly.

Much success! On the basis of this manual everyone should be able to make use of theopportunity provided by photoelectric sensors and successfully implementthem.

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2 Light

Is it necessary to know this? In this chapter the physical principles are described briefly. If you knowthis or remember what you have once learnt about it, the understandingof the operating principle and the overview of the sensor types and theiruse is easier. Knowledge of the principles is important especially tounderstand how a laser unit works. Of course, you can also use such aunit without knowing what a laser is. But basic knowledge is necessary tobe a competent partner in discussions. The following information allowsa better understanding of the special features of the infrared sensors.

This presentation shall however not be too extensive or theoretical. Wetry to concentrate on essential information. This requires shortening andsimplification.

2.1 Electromagnetic waves

2.1.1 Nature of the light

What is light? For a long time experts argued about the question what light really is.Some people, such as Newton, were of the opinion that light consists ofsmall particles, the photons. This is how today we image electrons forexample.

Wave? The other opinion was that light is a wave that has characteristics similarto a water wave. Many experiments the results of which can only beexplained by interference have strengthened this opinion. Interferenceresults from a superposition of waves (see Figure 2). If the crest of a wavemeets the hollow of a wave, the light intensity is 0. If however a crestmeets a crest or a hollow meets a hollow, the wave is intensified. (pleasealso see the term "granular" in 2.3.2).

Duality Modern physics, quantum physics, among others based on Einstein'sideas, found a solution worthy of a Solomon at the beginning of the 20thcentury. The question: "wave or particle?" is answered by: "it depends"or "both". This concept that is called duality cannot be explained in moredetail here. It is only mentioned to explain that it is no contradiction touse the one or the other aspect as an explanation of a phenomenon.

Interpretation A short comment on this: physics is a so-called "exact" science. This isoften interpreted as a rigid system of everlasting truths expressed byformulas that are difficult to understand. This has a deterrent effect onmany people. It is not considered that in physics there are also heateddiscussions about "interpretations" that we normally know fromtheology. This shows that it can also be exciting to deal with suchprinciples.


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Danger ! To understand the danger of radiation for human beings the followingtwo aspects have to be taken into account. There may be two differenttypes of danger.

¡ Intensity

If you focus for example the light of the sun in a burning glass, contactwith the skin can result in burns. If laser light is focussed (the human eyealso has a lens!) this can also lead to damage (see 2.3.2). The completequantity of energy per surface is decisive here. Other characteristics suchas the wave length are not important here.

¡ Wave length

This depends on the energy of the light particles. The shorter the wavelength, the higher the energy. For this reason ultraviolet radiation isdangerous for us. Figure 11 shows that the sun emits most of the light inthe visible range. Nevertheless the share of the ultraviolet range isenough to cause a sunburn.

Wave length and frequency Let us go into waves first. Waves are characterised by wave length andfrequency. In view of the correlation between the two quantities, it ismostly enough to consider only one of these quantities. In the followingtext only the wave length will be considered. The correlation is verysimple in a vacuum. In other media, such as glass, it can be morecomplicated (dispersion). For applications with photoelectric sensors thisis however only important in rare cases. Since air has almost the sameeffect on light as vacuum, this simple correlation can be used:

( 1) c = * f

c = 3 * 109 m/s: light velocity

[m]: wave lengthf [1/s]: frequency

For visible light the typical wave length is for example:500 * 10-9 m (see 2.1.2).

The frequency results from ( 1):0.6 * 1016 Hz.

This is so high above the MegaHz (109 Hz) and even the GigaHz range(1012 Hz) that interference of photoelectric sensors by such waves ofcomparably low frequency, such as by radio, can be excluded. The onlysource of interference is extraneous light (see table "Influence ofinterfering factors on different sensor types" in 3.1.2). The aspect thatthese are electromagnetic waves need not be considered here. Strictlyspeaking this applies to the area in front of the sensor. The electronicscan be influenced just like that of other types of sensors. The topic ofEMC is discussed in the training manual CE marking.

What does the wave look like? With regard to photoelectric sensors it is important that these waves aretransverse waves. This means that the oscillation (here of the electric andmagnetic fields) is vertical to the direction of propagation. A plane that isdefined by two directions is vertical to the direction of propagation that

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can be imagined as a straight line. The statement "vertical to thedirection of propagation" is thus ambiguous. There are two possibilities,e.g. "upwards" or "to the side".

Polarisation Normally light has no preferred direction of oscillation. If the direction ishowever limited to one single direction by a filter, this is called polarisedlight. The plane defined by the direction of oscillation and the direction ofpropagation is called polarisation plane (see 3.3.2, Figure 46 and Figure47). Polarised light is especially used for one type of retro-reflectivesensor (see 3.3).

A classification into different ranges of wave length is called spectrum.

2.1.2 Ranges of wave length

Electromagnetic waves exist within a wide range. The only differencebetween radio waves, visible light, X-rays etc. is their wave length.

Wave length Figure 2 shows the wave length that is called in most cases.

Figure 2: wave length

The light which photocells require for the detection of an object consistsof wave lengths within the range of electromagnetic radiation betweenapprox. 1 mm and 10 nm. Within this range a distinction is madebetween UV light (ultraviolet), light visible for the human eye and IR light(infrared).


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Figure 3: electromagnetic radiation spectrum

The upper part of Figure 3 shows the range that is of interest here. Thefollowing table defines the range in more details.

Wave length range Radiation designation100 nm - 280 nm280 nm - 315 nm315 nm - 380 nm380 nm - 440 nm440 nm - 495 nm495 nm - 558 nm558 nm - 640 nm640 nm - 750 nm

750 nm - 1400 nm1.4 µm - 3,0 µm3.0 µm - 1000 µm

UV - CUV - BUV - A

light - violetlight - blue

light - greenlight - yellow

light - redIR - AIR - BIR -C

classification of the radiation spectrum to DIN 5031

The transitions between the individual ranges and the individual coloursof the visible light are continuous (cf. rainbow). The topic "colour" that isimportant for one special sensor will be discussed in detail in 2.2.3.

Most units use infrared light with the wave length = 880 nm astransmitted light. But in some particular cases red light with a wavelength of = 660 nm and infrared light with = 950 nm are used. Thelaser diode emits red light with a wave length of = 675 nm (cf. Figure14). Moreover, there is a current trend towards red light, see below.

Infrared light The infrared light has several positive characteristics. It is among othersused to make units as resistant to external interference as possible.¡ The receiver transistor in use (a diode for types OI and OP) has its

maximum sensitivity in the infrared range, see Figure 14.¡ The transmitter diodes for infrared light have a higher efficiency that

is they emit more radiation when the same current is applied.¡ This utilises the effect that light with a wave length longer than the

diameter of very small dust particles passes such particles almost

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without any problems at all (diffraction). This is why radiation at verylong wave lengths (IR and not UV) is used to provide protectionagainst soiling and dust, see Figure 4 and Figure 5.

¡ The units are less susceptible to extraneous light sources of the visiblerange by the use of infrared light.

¡ The light spot is not visible which makes installation and adjustmentmore difficult.

Diffraction The correlation between the size of the object, the wave length and theterm diffraction is explained briefly. We know from the so-calledgeometrical optics that parallel light that strikes the object casts ashadow, the edge of which is parallel to the direction of the light (Figure4).

Figure 4: cast shadow

When the receiver is behind the object, no light can strike it. If the objectis smaller than the receiver, it is partly covered. If many small objects (dustparticles) are in front of the receiver, this can lead to the receiversignalling "light beam interrupted". In this case this is a failure.

Malfunctioning due to soiling by dust is a typical problem forphotoelectric sensors (also see excess gain in 3.7).

If the object has almost the same size as the wave length (approx. 800nm, see above), the phenomenon of diffraction can be observed. Thelight can "go around the object".

light object shadow

Figure 5: diffraction

This means that the receiver can no longer be covered so easily.

light object shadow


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Most objects which are normally used are much bigger than the wavelength so that the principles of geometrical optics can be applied. But forfine dust or mist a longer wave length is advantageous to reduce failurescaused by dust.

Is this diffuse? This must not be confused with a diffuse shadow we often see e.g. incase of sunlight. This is due to the fact that it is no point source of light.This is for example also the case for several light sources. In this contextthis effect is however not important.

Red light In view of the advantages of the infrared light listed above this light isused for most sensors. It must however be expected that the continuingdevelopment and improvement of red light diodes will lead to anincreasing use of these diodes which are easier to install and adjust. Inaddition there are other reasons to use red light. Summary:¡ polarisation filters (see 3.3.2) for red light are better and less expensive.¡ the attenuation in fibre optics (see 3.5) is smaller for red light.¡ the light spot is visible, which makes installation and adjustment easier

2.1.3 Origin of light

Where do the small light waves come from?The term "wave length" that characterises light was explained above.Now the origin of light is to be explained. This topic is important tounderstand the functioning of a laser. In this context the particlecharacter of the light is important.

Bohr atom First of all some fundamental principles will be mentioned. As we allknow matter consists of atoms or molecules. They consist of nucleisurrounded by electrons. This is called electron sheath.

Figure 6: Bohr atom

In this atom model developed by the Danish physicist Nils Bohr theelectrons revolve around the atom nuclei like the planets revolve aroundthe sun (Figure 6).

Quantum It was a surprising discovery of modern physics that an atom or moleculecannot emit any amount of energy but only defined "portions". Theseportions are called quantum. According to this model light is not only

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characterised by waves. Depending on the context light can also beimagined as particles. The energy (e.g. by heating) can only be absorbedin defined amounts. More precisely, the energy quantum is absorbed bythe electron sheath.

According to the Bohr atom model (Figure 6), the electrons cannot movealong random paths since the distance between the electron and thenucleus depends on the energy. Only defined distances are "permitted".

These distances are only part of the model. In general we speak of energylevels.

What does the material cause to emit light?

Excitation It must be excited to do so. If for example a suitable amount of energy issupplied to an atom, an electron is "lifted" to a higher energy level. Wesay that it is excited. In Figure 7 the vertical y-axis shows some of theseenergy levels. No special atom is shown, the distances between theenergy levels were selected at random. In principle the figure is similar foreach atom or molecule. There is the lowest stable basic level. The gapsbetween the energy levels become smaller the higher you get. Only anexact amount of energy is important, that is the amount of energy shouldexactly correspond to the distance between two possible energy levels.

Figure 7: excitation

There are different ways of excitation, not only by a light quantum as inFigure 7. If a material, e.g. iron, is heated, it starts to glow. On atom levelthis means that the atoms move faster and faster. They collide with moreand more energy until the energy exactly corresponds to the distance tothe next free energy level. In this case the electron is excited. In thiscontext the term "temperature" is important (see 2.2). The energy canalso be supplied in electrical form, e.g. for an LED, the filament of a lightbulb or in a fluorescent tube.


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Emission This state is not stable. Sooner or later the electron "falls" down to itsbasic level and emits its energy in form of radiation (Figure 8).

Figure 8: radiation

It cannot be foreseen when this will happen, sometimes sooner,sometimes later. This is called spontaneous emission.

What is coherent? When several atoms are excited, they will not all emit radiation at thesame time. The light waves will not have the same rhythm. We say thatthey are incoherent (Figure 9 and Figure 10).

Figure 9: coherent waves

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Figure 10: incoherent waves

What is the direction of the beam? The direction of the beam is not defined either. Normally light is radiatedevenly in all directions or is non-directional.

The radiation, the light quantum, has a defined energy and thus adefined wave length. In the area of the visible light, its colour is alsodefined (see 2.2.3).

2.1.4 Radiation spectrum

What does this light look like? For an LED a defined step between energy levels is preferred. This is whythe light is monochrome. Since the emission of the many electronsinvolved is not simultaneous, the light waves do not have the samerhythm, they are incoherent.

For other materials, such as the metal of a filament, many steps betweendifferent energy levels are possible. This is why the light is notmonochrome here.

In some wave length ranges (in the visible range: colours) radiation ishigher, in others it is lower. A graph with the amount of energy on the y-axis and the wave length on the x-axes shows the spectral distribution orthe spectrum of radiation. To enable a better comparison of the differentemitters, the curves are standardised, the maximum is always defined asthe value 1. Below please find some examples.


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Figure 11: spectrum of solar radiation

4: GaAsP5: GaAlAsP6: GaAs

Figure 12: Spectrum of LEDs

Figure 12 shows that the light of the LEDs is emitted in a very small wavelength range, it is almost monochrome. Curve 4 is in the red range of thevisible light, 5 and 6 are infrared.

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Figure 13: spectrum of the laser diode made of InGaAlP

The spectrum of the laser diode is almost a line at 675 nm. This light iscompletely monochrome. This is explained below (2.3). The laser diodeused in the current units consists of InGaAlP.

For a better overview the spectres were shown separately. The followingFigure 14 shows all spectres.

1: sun light2: sensitivity of the human eye3: spectral sensitivity of the Si receiver4, 5, 6: LED GaAsP, GaAlAsP, GaAs7: laser diode made of InGaAlP

Figure 14: spectral curves

What are the consequences in practice? You can see that the sensitivity of the human eye is perfectly suited forsolar radiation. Curves 3 and 5 confirm the statement of 2.1.2 that thesensitivity of the receiver is well suited for the LED with a wave length of


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880 nm. Another favourable coincidence is that especially in this rangethe solar radiation, curve 1, is less intensive. In the complete infraredrange it is less intensive than in the visible range. Most artificial lightsources such as bulbs or fluorescent tubes have similar characteristics.This confirms that interference by extraneous light can be reduced by theselection of these sensor components.

2.2 Radiation and temperature

In the following paragraph some terms are discussed that are of specialimportance for the understanding of the characteristics of the infraredsensors. The technical data of these units are discussed in 5. Paragraph2.2.3 is important for the understanding of the colour sensor, it does notconcern the infrared sensor.

2.2.1 Black emitters

In general every material emits radiation. The intensity and the wavelength depend on the temperature.Each ideal black emitter has the same curve.

The sun (see Figure 11) is almost a black emitter. For these emitters thecurve is always similar. The position of the maximum depends on thetemperature. For cold objects it is located in the range of the long wavelengths. When the temperature increases, it moves towards increasinglysmall wave lengths (e.g. first steel glows red, then yellow and then blue).

For black emitters it is very easy to determine the temperature. You onlyhave to measure the radiation in a certain wave length range, here in theinfrared range. Strictly speaking, the higher the temperature of the objectto be measured, the smaller the value for the wave length the sensor canreceive.

2.2.2 Emission

However, we deal with real objects and not with ideal black emitters.What does that mean for the measurement?

Measured signal The measured signal is mainly influenced by two factors (see below). Thisleads to the fact that the signal obtained by a simple measurement asdescribed in 2.2.1 has no direct correlation with temperature. Like othertypes of binary sensors the infrared sensor is suited for applications whereit is important that the sensor switches when a certain switchingthreshold is reached. The actual measured value is not known. In thiscase this is not necessary.

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What is the correlation? In this paragraph the correlation between temperature and measuredsignal is described briefly. The two influencing factors are as follows:¡ differences compared to the black emitterNot all materials have a curve along the complete wave length range likethe black emitter. An extreme case is for example an LED. Radiation isemitted within only a small range of wave lengths (see Figure 12). Inmost cases the objects to be detected have almost the samecharacteristics as a black body so that this factor influencing themeasured signal can be neglected.¡ Degree of emissionThe degree of emission (or E) is indicative of the ability of a material toemit infrared radiation. E can assume values between 0 and 1. The higherthe value, the more infrared radiation is emitted. The fact that thischaracteristic of the material can for example be 0.01 or even smaller forcertain objects shows that this is the factor with the highest influence onthe measured signal. In this case the signal would be 100times weaker.Tables containing the value E for different materials can be found in theannex.

On what factors does E depend? If you want to do without tables one simple criterion can be taken intoaccount. The degree of emission depends on the reflection R. Smooth,shining, reflective surfaces have good reflection characteristics. You canimagine that the thermal radiation that comes "from the inside" doesnot go through the surface but is reflected back "to the inside". Suchmaterials have a lower degree of emission.For many materials the correlation is even more complicated because thedegree of emission itself depends on the temperature.

Are IR sensors measuring units? For the measurement of an analogue signal the problem arises that thedegree of emission depending on the material and on the temperaturemust be sensed. Although this is possible from the technical point ofview, this would mean very complex mechanics and electronic evaluation.Quotient pyrometers, as such measuring units are called, are veryexpensive and they can cost as much as a mid-range car or even more.For a long time these units have been supplied by companies such asHeimann, Impac or Ultracust. For these reasons infrared sensors withbinary outputs are offered. These units are less cost-intensive, can beconnected to any controller without any problems and are sufficient forthe majority of applications. The answer is that they are no measuringunits (like most binary sensors).

2.2.3 Reflection and colour

Colour As shown above (see Figure 3) the eye sees different wave lengths asdifferent colours. This is not only the case for objects that emit radiationthemselves but for every object we see. We can only see it if it isilluminated. This means that the light of a light source (sun, lamp) strikesthe object and is reflected. This correlation, that is known as reflectionlaw (angle of incidence = angle of reflection) only concerns idealreflectors. In this paragraph however the diffuse (non-directional)reflection is concerned.


23

Colour filter Most materials have an effect similar to a colour filter. If light strikes forexample sensors of a well-known manufacturer, most wave lengths areabsorbed. Only wave lengths in the orange range are reflected. We saythat the object is orange.

Colour sensor Since a diffuse reflection sensor (see 3.4) reacts to the light reflected bythe object, the term "colour" is discussed briefly in this paragraph.

Black-and-white Let us start with these special cases. Are black and white colours?Spectroscopic tests show that the impression "white" always arises whenthe wave lengths (colours) are evenly emitted in the visible range. We canalso say that white is a mixture of all colours. Accordingly black is theabsence of all colours. If you look at a black-and-white diagram(monochrome, this term is used with a special meaning here) withdifferent shades of grey, the difference between black, white and greycan also be considered to be a difference in intensity.

Contrast Great differences in intensity, no or hardly any shades of grey, are alsocalled strong contrasts. A contrast sensor is thus made for the detectionof differences in intensity.

Science of the colours The impression of colour arises when individual wave lengths arepreferred. The relation is not quite forward as it seems to be, see Figure3. The impression of colour does not arise in the eye alone but by a verycomplex signal processing in the brain. In the arts it has been known forlong, long before the wave lengths were investigated, that three so-called basic colours are sufficient to create any other colour. Intechnology this principle is used to represent for example colours on amonitor or to make a coloured print-out.

Red, yellow, blue These colours are the basic colours. All the other colours result frommixtures of these colours:red + yellow orangeyellow + blue greenred + blue violet.The mixture of all colours is grey ("dark white"). Orange is thecomplementary colour of blue. A mixture of these two colours is alsogrey. This can also be shown by a "chromatic circle" which cannot bedescribed in more detail here (colours are difficult to explain by means ofa monochrome printout, moreover this is an extensive topic which canfill whole books).

RGB In technical applications, e. g. for colour screens or printers the coloursred, geen and blue are chosen as basic colours. In this case we canimagine the colour circle as distorted.

Image processing Shades of colour can be created by different ratios of mixture. Thenumber of possible shades depends on the resolution, here also calleddepth of colour. With one bit for red for example it is only possible toindicate "present" or "not present". With two bits four intensities can bedistinguished etc. Modern software for image processing provides amongothers the function to change the ratio of mixture in fine steps. Thisallows for example to reduce colour casts or to create interesting coloureffects.

red

orange

yellow

violet

blue

green

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In principle three colours are enough, instead of the example of red,yellow, blue the colours orange, green, violet could have been taken asbasic colours. There are high-quality printers with 6 colours. A betterprinting quality is reached because the ratio of mixture cannot bereproduced with the required precision if only three colours are used. For6 colours this error is smaller than for three colours.

What does that mean for the diffuse reflection sensor?If we take for example red objects and illuminate them with a GaAsP LED(see Figure 14), that is with red light, the reflection characteristics are verygood. If you use the same LED to illuminate a blue or yellow object, thereflection characteristics are considerably reduced.The first consequence is that the range depends on the colour.

If you do not consider the kind of surface (rough or smooth) and assumethat it is the same for all objects, you can see that it is possible todistinguish between a red and a blue object. It is however hardly possibleto distinguish between a blue object and a yellow or a grey object withthis sensor.

Colour sensor If objects with different colours or imprints on paper with differentcolours are to be distinguished, a three-coloured light source is required,e.g. in red, yellow, blue. Either a receiver which can measure the intensityof each colour is required or, if the signals in red, yellow, blue are nottransmitted simultaneously but one after the other, a receiver with thesame sensitivity with regard to the three colours. If the receiver only givessignals in case of red, the object must be red. The colour of anotherobject can for example be a mixture of 20 % red, 30 % yellow and 50 %blue. If this ratio is stored, the sensor can distinguish this colour frommany other colours.

If for example a sheet of paper is to be cut at a certain coloured mark(and not at any other imprint!), the Teach function allows to store thiscolour in the sensor.

2.3 Laser

2.3.1 Meaning

What is a laser? This term is an abbreviation and means Light amplification by stimulatedemission of radiation. OK?

Actually laser means a special effect. In the meantime we simply say laserwhen a laser transmitter is meant.

What does a laser transmit? First of all the answer seems to be simple: it is nothing but light. But tounderstand the special features of a laser, what is for example thedifference between a laser and a lamp or LED, you must remember someof the basic principles described above.

In general the emitted light has the following characteristics:¡ non-directional¡ not monochrome


25

¡ incoherent

And this is different for the laser? Correct! To understand the special features of the laser, it is important tounderstand what "normal" radiation is first.

2.3.2 Features

Snowball effect First of all it should be described what stimulated radiation is. You canimagine two atoms. One electron of each atom was lifted to the sameenergy level. Some time one electron falls down and emits its energy.When the light wave passes the other atom, it can be stimulated to emitits energy as well. For the second atom the emission is no longercoincidental. Due to this stimulation the light of the second atom has thesame direction, the same wave length (obvious because of the sameenergy level) and the same rhythm. If not only two but many atoms areinvolved, a sort of snowball effect results.

Why has laser light always the same direction?The question is justified. The first wave that starts the avalanche can haveany direction. It has not been mentioned so far that a laser requiresreflectors. A reflector of the best possible quality is located at one end, apartly transparent reflector at the other end where the light is emitted. Awave that does not strike the reflector at an angle of almost 90° has nochance to cause a big avalanche. It strikes the lateral wall and is absorbed(1 in Figure 15). Only a wave that strikes the reflector vertically isreflected and can be reflected many times between the reflectors. Thisstructure is also called resonator. Only then can the avalanche grow untila "real" laser beam results (2 in Figure 15). Since the number of atomseven in a relatively small diode is incredibly high, you need not wait longuntil this happens coincidentally. The radiation starts almost immediately.

ï

î

Figure 15: principle of a laser

Laser light is:¡ directional (parallel)¡ monochrome¡ coherent

Laser diode In the meantime many lasers (or better laser transmitters) are available.Different materials and different methods of stimulation are used. Itwould be taking things too far to list all of them. Some of them arebriefly mentioned in this text. The type which is most frequently used isthe laser diode. The excitation of the electrons is caused by electricalcurrent. It is true that the laser diode is still the most expensive

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component in laser sensors but the high quantities justify the use of laserdiodes for standard applications (laser pointer). They have no partlytransparent reflector (see above). This task is simply assumed by thesmooth (reflective) surface of fracture of the crystal. This is why the lightis not so exactly parallel as with precision lasers. The still relatively low"dispersion" is however sufficient for use in sensors.

Granular The light spot generated by a laser beam that strikes a wall has acharacteristic appearance. It looks granular which makes it easy toidentify a light source as a laser. This effect can be explained as follows:as described above, laser light is coherent (see Figure 9). The waves thatare reflected by the wall are no longer coherent. Small uneven patchescan already lead to the phenomenon that the light beams that arereflected by the wall and fall into the eye, do not all take the same path.This leads to interference (see 2.1.1). If the crest of a wave meets thehollow of a wave, the light intensity is 0: the spot is dark. Otherwise thelight is intensified: the spot is bright. This effect is also used in practice totest the quality of surfaces of components for optical precisioninstruments. Uneven patches which are smaller than the wave length ofthe laser light, here 875 nm, can be detected in this way.

Energy Since laser radiation in general is almost parallel, it is for example easy tofocus it by means of a focussing lens. Since the complete energy isfocussed, the laser light can be of high energy. It is for example also usedfor cutting or welding. For a photocell this is of course not desirable.Radiation with relatively low energy must be used here. Depending onthe possible effect of the laser light it is divided into different classes. Theuse of laser photocells should for example not oblige persons in this areato wear safety glasses.

How dangerous are laser sensors? Laser sensors should correspond to the European standard EN 60825 orthe international standard IEC 60825. In these standards the operation oflaser systems is covered.

Eyelid closing reflex Laser sensors of ifm electronic are classified in laser protection class II.This is for example also the class of the laser pointer. The laser power,even in the setting mode, is max. 1mW. In this class it is assumed that theeyelid closing reflex is sufficient to protect the eye. If bright light strikesthe eye, the eyelid closes automatically, in a reflex. The eye is exposed tothe light only for a short time. When a laser beam strikes the human eyethe eyelid is closed involuntarily. The laser beam must not cause any harmwhen it strikes the unprotected eye for 0.25 seconds.

When the laser systems are installed, it must be considered, e.g. bycorrect height of installation, that intentional or accidental looking intothe laser beam is prevented. At the place of installation clear warninglabels (included) are to be applied. Additional protective measures anddetailed personnel instructions are not necessary.The use of the units at the height of the head or radiation in directionswhere persons can stay should be avoided.

Except for special high-power lasers, laser radiation is not of high energy.The advantages of the laser light however result in a lower efficiency.Laser light is only dangerous because of the extreme focussing. In thiscontext we should remember that the human eye also has a kind of lens.


27

2.3.3 Terms

Some terms that are often mentioned with regard to lasers will beexplained briefly in this chapter.

Where is the pump? Such a term is "pumping". The meaning of the term is as follows. If thelaser material, gases or solids, is excited e.g. by heating to emit radiation,efficiency would be low because of the different energy levels involved.This is why the material is for example exposed to light, preferably of adefined wave length, for a better excitation of the desired energy level(there are other methods that will not be described here). One exampleof the technical implementation is described briefly here. Everyone thattakes photos knows the modern electronic flashes. The lamp inside, atube filled with a special gas mixture that starts to light by means ofelectrical discharge, is cylindrical. If you imagine such a flashing tube likea coil wound around a ruby crystal, you know what a ruby laser lookslike.

Population inversion With regard to lasers this term has the following meaning. Chapter 2.1.3described that light is emitted when an electron of a higher energy levelfalls to a lower level. This can also be inverted. Light that strikes anelectron on a lower energy level can lift it to a higher level. The better theenergy of the light corresponds to the "gap" between the energy levels,the more probable is this case. In a material that consists of many atomsof the same kind with the same energy level, the light that is emitted byan atom can easily be absorbed by another atom. The above-mentionedsnowball effect requires more atoms with the electron on the higher levelthan atoms with the electron on the lower level. This state is calledpopulation inversion. The term "pumping" can also be used. We can saythat "pumping" is necessary until population inversion has been reached.

Polarisation When the characteristics of the "normal" light were listed (2.3.1) thefollowing feature could have been added:¡ non polarised.

For many laser light sources the light itself is already polarised because ofits structure. Since this is not the case for all types, it should bementioned here.

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2.3.4 Laser sensors

Precision For the reasons given in 2.3.2 laser units are especially suited forapplications that require high precision. We cannot imagine e.g. geodesywithout laser units. For the use of binary sensors this high precision canhowever be disadvantageous if such high precision is not necessary.Practical tips especially for retro-reflective sensors can be found in3.3.2.2. Some points that are important for all types will be mentionedbelow.

Focussing It was mentioned above that depending on the quality of the resonator,the beam is more or less parallel. If in this context high precision isrequired, it is quite difficult to control and correct it if necessary. Forbinary sensors a weak focussing is sufficient. Figure 16 shows an exampleof a typical beam.

Figure 16: beam of a laser unit

It is obvious that the minimum diameter of the light spot is reached at adefined distance (TW). This distance is given in the data sheet of therespective unit. This distance is determined by the selection of the opticalelements. It would be too complicated to make this distance variable. Letus take an analogue example out of the field of photography. A high-quality zoom lens is much more complicated and expensive than a lenswith fixed focus.

Small objects The cheapest solution for the detection of small objects (minimumdiameter 0.1 mm) is to equip the unit with a diaphragm. You only haveto accept a reduction in the range. The detection of tiny objects fromgreat distances is however a rare special case.


29

2.4 RefractionWhy do I have to know this? This phenomenon is important for the understanding of the operating

principle of fibre optics (see 3.5).

Figure 17: refraction transparent -> more opaque

Rays of light which pass from a transparent medium into another moreopaque medium are refracted, i.e. the ray is no longer straight. Althoughrefraction also depends on the angle of incidence the rays are alwaysrefracted towards the perpendicular of incidence, that is the lineperpendicular to the boundary surface of the media at the point ofcontact. It should be considered that there is a critical angle in the glass.Even if the light strikes the glass at a very flat angle (glancing incidence),there is one area in the glass where the light cannot go (see Figure 17).

Why? You could also ask: what does more opaque or more transparent mean?

Velocity of light This depends on the different velocities of light. Perhaps you rememberto have learnt that the velocity of light is an absolute limit value and isalways constant. In this case however another context is referred to thatis important in the theory of relativi ty. (Don't worry, we will not deal withthis theory here). In reality the light velocity depends on the medium. Thehighest value is reached in vacuum, in air it is only insignificantly lower. Inwater or in glass it is considerably reduced with significant differences fordifferent types of glass. An opaque medium is a medium where light isslower. Correspondingly light is faster in a more transparent medium. (Asmall digression might be interesting for some people: now we canunderstand that there is movement with hyperdrive speed and not only in"Star Trek". High-energy particles of radioactive radiation can move withhyperdrive speed in water. It is true that the velocity is always below thelight velocity in a vacuum but it can be above the light velocity in water.This leads to a phenomenon that is similar to the supersonic bang ofplanes. The so-called Czerenkow radiation results. It can be seen as bluishlight that can be seen when a photo of a reactor core in water is taken).

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Refraction index The material characteristic "refraction index" is the ratio of light velocityin vacuum and light velocity in the medium. It is always higher than 1.

Shortest time One might ask why the light path is no longer straight in this case? It isan interesting law of nature that light moves in a way that it goes frompoint A to point B at the shortest possible time. This law explains why theray is no longer straight if point A is in the more transparent medium andpoint B in the more opaque medium.

Inversion What happens if the light passes from the opaque into the moretransparent medium?

Figure 18: refraction opaque -> more transparent

In general an inversion of the light path is always possible. This meansthat if you draw a ray of light from a transmitter to a receiver, thedrawing must also be correct if transmitter and receiver are interchangedso that the direction of light is inverted. This is also the case forrefraction.

Critical angle This works similarly the other way round: when passing from the opaqueinto the more transparent medium, the rays are refracted from theperpendicular. But once a critical angle has been achieved (Brewsterangle), which is already shown in Figure 17, there is no ray of light in themore transparent medium. This angle depends on the two media and isabout 42 degrees for glass-air. The light can no longer be refracted intothe more transparent medium but is totally reflected into the moreopaque medium at the boundary surface according to the law ofreflection (angle of incidence = angle of reflection) instead.

Total reflection Total reflection has more to do with the refraction of light rays than withthe reflection of light. It is more efficient than the best reflector. Itfunctions almost without any losses.

Fibres If a light beam in a glass fibre strikes the wall at a flat angle, it is totallyreflected. By additional total reflections at the wall it is passed oncontinuously and leaves the fibre at the same angle as the one it had at


31

the start. This is also the case if the fibre is bent. The bending musthowever not be too strong, among others because the fibre may break(see 3.5).

1 Light2 Core glass3 Sheathing

Figure 19: Total reflection in fibre

Attenuation The total reflection is almost without any losses. In general the light ishowever slightly attenuated. Even if glass with excellent characteristics isused, you can imagine that light is attenuated when is passes glass panesof a thickness of several meters. Fibres of glass and of plastic are used(see 3.5). An example: in plastic fibres the attenuation is 120 dB/km (theunit dB cannot be explained here, briefly: it is a logarithmic scale, 6 dBmeans attenuation to 50 %). Since the attenuation is higher for infraredrays, red light is used for some sensors.

Structure of a fibre Strictly speaking the total reflection does not take place at the wall of thefibre but already inside the fibre. Special glass fibres consisting of twotypes of glass are used. The inside of the fibre is made of a rather opaqueglass, the outside of the fibre of a more transparent glass. The totalreflection takes place in-between in the boundary area.

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3 Characteristics of photoelectric sensors

At the beginning of this chapter the photoelectric principle of thedetection of objects is compared with other principles. Then the threeindividual sensor systems as well their special features with additionalinformation on applications etc. are described.

3.1 Comparison with other types of sensors

3.1.1 Definition

What does photoelectric actually mean?It means non-contact detection of an object by means of light andelectronic evaluation and transfer of this information.

Sensor systems Photoelectric systems are important components of modern automation.In the future they will probably become even more important. Differentsystems exist:

¡ image-creating (2-dimensional)

As the name says it, images of objects are created, e.g. by a video ordigital camera. These images are processed or evaluated, e.g. with regardto existence, type, position, dimensions of the object etc. Especially thesesystems are more and more often used for evaluation in view of theimproved computing capacities.

¡ length measurement (1-dimensional)

For a long time different types of photoelectric systems have been usedfor length measurement, partly with very high accuracy. In some casesthey are however replaced by image-creating systems. In the broadersense encoders also belong to this group.

¡ photoelectric sensors (0-dimenstional (point))

These sensors are binary sensors. The latest diffuse reflection sensors withbackground suppression become more and more similar to measuringsystems.

Binary sensors The following text only concerns binary sensors. As for all the other typesof binary sensors the information "object (or state) present" or "...notpresent" is sufficient in many applications. A binary sensor then is lessexpensive and more resistant to interference.

Moreover it should be mentioned that the "simple" binary sensors (thisdoes not only concern the photoelectric sensors) are also a low-costsolution for demanding applications. Two laser photocells enable forexample a relatively precise length monitoring. In some applications amatrix of photocells is less expensive than an image-creating system. Thecreativity of the user and the adviser is required here.


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3.1.2 Immunity to interference of different sensor types

Sensor Tempe-rature

Moisture Dust Lightinfrared

Noise el.-magn.fields (HF)

inductive + + + + + ocapacitive + o o + + -photoelectric(diffuse)

o - o - + +

ultrasonic o + + + - +

+ high o mean - low

Figure 20: Influence of interfering factors on different sensor types

The table shows the advantages and disadvantages of the sensingprinciples listed. This is why the units are better suited for one or anotherapplication.

The obvious advantages of photoelectric sensors are their immunity tohigh-frequency electromagnetic fields and to noise. However, the unitsare more susceptible to moisture, extraneous light or infrared radiation.

The table (Figure 20) can also be used to select a suitable sensor for anapplication. In individual cases it must however be checked whethersensor-specific characteristics are to be considered. Temperatureproblems of photoelectric sensors can for example be solved by the useof fibre optics or it must be taken into account that ultrasonic sensors aresusceptible to interfering reflections.

3.1.3 Ranges of sensor systems

The distance at which the object is to be detected is a clear criterion forthe selection of the type of sensor.

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Figure 21: ranges of different systems

Ranges This diagram shows an additional advantage of photoelectric sensingsystems compared to the inductive and capacitive units, the enormoususeful sensing range.

Operational reliability It is the intention to eliminate all possible sources of interference, such asmoisture and extraneous light, and this is why photoelectric sensors, thephotoelectric sensor, called here "efector 200", represents a very goodsystem for the safe detection of objects.

Size An additional great advantage is that the units are really tiny in relationto their sensing range. The OJ unit, for example, is capable of detectingobjects up to a distance of 600 mm, OJB even up to 1000 mm. Especiallythe units with laser diode have enormous ranges and small housings (e.g.60 m as through-beam sensor for type OG). There are no comparableunits in the area of inductive and capacitive proximity switches,particularly with regard to interference immunity.

3.2 Through-beam sensors

3.2.1 Operating principle

How can we imagine the optical detection of objects by means of IR radiation?A through-beam sensor consists of transmitter and receiver mountedopposite each other. Each time an object interrupts the direct pathbetween transmitter and receiver the electrical response of the receivertransistor or the receiver diode changes. This change can be used todetect the presence of an object by means of the electronics and can besignalled via an output stage.In the IEC 60947-5-2 this is called type T.


35

Figure 22: through-beam sensor principle

This principle of the through-beam sensor is one method of detectingobjects which is used for the units.

Transmitter (S) and receiver (E) The two components are briefly designated with S for transmitter and Efor receiver (also in the type key).

T TransmitterR ReceiverSF Sensing area = active zoneWF Useful area = receiver characteristics

Angle of aperture (receiver or transmitter)

Figure 23: transmitter/receiver characteristics

Angle of aperture Figure 23 shows the transmitter/receiver characteristics of the through-beam sensor. Transmitter and receiver form a transmitter or receiver pathwhich is determined by the angle of aperture of the lens (between ±

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0.04° and ± 5° depending on the design). Laser units have the smallestangle of aperture. There is no clear limit between the area illuminated bythe transmitter and the dark area. The highest intensity can be found inthe centre. The greater the angle, the lower the intensity. The angle ofaperture defines the limits of the area where the receiver can be placed(see Figure 24). It should also be taken into account that the value can beslightly different for individual units.

Trend Older units have a larger angle of aperture. The advantage is that theadjustment is easier. The disadvantages are a shorter range and lowerimmunity to mutual interference (see Figure 26). The trend goes towardssmaller angles of aperture.

Light spot The size of the light spot that is visible for units with red light alsodepends on the angle of aperture and the distance. The correlation is asfollows:

( 2)ar

tan arcã

r is half the diameter of the light spot and a the distance to thetransmitter. In Figure 24 other terms are used to show that the data ofthe receiver are concerned here. The formula does not have to be learnedby heart � the diameter of the spot at maximum range is indicated in thecatalogue.

Visibility ( 2) also shows that the size of the light spot is proportional to thedistance. In other words, at a longer distance the intensity of theradiation is spread over a larger surface. Depending on the environmentalconditions (illumination) it is more and more difficult to see the light spot.This makes adjustment more difficult in case of long distances betweenthe transmitter and the receiver.

Mounting Transmitter and receiver must be mounted in a way that the receiver is inthe transmitter path and the transmitter in the receiver path (see Figure24). The longest range and the highest excess gain (operational reliability)with respect to dust and soiling are only achieved when transmitter andreceiver are aligned along the optical axis as accurately as possible. Whenthe units are adjusted, it must be considered that component andmanufacturing tolerances can lead to a different mechanical and opticalaxis.

Alignment The possible arrangement of transmitter and receiver can also bedetermined by means of calculations according to Figure 24. In practicethe trial-and-error principle is rather used. With this sensing system it isdifficult to find the correct arrangement in case of long distances.Fortunately this is seldom the case in practice. The main reason for theuse of through-beam sensors is the high excess gain.


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Angle of aperture (receiver or transmitterI Misalignement of the geometrical axis (receiver)RWA Working sensing range

A = S + E Maximal permissible angular misalignementI = RWA x tan EMaximal permissible lateral misalignement

Figure 24: arrangement of transmitter and receiver

arrangement of transmitter and receiver Size and duration The objects to be detected must have at least the size of the active zone

(optical axis) to completely interrupt the beam towards the receiver. Ifobjects which pass the beam with a certain speed are to be detected, itmust be ensured that the beam is interrupted long enough. This timedepends on the on and off delays and on the maximum switchingfrequency of the receiver. The object must thus be increased or thetransport speed reduced correspondingly (see 3.8).

Laser The features of these units are slightly different from the featuresdescribed above. The lens slightly focuses the beam. After passing thelens the beam becomes smaller until the smallest diameter is reached. Itthen becomes slowly wider (see Figure 16). As a consequence threezones can be distinguished:

Close range Directly in front of the lens, in front of the unit, the diameter of the lensis important. The object should at least have this diameter to guaranteesafe detection.

Smallest detectable object The special advantage of laser units is that particularly small objects canbe detected. The focussing enables a better use of this advantage. Theyshould be in the range of the minimum diameter of the light spot.

Far range As for the units described above, the beam becomes wider in this rangeuntil the receiver no longer responds. If the rays were exactly parallel, thelight spot would be clearly visible even at long distances and high rangescould be reached. This is however only achieved with precisioninstruments. In this case an exact alignment of the receiver would bemuch more difficult. Moreover production tolerances would lead to greatdifferences in the range. This is prevented by focussing.

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The values for the smallest detectable object, for the maximum diameterof the light spot etc. depend on the type and are given in the datasheets. An example is given in 2.3.4.

3.2.2 Information on the use of through-beam sensors inpractice

Mutual interference of several through-beam sensors

When two or more of these through-beam sensors are to be mountedside by side, care must be taken that the sensors do not interfere witheach other. So a minimum distance e (in Figure 25 represented by thearrow ) should be reserved and depends on the angle of aperture ofthe beam paths and the transmitter/receiver distance.

Distance e

Figure 25: minimum distance of two through-beam sensors

The correlation is described by the following formulas:

( 3) ø ÷e RWA S Stan 1 2 or

( 4) ø ÷tan S EARW

e1 2õ ã

What should be done? In practice there are situations where it is difficult to avoid such anarrangement. Several options exist to prevent interference.

When several through-beam sensors are mounted in parallel, thealternate mounting of transmitter and receiver is good aid (see Figure 27,here the distance e could be 0 in the extreme case).


39

Figure 26: mutual interference of through-beam sensors

Figure 27: alternate mounting of transmitter and receiver

Also, caps or screens between the beam sensor pairs avoid interference.When using caps note that too long a cap reduces the range (excessgain)(see Figure 32).

Reflective objects Reflective objects can also lead to mutual interference of through-beamsensors.

Figure 28: interference of through-beam sensors by reflective objects

What can be done? Screens can for example be used here.

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Figure 29: screens for through-beam sensor 1

Interference by extraneous light To exclude interference which may be caused by extraneous light duringmounting already, the units should be mounted in a way that extraneouslight is prevented from directly striking the receiver lens.

Figure 30: interference by extraneous light

What can be done? This can for example be prevented by transversely arranging the opticalaxis towards the extraneous light source or by placing a cap with a non-reflective lining onto the receiver.

Figure 31: changing the transmitter/receiver lens


41

Figure 32: cap on receiver

Another less adequate solution is to reduce the receiver sensitivity. Butthis also reduces the sensing range of the system and thus the excessgain.

Reflections in the environment Other problems may arise from a reflective surface.

Figure 33: reflective surface

What can be done? Possible solutions are:¡ place transmitter and receiver onto spacers to increase their distance

from the surface;¡ reflection from the surface can be eliminated by means of a non-

reflective covering;¡ reflection can be diverted or absorbed by means of screens mounted

on the surface.

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Figure 34: spacers

Figure 35: screens for through-beam sensor 2

Characteristics of the through-beam sensorsThe following overview summarises the main characteristics.

¡ long range because the light covers only one direct way from thetransmitter to the receiver.

¡ high excess gain¡ large working range, from the "start to the end" of the optical axis¡ precise switch point along the optical axis¡ 2 separate units must be mounted and connected¡ unsafe detection of transparent objects¡ safe detection of opaque objects¡ accurate adjustment is absolutely required for safe operation

Transparent objects can sometimes be detected if the sensitivity of thereceiver is changed. To achieve the highest possible excess gain, thesensitivity of the receiver should however always be set to maximum.


43

3.3 The retro-reflective sensor


Another method for an optical detection of objects is the so-called retro-reflective sensor. The principle is similar to the through-beam sensor buttransmitter and receiver are incorporated into one single housing. Thetransmitted beam is reflected by means of a reflector so that it strikes thereceiver. This principle is also based on the interruption of the light beamto the receiver being evaluated (called type R in IEC 60947-5-2).

Figure 36: retro-reflective sensor principle

Flat reflector If the reflector is not exactly perpendicular to the optical axis, thereflected light no longer strikes the receiver. But even with aperpendicular alignment only a little light is reflected towards the receiversince if a normal mirror is used, the light beams are reflected in the angleof incidence away from the perpendicular. That means that only thebeams which strike the mirror vertically are reflected to the receiver. (seeFigure 37).

Prismatic reflector In order to avoid this, that is in order to attain that as much light aspossible reaches the receiver, a prismatic reflector is used. Unlike thenormal flat reflector the light beam is always reflected back to theperpendicular at the angle at which it struck the reflector.

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Figure 37: reflector for retro-reflective sensor

15° Simple mounting is possible since the prismatic reflector can be installedup to 15 degrees transversely to the transmitted beam without bigreflection losses.

A prismatic reflector consists of many small prisms, i.e. triples, which youcan imagine as the cut-off edges of a cube (rectangular prisms). It can beproven that the reflection of each ray of light that strikes the triple prismat an angle that is not too inclined (o 15° is a considerable margin) isexactly parallel towards the direction where it came from.

Figure 38: reflection at a triple prism

This is difficult to show in a three-dimensional drawing, this is why Figure38 is a two-dimensional drawing. You can see that the reflection of a raythat strikes the surface at an angle of exactly 45° is exactly parallel (evenif it is slightly shifted). If you consider the law of reflection (angle ofincidence = angle of reflection) you can see that even the sharp-angledray is reflected in parallel.

What is a prismatic reflector like? Figure 39 shows one. In some cases theplastic itself has good reflective characteristics so that it need not beprocessed further. In most cases good reflective quality is achieved by athin aluminium coating (aluminisation). The characteristics which are ofimportance for practical use are described in 3.3.2.2 and 3.3.2.3.


45

You can also see that it is difficult to show the reflection in threedimensions. To understand the functioning of a prismatic reflector, thetwo-dimensional drawing of Figure 38 is sufficient.

Figure 39: structure of a prismatic reflector

Prismatic reflectors and laser units Here the special characteristics of the laser have to be taken intoconsideration. This subject is discussed in a separate chapter, chapter3.3.2.2.

Reflective foil Instead of a prismatic reflector a reflective foil can also be used. Whensuch a foil is used, the light is also reflected back into the incidentdirection. But the sensing range of the retro-reflective sensor is reducedto about 70 %.

1 Transparent layer2 Glass balls3 Base carrier4 Reflective layer

Figure 40: structure of the reflective foil

For a reflective foil glass beads are applied on a reflective layer and fixedwith a transparent layer. A basic layer used as carrier is below (Figure 40).The light beam is shown in Figure 41.

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T Transmitter (light source)R Receiver (photocell)

Figure 41: light beam when a reflective foil is used

Nowadays reflective foils with better reflective quality are available. Forthese foils triples are used instead of glass beads.

The characteristics of the prismatic reflector are given in Figure 42 below.

1 Reflection from prismatic reflector2 Reflection from white paper

Angle of incidence

Figure 42: reflective quality of the prismatic reflector depending on the angle

Figure 42 shows the good reflective quality of the prismatic reflector fordifferent angles of incidence. This is a so-called "typical" curve.

Typical As in other graphs typical graphs are shown here. This means that thegraph is different for different units, here prismatic reflectors. This graphclearly shows the characteristics. It would be much too complicated tomake such a graph for each prismatic reflector and each retro-reflectivesensor. In practice it is not important whether the maximum of a high-quality reflector is 75 % or whether the graph is a bit wider for anotherphotocell.


47

As in Figure 23 for the through-beam sensor the following Figure 43shows the characteristics of the retro-reflective sensor.

1 Prismatic reflektorSF Sensing area = active zoneWF Useful area = receiver characteristics

Angle of aperture

Figure 43: receiver characteristics of a retro-reflective sensor

The size of the active zone of retro-reflective sensors changes along theoptical axis. At the unit it almost corresponds to the diameter of thereceiver lens, increases towards the prismatic reflector until it equals thesize of the diameter of the reflector. If an object is to be sensed there, itmust at least cover the complete diameter of the reflector. The object canbe smaller when it is located nearer to the receiver. In order to guaranteea safe detection of the object, its minimum size thus depends on the sizeof the reflector and on its distance to the receiver. It should be noted thatthe range of the retro-reflective sensor depends on the size of theprismatic reflector. In data sheets and in the catalogue the maximumvalue for TS80 (prismatic reflector with a diameter of 80 mm) is given.

Adjustment aid The following method enables an exact adjustment of the reflector: Thereflection space of the reflector is decreased with adhesive tape so thatonly the centre remains free. If the sensor operates correctly, it is exactlyaligned to the centre of the reflector. When the adhesive tape isremoved, the optimum operational reliability has been achieved.

The following characteristics of the retro-reflective sensor can be listed:

¡ Sometimes transparent objects can only be detected if the sensitivity ofthe receiver is changed.

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Please note that the sensitivity of the receiver of through-beamsensors or retro-reflective sensors should always be set tomaximum in order to guarantee maximum operational reliability.

¡ Reflective objects may not be sensed.

3.3.2 Use of retro-reflective sensors in practice

3.3.2.1 Sensors with polarisation filter

How can reflective objects be detected?

There are two possibilities

1. Direction of light By transversely arranging the axis retro-reflective sensor/reflector to theobject, the light can no longer be reflected from the object to thereceiver. A safe detection of reflective objects is thus possible.

Figure 44: reflective objects 1

Figure 45: reflective objects 2

2. Retro-reflective sensor with polarisation filterThe retro-reflective sensors with polarisation filter ensure safe detectionof reflective objects. The light emitted by the transmitter of such a retro-reflective sensor has wave patterns of random orientation (see 2.1.1).This is the case for almost every light source (exception: certain lasertypes). The restriction of these wave orientations towards a preferencedirection is called polarisation. This is achieved by polarisation filters.

A polarisation filter (polariser) ensures that the light is polarised in aspecific direction before leaving the unit, i.e. only light of a specificorientation is emitted. If this light strikes a reflective object (e.g. metal


49

tins, glasses, mirrors), the direction of polarisation of the reflected lightdoes not change. This light is reflected in the direction of the receiver. Asecond polarisation filter (analyser) is incorporated into the housing infront of the receiver with a filter which is aligned vertically to the firstfilter. This means that the beam cannot reach the receiver (see Figure 46).The unit evaluates the interruption of the beam and signals the detectionof an object.

Figure 46: reflection at the object

But if the beam strikes a prismatic reflector, the spreading direction ofthe transmitted light is rotated by about 90 degrees. Such modified lightpasses through the second polarisation filter on its way back to thereceiver. This means that "no object sensed" is evaluated.

Figure 47: reflection at the prismatic reflector

The simple standard reflective foil does not turn the direction ofpolarisation! Thus it cannot be used for a sensor with polarisation filter.

As an accessory a reflective foil especially designed for use with retro-reflective sensors with polarisation filter is available. It has the samecharacteristics as the prismatic reflector, i.e. to turn the direction of

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polarisation. In order to achieve the highest range or excess gain, the foilmust always be aligned vertically to the lens, that is in accordance withthe alignment of the polarisation filter.

Most of the units with polarisation filter are equipped with a red lightdiode since the polarisation filters used guarantee good functioning onlyin the range of visible radiation.

Notes:¡ By means of the filters and the red light transmitting diodes the

sensing range of the sensors is reduced to about 50 % compared tothe "normal" sensor of this type.

¡ It must be considered that multi-layer highly reflective foils withmetallic lining, e.g. food packagings, or metallised cardboard boxeswrapped with transparent foil, e.g. as used for wrapping gifts orsweets, can have the same effects as the prismatic reflector. This canalso be the case if a foil is tightened during packing. That means thatif such objects are sensed by means of the retro-reflective sensor, thepolarisation direction of the transmitted light is rotated so that theobject in the foil may not be detected.

Reliability Interference by reflections at the object must be expected in manyapplications. In practice sensors with polarisation filter are used in mostcases to exclude this interference from the start. The reduction of thesensing range is easier to accept because the maximum sensing range isrequired only in some special applications (also see 3.2.2 and 3.7).

3.3.2.2 Laser units and prismatic reflectors

Lasers and prismatic reflectors Retro-reflective laser sensors are a current topic. Their principles aredescribed in 2.3. In practice it has become obvious that the quality of theprismatic reflector is of special importance here.

The focussing of the laser beam is very precise. Depending on the type(see 2.3.4) the diameter of the light spot is so small that reliablefunctioning of the sensor can no longer be guaranteed if the beamexactly strikes the edge of a triple prism. This can be shown by means ofa simple prismatic reflector that is located not too far away from thephotocell. If the reflector is moved to and fro in front of the laser sensor,the output chatters. Every time the light beam strikes an edge, notenough light is reflected. The sensor evaluates this as an interruption ofthe light beam by an object.

This is the reason why special high-quality prismatic reflectors for retro-reflective laser sensors were added to the range of accessories.Depending on the distance different types should be used. If the reflectoris mounted at the distance where the laser beam has its smallestdiameter (for the data please see 2.3.4), a prismatic reflector with verysmall triple prisms should be used. This guarantees that the beam cannotonly strike an edge. It should also be considered that the higher thenumber of triple prisms, the higher the percentage of edges with regardto the complete surface. As a consequence the sensing range is reducedfor these reflectors. They should thus only be used in the describedcritical range and not for long distances.


51

Overview ranges In the annex on page 160 you will find a table with range values for thedifferent types of sensors on the different reflectors.

Summary Reflector at a small distance special reflector (�laserreflector�)Reflector at a greater distance standard reflector�Small� means the distance at which the beam diameter is small, seeFigure 16. �Greater� means the distance at which the beam has at leastthe diameter of a triple prism.

3.3.2.3 Prismatic reflector

The following statements refer to all retro-reflective sensors, not only tolaser units. The ranges are indicated in the table on page 166.

When the importance of the quality of prismatic reflectors for laser unitsbecame obvious, a new supplier for these accessories was selected. Thenew generation of high-quality prismatic reflectors is used for all retro-reflective sensors.

Sensing range There are different manufacturers of prismatic reflectors thatmanufacture these reflectors for different purposes. In principle a retro-reflective sensor functions with any prismatic reflector (restriction: sensorswith polarisation filter, see 3.3.2.1). In this context it should beconsidered that the data for the range refer to certain reflectors. If otherreflectors are used, the sensing range changes. Since high-qualityreflectors are used as a reference, a reduction in the sensing range mustbe expected when other reflectors are used. The structure of theprismatic reflector (size of the triple, material etc.) has also influence onthe other characteristics (see 3.3.2.2 and below).

Prismatic reflector at close range The quality of a prismatic reflector depends on the precision duringmanufacture. A slightly inaccurate angle, especially at short distances, isnot disadvantageous. The photocell can of course not function correctlywhen the light emitted by the transmitter is reflected back to it. In thiscontext bigger triple prisms are better so that the parallel displacement isas large as possible (see Figure 38), so that the light can strike thereceiver.

Dead zone If the reflector is mounted too close to the retro-reflective sensor itcannot function in a satisfactory way. This is called dead zone. Of coursethe retro-reflective sensor also operates according to the principle of lightbeam interruption in the dead zone, however, the prismatic reflectormust not enter the dead zone. The size of the dead zone for the differenttypes is indicated in the table �ranges on prismatic reflectors� on page166.

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Autocollimation The types OCP, OCPG, OCPL, OJP and OJPL are not affected by theproblem posed by the dead zone. These units operate to the so-calledprinciple of autocollimation. Here the transmitters and receivers �see�through a lens. The transmitter and receiver beam are only separated inthe unit by a semipermeable reflector. This beam path is also calledconfocal.

Figure 48: operating principle autocollimation

On the other hand the sensing range (or excess gain see 3.7) is of coursereduced if the reflector leads to a wider beam. Moreover it is complicatedto manufacture precise reflectors with large triple prisms. Such prismaticreflectors are made of glass and are more expensive than plasticreflectors.

Material and temperature The optical area of most prismatic reflectors is made of PMMA (acrylicglass) and the carrier of ABS. The individual prisms of these reflectortypes are temperature sensitive. To maintain the optical properties plasticprismatic reflectors should not be used at temperatures above 58 °C(temperature range of the standard prismatic reflectors -10...58 °C). Inhigh temperature areas glass prismatic reflectors should be used.

Glass reflectors and polarisation filters Attention: Depending on the design glass prismatic reflectors cannotrotate the plane of light and are therefore not suited for use withpolarisation filter units.

Fixing Permanent reliable operation of reflectors is ensured by good mechanicalfixing. There are three possibilities depending on the type of the prismaticreflector:1. screw connection by means of the existing bore holes2. screw connection by means of injected thread3. connection by push-fit fastener

Reflectors with a smooth back without these mechanical fixing supportsare glued using:1. double-sided adhesive tape (e.g. for carpets) or2. a suitable glue or3. silicone (e.g. sanitary silicone or silicone for building purposes).

Acrylic glue should not be used.

For all kinds of gluing clean and fat-free contact surfaces are aprerequisite.

semipermeable reflector

transmitter

receiver


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Counting bottles This application is critical because the light beam is only slightlyattenuated if it penetrates the surface of a transparent object made ofglass or plastic (foil) vertically. Unexpected effects can also result at theedges of the object. A unit with special features, the OCPG, has beenespecially designed for this particular application. If transparent objectsare to be detected, it must respond to small signal changes. As aconsequence it is particularly sensitive to soiling. For this unit this iscompensated by an automatic adaptation of the switching threshold tothe degree of soiling.

3.3.2.4 Summary

Characteristics of the retro-reflective sensors

Below the main characteristics are summarised briefly.

¡ medium sensing range, about half the range of the correspondingthrough-beam sensor because the beam path is twice as long

¡ only one electrical unit for transmitter and receiver¡ simple installation of the prismatic reflector or the reflective foil¡ precise detection of the objects along the complete optical axis (the

correlation between the size and the distance of objects may have tobe considered, see Figure 43)

¡ safe detection of reflective objects for units with polarisation filter¡ unsafe detection of transparent objects¡ safe detection of opaque objects

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3.4 Diffuse reflection sensors


The diffuse reflection sensor is another photoelectric sensor for thedetection of objects. The basic sensing principle corresponds to a retro-reflective sensor. Transmitter and receiver are also incorporated into onesingle unit.

Figure 49: operating principle diffuse reflection sensor

Similar to the retro-reflective sensor the diffuse reflection sensorevaluates the reflected light. The diffuse-type sensor, however, does notwork with the light reflected by a prismatic reflector or a reflective foilbut with the light reflected by the target object. This is the sensingprinciple which comes closest to the operating principles of inductive andcapacitive proximity switches (type D to IEC 60947-5-2).

There are two different states:

object present object not presentreflection of the transmitted lighttransmitted light strikes the receiverobject sensed

no reflection of the transmitted lightno light strikes the receiverno object sensed

The states of the switching output are described in 3.6.

Compared to through-beam and retro-reflective sensors the diffusereflection sensor has the following advantages:

¡ simple installation since only one unit must be mounted¡ no maladjusted or soiled reflector¡ detection of transparent object safer than with the through-beam or

retro-reflective sensor.

However, when diffuse reflection sensors are used the following aspectsshould be considered:

¡ Since the direct reflection of the light by the object is sensed andevaluated, the detection of objects depends to a high degree on the


55

reflective quality, that is the surface characteristics and the colour ofthe object (e.g. smooth, reflective, white, grey, black).

¡ Since the reflective quality of the objects is in general lower than thatof the prismatic reflector for example (see Figure 42), the maximumpossible range for sensing objects is shorter than for through-beam orretro sensors (active zone). There is no defined switch pointindependent of the object since this point also depends on thereflective quality of the object.

1 receiver characteristicT angle of aperture

SF Sensing area = active zoneWF Useful area = receiver characteristics

Figure 50: receiver characteristics of the diffuse reflection sensor

Figure 50 shows the typical receiver characteristics of a diffuse-typesensor. Similar to inductive and capacitive proximity switches the lines onthe diagram result from a reference object (white back of a Kodak GrayCard) being laterally or frontally approached.

The switch-on/switch-off curves are also similar to those of otherproximity switches. The hysteresis can be clearly determined for lateraland frontal approach of an object of particular size to guarantee safeswitching of the opto efector (see Figure 41).

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Figure 51: switch-on curve

3.4.2 Notes on the use of diffuse reflection sensors in practice

3.4.2.1 Range

What does "range" mean in practice? The range given in the data sheets refers to a reference material. Noexact values for materials with other characteristics can be calculated onthis basis. Practical tests are required to find out whether the range issufficient to guarantee safe detection of certain objects. The referencematerial can be replaced by white paper, 200mm * 200 mm which isroughly the same.

It is not always easy to quantify the dependence of the range from thecharacteristics of the object. The following characteristics have influenceon it:

Surface The most obvious fact is that a big object can reflect more light than asmall object so that the range particularly depends on the size of theobjects.

This is illustrated in Figure 52. This is again a "typical" graph (see 3.3.1,explanation concerning Figure 42).


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Figure 52: range and surface

Colour In general light colours have a better reflective quality than dark colours.Paragraph 2.2.3 explained that the colour of an object results from thefact that certain ranges of wave lengths have better reflective qualitythan others. We can of course only see this for visible light. The reflectivequality for infrared light may differ considerably from that of the visiblerange. This means that you cannot always rely on the impression ofcolour. With this restriction the correlation between colour and range canbe shown in the following "typical" graph. In most cases there aredifferences in the ranges for different colours, but these differences aresmall.

Figure 53: range and colour

Exposure A similar problem exists for the exposure meter in photography. It is setto a degree of reflection of 18 % for a grey surface (Kodak Gray Card).Especially for coloured objects this can lead to incorrect measurements.

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Surface characteristics It is not so easy to enter the correlation between the range and thesurface characteristics in a graph. A thumb rule is: smooth surfaces havebetter reflective quality than rough surfaces.

In practice both influences can occur at the same time. It is obvious that apolished metal surface has better reflective quality than black velvet forexample. For a smooth and dark or a light and rough surface however itis not always easy to foresee which effect will be stronger. The easiestway to find this out is to do tests.

Is a longer range more reliable? Since it is difficult to determine the influence of the materialcharacteristics on the range, we could come to the conclusion that thebest solution is to use a diffuse reflection sensor with the highest possiblerange. This is however not the case because the following point also hasto be considered.

Background The diffuse reflection sensor is susceptible to interference by objects withgood reflective quality in the background. This is caused by the fact thateven light surfaces, e.g. white paper, reflect an only relatively smallquantity of light back to the receiver (see Figure 42). A smooth surface,e.g. a window pane or a reflective foil on clothes can interfere with thediffuse reflection sensor even at distances that are many times the range.

Briefly The characteristics described so far are summarised below for a betteroverview:

Most important characteristics of diffuse reflection sensors

¡ The range depends on the colour and surface of the object.¡ The diffuse reflection sensors must be set in a way that they safely

detect the object but not the background.¡ Problems may result from reflective or very light objects even outside

the sensing range.

What shall we do? In general there are two possibilities¡ optimised setting¡ use sensors with special features

3.4.2.2 Setting

First of all it should be mentioned that in general the sensitivity shouldnot be changed. This is also the case for the diffuse reflection sensor andeven more for the through-beam and retro-reflective sensors. If thebackground interferes with a diffuse reflection sensor, a sensor withbackground suppression is the best solution (see 3.4.2.3). The usershould consider that a change in the sensitivity set at the factory mostlymeans a reduction in the range. This leads to a lower excess gain (see3.7).

What does optimum setting mean ? The answer refers to the excess gain and is explained in details in chapter3.7. In most cases optimum setting means that the excess gain referredto the object and the background is the same.


59

Setting in practice There are two types of setting:¡ manual¡ automatic

Manual This type of setting is used for sensors with potentiometer. Proceed asfollows:

1. Place the object within the normal sensing range.2. Increase the sensitivity with the potentiometer until the diffuse-

type sensor senses the object (output switches) and remember theposition.

3. Remove the object and increase the sensitivity until the diffuse-type sensor responds to the background.

4. Turn the potentiometer back until the output is reset.5. Now set the potentiometer, if possible, to a medium position

between positions 2 and 4 and the sensor has its optimum settingfor this application.

Manual setting is an option for type OB which has an electronicpotentiometer for this purpose. It is facilitated by the LEDs indicating theexcess gain (see 3.7).

Automatic For this type of setting the light intensity of the object and of thebackground is measured. The measurement is started by pressing abutton. The sensor itself then selects the optimum setting (see 3.7).

N.B.! For some units the correct sequence has to be considered.

Trend For newly developed types setting is usually automatic. The advantages ofthis method are described below.

Which method is better? It is obvious that the automatic setting should be preferred for severalreasons.¡ optimumThe above-mentioned optimum setting is almost impossible with thepotentiometer. Even if the exact excess gain were known (the resolutionof the display is quite rough for the OB), you would require a pocketcalculator and the formula to determine this value.¡ dynamicIn some cases, e.g. for a readjustment during operation it is not possibleto measure the reflection of a non moving object. The automatic settingis also possible in the dynamic case. This means frequent signal changescaused by an alternate detection of an object and the background, e.g.when objects pass the sensor on a conveyor belt.¡ simpleErrors during setting are almost impossible (exception: when thesequence, first object, then background, has to be adhered to). Notechnician is required for a readjustment of the sensor, not even duringoperation (see point dynamic). In unfavourable circumstances the unitindicates that reliable setting is not possible. You can then look for betteralternatives immediately.¡ tightA potentiometer is a weak point for every housing. If it is damaged,water or oil can get to the circuit. If no suitable screwdriver is available,damage can occur easily. A tight potentiometer is very expensive.

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As a consequence almost all units of the new generation only havebuttons and no potentiometers. Prerequisite is the use of microprocessorsin the unit. In this case buttons enable easier and better setting as well asmore reliable sealing which leads to a better operational reliability.

We have now completed describing the optimum setting.

If setting is not possible? In practice there are cases where setting of the unit is not possible.Typical problems are for example:¡ highly reflective surfaces in the background¡ light objects and light background¡ small distance between object and backgroundAs already mentioned the unit with automatic setting indicatesunsuccessful setting. In this case we must assume that manual setting isnot possible either. The alternative would be to use units with specialfeatures as mentioned above.

Angle One piece of information at the end: if light is reflected by a smoothsurface in the background and interferes with the diffuse reflectionsensor, the reason for this can be that the light strikes this surfacevertically. This could simply be prevented by changing the angle.

3.4.2.3 Background suppression

The different operating principles as well as the technical solutions will beexplained in detail below. The specific features of the units will also bedescribed. Let us start with a short overview. We distinguish:¡ diffuse reflection sensors for short ranges¡ fixed range¡ diffuse reflection sensor with background suppression¡ adjustable range

There are different possibilities to set the range:¡ mechanically¡ The light beam strikes a reflector. By changing the angle of the

reflector mechanically, the distance from which the light beam strikesthe receiver is changed. Despite the mechanical elements this methodis quite exact and reliable and enables the manufacture ofastonishingly compact types. It is used for a number of units and willremain important for the time being.

¡ electronically¡ This concerns the change in sensitivity by means of a potentiometer.

Strictly speaking it is not the range that is reduced but the excess gain(see 3.7). Actually this method does not concern the setting of therange and is only mentioned to complete the picture. Moreover thenew units have no potentiometer but membrane keys forprogramming.

¡ optical background¡ In the end the signal evaluation is always electronic. However, in PSD

technology or with a diode array an optical effect is used. We knowthis effect from photography. In the zone of sharpness a spot isshown as a spot. A spot outside this zone is shown as spot with fuzzyedges. If the receiver element can resolve the shape of the light spot,it can also define the distance. These systems are expected to becomemore important in the future.


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Short-range diffuse reflection sensor and diffuse reflection sensor with background suppression

What is the difference? The operating principle is similar. The short-range diffuse reflectionsensor that is described first is simpler and has fewer features. The diffusereflection sensor with background suppression enables a betteradaptation to different conditions.

Figure 54: diffuse reflection sensor with and without background suppressionin accordance with the focussed beam principle

Dead zone In Figure 54 the dead zone can be clearly seen. An object immediately infront of the diffuse reflection sensor reflects most of the light back to thetransmitter. The plane of section of the light cone of the transmitter andthe (imagined) one of the receiver must be large enough so that enoughlight strikes the receiver.

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In the case of the retro-reflective sensor the dead zone only has to betaken into account for the distance of the reflector (see 3.3.2.3). Theposition of the object or whether it interrupts the transmitted or receivedlight is of no importance. In the case of the diffuse reflection sensor,however, the dead zone is the zone in which the object is not detected.Further on you will find a description on how the dead zone is virtuallyreduced to 0 with the new units.

Figure 54 again shows the operating principle of a diffuse reflectionsensor. A change in the position of transmitter and receiver, as is shownin the lower part b of the figure, leads to some kind of backgroundsuppression. Irrespective of the nature of the background, it will hardlyinterfere with the sensor outside the overlapping area of transmitter andreceiver. This method is called focussed beam principle and is used forthe so-called short-range diffuse-type sensors.

Note that the receivers are set to a defined sensing range at the factory.This range must not be changed since in this case the backgroundsuppression is only determined by the position of the lens. A change inthe sensitivity would only reduce the excess gain. The angle betweentransmitter and receiver beams is achieved by means of an injection-moulded part inserted into the lens.

Sensing range In comparing the technical data of such a short-range diffuse reflectionsensor with a standard diffuse reflection sensor of the same type, asensing range loss of 70 to 80 % is caused by this principle. As anexample of this, the type OUT has a range of 200 mm and the OUNdiffuse reflection sensor for short ranges only 40 mm. But the sensingrange of short-range diffuse reflection sensors is almost independent ofthe colour and surface characteristics of the object (white paper, blackfelt). Also, the unit is less susceptible to interference from thebackground.

Results when diffuse reflection sensors for short ranges are used:¡ sensing range is approx. 20 % of that of the diffuse reflection sensor¡ no interference from a reflector or other highly reflective objects in

the background.

A second principle used for background suppression works with twodifferent receivers.

Figure 55: triangulation principle


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Triangulation principle This triangulation principle evaluates the reflection of the remote lightand the close light by means of two receivers, thus also obtaining abackground suppression. this principle is used for the units OCH, OAHand OTH. The angle between the receivers can be changed by means ofan adjustable mechanism.

1 Semipermeable reflector2 Receiver3 Emitted light4 Object5 Background

Figure 56: setting of the sensing range

Sensing range Figure 55 shows the principle, Figure 56 the technical solution. By meansof the mechanically adjustable reflector the range can be set, e.g.between 20 and 250 mm for OCH. This enables a better adaptation tothe individual applications. The setting is relatively precise. Under idealconditions one sheet of cardboard more or less on a stack can bedetected. The user may not see any difference between the adjustmentof the range by a potentiometer or by a reflector. These cases shouldhowever not be mixed up.

Sensitivity The setting of the sensing range of a standard diffuse reflection sensor(see 3.4.2.2) almost always means a reduction in the sensitivity. Theexcess gain is reduced (see 3.7), which makes the unit more susceptibleto soiling. In addition the dead zone increases. In many cases it is thus abetter solution to use a unit with special features instead of a standarddiffuse-type sensor. For these special units setting of the sensitivity is notprovided. The setting of the range as described here is made in adifferent way. These units are set to maximum sensitivity from the start.As a consequence the switch point is almost independent of the colour ofthe object. This is the best solution for the detection of transparentobjects.

PSD This abbreviation means position sensing device. If you replace the tworeceivers in Figure 55 or Figure 56 by a plain receiver, you get an idea ofthe operating principle of PSD. Instead of a point receiver that providesone binary signal (light received - no light received) the PSD is a planereceiver. It provides an analogue signal that depends on the percentageof light striking the surface. This is a first step from a binary sensor to animage-creating sensor (used e.g. for OGH).

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Diode array In the meantime it has been found out that even better results can beachieved using an array of receiver diodes. It can be deduced from Figure56 that a modification of the object distance causes a change of theangle. The light from the object and the background strikes differentreceivers. A slight shifting of the object near the sensor causes a greaterchange of the angle than that of an object which is located at a greaterdistance. Therefore there are receiver diodes with different widths (forexample used for the type OJ).

Setting If the light reflected by the object and by the background is different, thisdifference can be evaluated electronically and no mechanically adjustablecomponents are required any longer. This method is used for OGH andOLH. As for OGT or OLT for example, they are set by pressing a button.Since the operating principle is however different, the disadvantage ofthe reduced excess gain is prevented.

Extraneous light Since for these methods, triangulation or PSD, a difference is evaluated,these units are less susceptible to interference by extraneous light.

3.4.2.4 SummaryAdvantages of the diode array The new generation of units with background suppression, especially by

means of a diode array, has the following advantages:¡ no mechanics¡ automatic adjustment¡ lower susceptibility to interference by extraneous light¡ virtually no dead zone

Characteristics of the diffuse reflection sensor In general the typical characteristics of the diffuse reflectionsensor can be summarised as follows:¡ direct sensing of objects, so no reflector or second unit is required¡ safe detection of transparent objects¡ short sensing ranges compared to the through-beam and retro-

reflective sensors¡ the sensing range depends on the reflective quality (colour, surface) of

the objects to be detected¡ no precise switch points¡ interference from the background possible (mirror, metal, white)

¡ the diffuse-type sensors for short ranges or with backgroundsuppression are an exception, however their sensing range is reduced.


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3.4.3 Units with special features

A number of units with special features are offered for specialapplications. They will not be discussed as thoroughly as standard units.

Foreground suppression In most cases interference of a diffuse-type sensor is caused by lightobjects in the background. This is why the units with backgroundsuppression are described in details in 3.4.2.3. If for example thebackground has better reflective quality than the objects, the backgroundsuppression may be no solution. In these cases sensors with foregroundsuppression, the OCV, can be used. Their operating principle is similar tothat of a retro-reflective sensor by using the background as a reflector.The interruption of the light beam is evaluated.

Small objects As for the through-beam sensors this is a typical application for laserunits.

Types OG and OL are available as diffuse reflection laser sensors (OGTLand OLTL). Their special feature is however the fixed focussing of thebeam to 50 mm. As a consequence the smallest detectable object in theshort range must have a diameter of 2 mm. In the focus, that is at adistance of 50 mm, this value decreases to 0.1 mm. Then it starts toincrease until 3.5 mm is reached at a distance of 150 mm, the maximumsensing range (see Figure 16). Their setting is identical with the otherdiffuse-type sensors, however their sensitivity is reduced. Focussing is thesame.

In principle a change in the focus, as is the case for a camera, would alsobe possible. This would however require a very complex and precisemechanism which cannot be justified for cost and time reasons.

The laser version of the OC diffuse-type sensor for short ranges is theOCNL. As described above, the sensing range is fixed. It is between 20and 45 mm. With this sensor objects with a diameter as small as 0.1 mmcan be detected.

Focussed light beam Another option are the units with focussed light beam. Whereas, for theOFB, the focussing leads to an increase in the sensing range from 200mm (OFT) to 400 mm, the sensing range of the OLB, however, decreasesfrom 1000 mm to 800 mm. The maximum light spot diameter is reducedfrom 250 mm (OFT) to 80 mm.

Marks The sensors are often used to monitor the correct position, correctdimensions etc. of objects. For this purpose marks are applied on thematerial or marks are used that already exist. For paper processing, e.g.for printing, marks are printed on the paper to enable correct cutting ofthe sheets. For printed plastic foils or textiles the border between twofields of different colours is used. Image-creating measuring systems canalso be used for detection. The contrast sensor is an inexpensivealternative to this relatively expensive method.

Contrast sensor This unit, the OCK, evaluates signal differences. It can distinguishdifferent shades of grey. In general different colours are shown asdifferent shades of grey for monochrome detection (see 2.2.3). Thecontrast sensor can thus respond to different colours. As an exception an

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LED is used for this unit. At 565 nm it lights green (see 2.1.4). Thesensing range is programmed to 13.5 mm (see Figure 129).

Colours If the contrast sensor does not function satisfactorily, the use of the ODCcolour sensor would be an alternative. It is possible that for the contrastsensor a yellow and a light blue surface have the same grey value.Especially for multi-coloured objects it can be expected that differentcolours with the same grey values exist. The colour sensor cannevertheless distinguish these colours. The operating principle isdescribed in 2.2.3 (see Figure 130).

Diffuse reflection sensor as retro-reflective sensorIn the text above, especially in 3.4.2.3 it is mentioned that objects withgood reflective quality in the background may interfere with the diffuse-type sensor. In particular a prismatic reflector in the background wouldinterfere with the diffuse-type sensor because the exact angle ofincidence is not important here. It is however possible to invert this effectand to say the following: The variety of units can simply be reduced byusing the same unit as a diffuse-type sensor in one application and as aretro-reflective sensor in another application.

We can only advise you not to do it!

A diffuse-type sensor has to respond to less light that a retro-reflectivesensor. During production it is thus set to higher sensitivity. As aconsequence it is more susceptible to interference. It could notdistinguish between objects with good reflective quality and a reflectoreither. The use of a polarisation filter would not be possible because thiswould reduce the range. For reasons of operational reliability a diffuse-type sensor should not be used as retro-reflective sensor.

Colour sensor as retro-reflective sensor The colour sensor is an exception of the statements above. In contrast tothis, it provides a feature that is interesting for special applications. Acolour sensor used as retro-reflective sensor can for example distinguishbetween glasses of different colour.


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3.5 Fibre optics

3.5.1 Typical applications

For what? Here, once again, the advantages of photoelectric sensors:- compact

Compared to their sensing range the types are of very smalldesign. This was already the case in the past. The use ofmicroprocessors supports the trend towards more compacthousings. The use of laser diodes enables enormous ranges. Theunits become more powerful and smaller.

- reliableThey have a high immunity to interference and are also protectedagainst the ingress of water and vibrations by the use of specialpacking washers and by the full potting with a special resin. Asfor efector 100 the trend goes towards unpotted units.

- versatileSeveral units with special features exist for a number of specialapplications.

Is that not sufficient? There are always applications that are difficult to solve using the typesdiscussed so far. For some of them, listed below, fibre optic units are wellsuited.

Small objects In the past fibre optics were often the only solution. It is of course stillpossible to use them now. In the meantime laser units have become analternative to these applications so that it is no longer absolutelynecessary to select fibre optics.

Space is at a premium Even if the units become more and more compact, there are applicationswithout enough space for a complete unit. A fibre optic however canalmost always be used.

High temperatures High temperatures always influence electronics. The limit temperature isreached when the soldering paste becomes soft. Glass fibres with metalsheathing can even be used for higher temperatures (see Figure 141).

Aggressive media, oils, water Even if the units are well sealed or potted, some media attack thehousing, penetrate it, dissolve the sealing or react with the pottingcompound etc. In these applications the use of units with a plug andsocket connection is disadvantageous. In some cases this problem can besolved by the use of fibre optics with special sheathing.

Solution For the applications described efectors with connected fibre optics thatare also called fibre-optic amplifiers (OBF, OGF, OIF, OKF, OUF,) are agood solution. They are capable of conducting light to very small objectsand into very hot or very wet environments. Infrared sensors can also beused with fibre optics.

Example Figure 19 shows the basic structure of the fibre optics.

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1 glass fibres2 protective tube made of steel fibres3 metal-clad sheathing4 silicone sheathing

Figure 57: Structure of fibre optics with metal and silicone sheathing

Summary Special units have been developed for special operating conditions suchas higher temperatures, splash water or installation in places which arenot easily accessible: the photocells with fibre optics. They are capable ofconducting light into very hot or very wet environments in order to senseeven very small objects.


Photoelectric sensors with fibre optics consist of two components:¡ amplifier¡ fibre opticIt would also be possible to manufacture one compact unit containingthe amplifier and the fibre optic in one housing. This would howevermake this system less flexible. This is why here only the combination ofthese two components is offered that have to be ordered separately. Theadvantage is that a complete range of fibre optics with different sensingheads is available. You can select the fibre optic that is best suited for theapplication.They are mechanically connected via a screw connection. For glass fibresthe fibre bundles for transmitter and receiver may be of differentthickness. The sensor end pieces are mechanically coded so that incorrectuse is not possible.

Amplifier There are different types of amplifiers. Most types are either available forconnection of fibre optics or of standard lenses. Some units can be usedwith fibre optics only.

The OKF type, specifically developed for fibre optics, works with a red-light diode, i.e. visible light is emitted. This is so for the following reasons:1. The OKF type replaced an equivalent SUNX unit which also operated

with red light (OEF).2. Red light is visible, so the fibre optic can be adjusted more easily.

Red light Other amplifiers operate with red light as well. Another advantage of thered light is a smaller attenuation in the fibre optic.


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Fibre optic The material they consist of is either glass or plastic. The characteristics ofthe different materials are described below.

Sensing head This is a short overview of the different sensing heads. The completetechnical data and dimensions are given in the catalogue or in the datasheets.¡ aluminium thread: M3, M4, M5, M6, M8¡ cylindrical, made of aluminium or steel: 3.5+2.5, 3+1, 5, 6+3, 6+1,

7+3 etc. (see comments below)¡ deflection by 90°: angled (L-shaped) or cylindrical with lateral opening¡ flexible¡ with lenses: fixed or lens attachment¡ with diaphragms: to be screwed onto the unit,¡ special types: for short ranges, flat cross-section

Comments It is obvious that not every amplifier is available for every sensing head.This would be too wide a variety. The sensing heads with thread aresuited for plastic or glass. The smooth cylindrical types are only availablefor glass. They often consist of a thick stable sheath that can be used forfixing and a thinner end for outgoing and incoming light. A specialsensing head made of steel for plastic fibres has a flexible tip with alength of 95 or 90 mm. This enables easy readjustment or fineadjustment of the sensor even if the sensing head has already been fixed.However, the number of bending cycles is limited. The best solutionwould be to bend the tip only once.

Fixtures The range of accessories comprises angle supports (short ranges) or forksupports for mounting fibre optics. The advantage of the fork support isthat it is adjustable. Conventional fork-type beam sensors where thecomplete sensor is integrated in a fork support are less expensive but thedimensions are fixed.

Coupling Couplings are available for plastic fibre optics. Since they lead to anattenuation they should only be used if absolutely necessary. This is forexample the case for tool heads of a processing unit that can beexchanged. Each of these heads can be equipped with a fibre optic withcoupling so that they can simply be connected to the amplifier via thiscoupling after the exchange - similar to a plug and socket connection.

Operating principle The principle was already explained in 2.4. According to this principle therays of infrared light (OGF, OIF OUF) or rays of red light (OBF,OKF) arekept and conducted in the fibre optic. The fibre optic itself consists ofglass fibres, many with a very small diameterplastic fibres, having a larger diameter.The surrounding medium is air. It is covered by a sheath.

The transmitted or reflected light is conducted in the fibre optic by meansof numerous total reflection (see 2.4). The units function as through-beam sensor or diffuse reflection sensor as is shown in the followingfigures.

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Figure 58: fibre optic as through-beam sensor

Figure 59: fibre optic as diffuse reflection sensor

Figure 60: principle of fibre optics as through-beam sensor


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Figure 61: principle of fibre optics as diffuse reflection sensor

3.5.3 Notes on the use of fibre optics in practice

Selection It has been explained in 3.5.1 under which special conditions the use offibre-optic units is recommended. However, not every fibre optic is suitedfor every application. The following overview will help you to select theright unit.

High temperatures Use of metal-clad sheathing (...290 °C).

Wet areas Use of PVC or plastics with similar characteristics. Metal-clad sheathingshould not be used here since moisture can penetrate and wash away thelubricant.

Wet areas and high temperatures Use of metal silicone. On the one hand the metal silicone sheathing istight and no moisture can penetrate and on the other hand metal siliconecan be used up to 150 °C.

Chemicals Depending on the chemical, temperature and time of exposure metalsilicone or Viton sheathing is used.

Mechanical strain The metal-clad sheathing and the metal silicone sheathing offer a goodprotection against mechanical strain.

Below further aspects of use and selection will be explained.

Glass fibres A complete fibre optic consists of several thousands of such thin glassfibres covered with a lubricant as a slip additive to avoid breakage of thefibres. This keeps the fibre optic flexible and suitable for universalapplications. The sheathing of the fibre optics is normally made of a PVCsleeve or a flexible aluminium sheath. The plastic sheaths are suited tobeing used in "normal" environments up to 80 °C. The aluminium sheathcan be used for applications with high temperatures up to +290 °C.There is also a solution to specific applications where high temperaturesand wet environment coincide: special fibre optics with aluminium sheathin a silicone protective tube.

Glass and plastic Most amplifiers are suited for operation with glass fibre optics. Glass ismore resistant to temperature, chemical substances such as acids, alkalisand a glass fibre ages less than a plastic one, and so its attenuation isless. But one disadvantage is its high price - about 5 times as much as forplastic fibres. Also, it is more difficult to make good fibre optics fromglass than from plastic fibres. The user cannot cut them to size himself.The standard length is 600 mm. Special lengths can be manufactured onrequest.

Summary Fibre optics made of silicate glass are resistant to ageing. The sensingsurface is relatively scratch-resistant. The glass fibres do not change their

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optical characteristics during bending until they almost break. Glass fibresare chemically resistant.Glass fibres are more difficult to produce and thus more expensive. Thesensing surface must be polished. Glass fibres cannot be cut to size bythe user himself. This results in a variety of articles resulting from speciallengths.

Since nowadays plastics with improved characteristics exist, plastic fibreswere added to the product range when type OBF was launched.

Movement Plastic fibres optics have fewer fibres than glass fibre optics. Even a typewith only one fibre is available. If the fibre optic is mounted in a movingpart of the installation so that it has to follow the movement if theamplifier is fixed, it is constantly bent and stretched. The glass fibre isthus submitted to higher wear and tear. This is not caused by thebending (the minimum bending radius must of course be adhered to) butby the friction between the fibres. In this application a plastic fibre opticwith only some fibres is better than a glass fibre optic.

Fibre optics should if possible be mounted in a fixed position. Permanentmovement should be prevented. Fibre optics are not suited for dragchains, neither glass nor acrylic fibres. In hot areas movement hasparticularly negative effect since the lubricant between the fibresbecomes more fluid which results in friction between the fibres. Thesheath glass is damaged and the fibre optic is "blind".

Cut a plastic fibre to size Glass fibres should not be processed at all. Plastic fibres can be cut to sizeby the user himself. It is absolutely necessary to use a special tool that isoffered as accessory for this purpose. It must be considered that eachcutting hole can only be used once. Even a notch that cannot be seenwith the naked eye would cause considerable attenuation during the nextcutting process.

On reel For users with high demand fibres are available on reel. As accessorieswirable sensing heads can be delivered.

Summary Plastic fibres (acrylic material) are easy to produce and thus inexpensive.Optical sensing surfaces need not be polished. A clean cut is sufficient.Acrylic fibre optics can be cut to size by means of an appropriate cuttingtool. The customer can also mount the fibre optic heads himself. Acrylicfibres are available on reel. Coupling is possible (Duplex; Simplexcoupling).Acrylic fibres are not suited for hot areas. The sensing surfaces are not asresistant to mechanical strain and chemicals as glass.


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Irrespective of which material is used for the fibres the following pointsmust be observed for handling fibre optics:

1. Do not bend fibre optics - risk of breakage for individual fibres orcomplete bundles of fibres. Consider the minimum bending radius(see data sheets)

2. Do not pinch or squeeze fibre optics too tight (with fastening tools).3. Be careful with very aggressive media - special units.4. Do not subject fibre optics to too high a tensile strain. Never mount

when exposed to tension.5. Do not twist fibre optics too much.6. Do not tighten the end piece too much. Always tighten the nut, never

the end piece (risk of torsion).7. Several fibre optics on one object may interfere with each other -

observe some distance8. Fibre optics are precision units for the transmission of light. No

attempt of modification should be made by the end user (exceptionplastic).

Observe the following points when using fibre optics as through-beamand as diffuse reflection sensor: for through-beam operation the beambetween transmitter and receiver must be interrupted at least in thewhole zone A area (active zone) so that the object can be detected. Fordiffuse reflection operation the object is detected in a "conventional"manner. The maximum distance D depends again on the surfacecharacteristics of the object, on the cross-section of the fibre optic andthe incident angle of the beam on the surface (optimum 90 degrees -high reflection). The angle of reflection is a value determined by the lawsof geometrical optics and cannot be changed. The other end of the fibreoptic is connected to the suitable amplifiers (inserted and tightened) toobtain a perfect junction from transmitter and receiver to the fibre optic.

To sum up, one can say that optical sensors with suitable fibre opticsenable good and safe detection of very small objects. Relatively shortsensing ranges (depending on the object diameter) can be achieved andan exact adjustment of the two fibre optics is important when fibre opticsare used as through-beam sensors.

3.6 Light-on and dark-on mode

Output signal Before discussing the circuit in more details (see 4.1.1 and 4.2.2) theoutput signal in general is to be described first. What can be the functionof such an output signal and what does it mean for example for athrough-beam sensor?

Object Light Output Termnot present not interrupted not switched dark-onpresent interrupted switched dark-onnot present not interrupted switched light-onpresent interrupted not switched light-on

There are two different types of switching function for photoelectricsensors: dark-on switching and light-on switching. For a through-beamsensor this means:

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Dark If the light beam between transmitter and receiver is interrupted, i.e. nolight strikes the receiver and the output switches - dark-on switching unit.

Light If the light beam is however not interrupted, i.e. light strikes the receiverand the output is switched - light-on switching mode.

The same applies to the retro-reflective sensor: object present, receiverdark, output switched = dark-on switching and vice versa for light-onswitching.

And what about the third type of photoelectric sensor?

Object Light Output Termnot present interrupted not switched light-onpresent not interrupted switched light-onnot present interrupted switched dark-onpresent not interrupted not switched dark-on

The switching function is inverse to that of the through-beam or theretro-reflective sensor, i.e.:

Light This means "light strikes the receiver" = object present, output on, light-on switching

Dark No light strikes the receiver = no object present, output on, dark-onswitching

Summary of the switching functions:

Light-on switching

For through-beam or retro-reflective sensors:If the light beam between transmitter and receiver or betweentransmitter and receiver and prismatic reflector is not interrupted, theoutput is switched or the relay is energised (= normally closed).

For diffuse reflection sensors: If light is reflected to the receiver by the object to be detected, the outputis switched or the relay energised (= normally open).

Dark-on switching

For through-beam or retro-reflective sensors:If the light beam between transmitter and receiver is interrupted, theoutput is switched or the relay energised (= normally open).

For diffuse reflection sensors: If the light beam is not reflected to the receiver, the output is switched orthe relay energised (= normally closed).

Normally closed/open Sometimes the similarity with the NO or NC contact is misleading. Thisdoes not always mean:light-on switching = normally closeddark-on switching = normally openIn both cases, whether the optical (light/dark) or the electricalcharacteristics (normally closed/open) are considered, it must beconsidered whether a through-beam/retro-reflective sensor or a diffusereflection sensor is concerned.


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The different switching characteristics must be taken into account, inparticular for the selection of units if a normally open or normally closedfunction is required at the output. Not all types have a programmableoutput signal (e.g. not type OU)!

Once again Since experience has shown that in this context misunderstandings oftenoccur the context will be explained and summarised once again in otherwords.

Light/dark There are two different types of switching function for photoelectricsensors, dark-on switching and light-on switching:¡ A dark-on switching unit switches the output when no light strikes

the receiver (the receiver remains dark).¡ A light-on switching unit switches the output when light strikes the

receiver (the receiver receives light).

Through-beam/retro-reflective sensors For through-beam and retro-reflective sensors the switchingcharacteristics are thus as follows:¡ dark-on switching unit: object sensed output switched (or relay

energised).¡ light-on switching unit: no object sensed

output switched (or relay energised).If the output of the through-beam and retro-reflective sensors is toswitch (or the relay is to energise) if an object is sensed, a dark-onswitching unit must be selected; if it is to open (or the relay is todeenergise) if an object is sensed, a light-on switching unit must beselected.

Diffuse reflection sensor The switching function of a diffuse reflection sensor is inverse to that of theother photocells:¡ dark-on switching diffuse reflection sensor: no object sensed

output switched (or relay energised).¡ light-on switching diffuse reflection sensor: object sensed

output switched (or relay energised).If the output of the diffuse reflection sensor is to switch (or the relay is toenergise) if an object is sensed, a light-on switching unit must beselected; if it is to open (or the relay is to deenergise) if an object issensed, a dark-on switching unit must be selected.

An important criterion for the selection is operational reliability. Forphotoelectric sensors you have to think twice whether the normally openor normally closed function is required and if it is a through-beam/retro-reflective sensor or a diffuse reflection sensor.

It is even more confusing if you refer to a certain terminal of thechangeover contact (for amplifiers see 4.6.2) and wonder: what is thestate (High or Low) if for example object present, light-on mode,through-beam/retro-reflective sensor?

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3.7 Excess gain

3.7.1 Meaning

The operational reliability of the photoelectric sensors usually depends onthe selected sensing range, on the application and on the selected typeof unit. A good help for the selection of a certain type is provided by theexcess gain graph.

What is that? The excess gain is the ratio between the radiation actually received andthe minimum radiation required to change the switching state. Thefollowing examples will explain this.

Excess gain = 1 This is the limit value when the light striking the receiver is just sufficientto exceed the switching threshold. As for any other type of sensor thiscase is unfavourable because additional interfering factors such as soilingof the lens leads to failures.

Excess gain < 1 This case is obvious. Since the receiver does not receive enough light,switching is unsafe.

Excess gain > 1 This case is to be reached in practice. The question how much higherthan 1 the value should be depends on the application. In the case oflarge amounts of dust for example, the excess gain should be as high aspossible (see table Figure 63).

For a defined type and the same conditions the excess gain only dependson the distance. If the values are entered in a graph, an excess gain curveresults. Excess gain values below 1 need not be entered. This would notmake sense.

What does that mean? The curve in Figure 62 is a "typical" curve that shows the ratio betweenthe radiation actually received and the minimum radiation required forsafe switching of the output. This ratio was determined byexperimentation in the development labs. The shape of the graph refersto one unit type only. Please consider the double logarithmicrepresentation.

The OSR graph clearly shows a maximum value at a distance of about 2m from the prismatic reflector. Over 60 times as much light as is requiredfor safe switching strikes the receiver. This relatively high value is itsexcess gain for this particular sensing range. But a high excess gain isrequired for certain applications. As is shown in the table below, excessgain factors are really required for applications in a dusty environment,for steam, soiled lenses and/or mirrors or when the beam path can easilybecome maladjusted. So it is useful to have a look at the excess gaingraph in order to select units for certain applications.

Sensing range The graph provides more information than the range that is indicated forthe optimum case.


77

Figure 62: Excess gain curve

excess gain factor forstep operating conditions diffuse

reflectionsensors

retro-reflectivesensors

throughbeam

sensors1 clean environments, lab

rooms1 1 1

2 office rooms 2 2 for eachside = 4

1.4 for eachside = 2

3 normal industrial environ-ment, stores, workshops

4 4 for eachside = 20

2 for eachside = 4

4 industrial processes withmuch dust, haze, mist

60 60 for eachside = 3000

8 for eachside = 60

5 heavy soiling, sand blastequipment

- - 25 for eachside = 600

6 extreme soiling, mining - - 100 for eachside = 10000

Figure 63: Required values of excess gain

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3.7.2 Setting

In general it is possible to set the sensitivity of photoelectric sensors, forsome units by means of a potentiometer, for the units of the newgeneration by means of pushbuttons. The difference between thesemethods is to be explained below.

Maximum sensitivity At the factory the sensitivity (of the receiver) is set to the maximum value.The reason for this is easy to understand if you consider what a reducedsensitivity means for the graph in Figure 62. This reduction results in areduction of the maximum sensing range. Sometimes this is interpretedas a shifting of the curve to the left, towards shorter sensing ranges. Thisis however not the case. The graph is shifted downwards towards lowerexcess gain.This is why photoelectric sensors should be used with maximumsensitivity if possible.

Why change the setting? If the maximum sensitivity is the optimum as explained above, whyshould the setting be changed at all? In general the sensitivity is only setfor diffuse reflection sensors. For the other types this is normally notnecessary. In general only a diffuse reflection sensor is used to distinguishthe foreground from the background. An example: dark objects with badreflective characteristics are to be detected by the diffuse reflectionsensor, the background is a white wall.

Potentiometer By means of a potentiometer the sensitivity is set as follows:1. The potentiometer is turned until the object is only just detected.2. Then continue to turn until the wall is detected.3. The potentiometer is set to the medium position between these two

positions.

The result of this method depends on the eye, the sense of touch and theprecision of the potentiometer. Even if it were possible to find the exactmedium position, it would have to be considered that the correlationbetween the measured signal and the distance is not linear. As aconsequence this manual method cannot be the best method.

OB The OB unit offers the possibility to set the sensitivity manually, howeverby means of an "electronic potentiometer". Instead of turning thepotentiometer mechanically by means of a screwdriver, the sensitivity isset via two buttons and the help of a bar graph (row of LEDs) showingthe measured signal.

What is the optimum setting ? It was mentioned above that this question is only important for diffusereflection sensors with interfering background. The sensor is todifferentiate an object from its background as reliably as possible. Let ustake the example of an OBF as diffuse reflection sensor showing themeasured signal.

Object In an application a signal value of 5 is read out for the detection of theobject. The scale is not important here. Just imagine that the result doesnot depend on the used scale. If you prefer to be more specific, you canalso imagine the signal to be 5 V.


79

Background The background provides the measured signal value 1. This should notaffect the safe detection of the object.

"Medium" In case of manual setting, whether by means of an electronicpotentiometer such as for OB or a mechanical one for other units, themedium position is selected (see description above or 3.4.2.2). So tospeak, the switch point is set to 3. This value corresponds to thearithmetical mean:

( 5)2

21 fffa

õã

The difference, the distance between 1 and 3 or between 3 and 5 is thesame, that is 2. But it is not the difference that is important here but thefactor.

Factor 3 If the background signal is (1) and the switch point is (3), we need asignal that is three times as high to be protected against interferencefrom the background.

Factor 1.67 If the object signal is (5), this is only 1.67 times the switch point (3). Arelatively small amount of soiling would already lead to uncertaindetection of the object.

When the unit is set to the "medium position", the excess gain factorwith regard to the background is higher than that of the object.

1 Object2 Switching point3 Background

Figure 64: centre position

What is a better solution? The task is to find the point where the excess gain factors with regard tothe object and the background are the same:

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or transformed:

( 7) 21fffg ã

fg has the index g because this formula is also called geometric mean.

2.24 For this example the result is approximately fg = 2.24. This is the optimumswitch point at which the excess gain factors with regard to object andbackground are the same.

Automatic setting is better Now it becomes clear why the automatic setting is better. Apart from thealready mentioned fact that the display of the OB and the setting byturning the potentiometer are not very precise, a root must be calculated.This is very easy by software but only few people are still able to calculatea root mentally.

Dynamic measurement Another aspect is that in practice the process cannot always be stoppedonly to adjust a diffuse reflection sensor. If objects continuously pass it,the measured signal continuously changes between the value for theobject and that for the background. If this happens rapidly, a manualsetting is no longer possible.

3.8 Switching frequency

The switching frequency of a photoelectric sensor depends on a numberof parameters¡ Operating principle (through-beam, retro-reflective, diffuse reflection

sensor)¡ Measures to increase operational reliability (see 4.1.2)¡ TypeOther parameters are the characteristics of the components and thecircuit which together constitute the switch-on and switch-off delay.Their influence on the switching frequency, however, is comparably smallso that we do not go into detail here. Due to the large number ofinfluences general statements can hardly be made. A more detailedexample is given in chapter 4.1.2, example OF. The switching frequency isindicated in the data sheet of the respective sensor.

What for? In practice an application defines requirements and the sensor whichmeets these requirements has to be found. Given are for example thesize of the objects and the gaps between them as well as the travelspeed. In the following it is described on the basis of examples how aguide value for the required switching frequency is determined usingthese values. A counting job is a typical example.

Caution! It should, however, be mentioned that these values are estimates. If forexample a required switching frequency of 100 Hz is determined a sensorwith a maximum switching frequency of 100 Hz should not be chosen.This would be in the limit area and thus increase the risk of incorrectswitching. In this example a sensor with a switching frequency of 500 Hzwould be preferable.


81

Operational reliability In general, it has to be taken into consideration that the faster an opticalsystem, the more it becomes sensitive to extraneous light. A photoelectricsensor using constant light reacts faster to an interruption of the lightbeam than a comparable unit using pulsed light. Here a given amount oflight pulses must have reached the receiver before the output switches(see 4.1.2).

Switching frequency Photoelectric systems detect the entry of an object into the beam pathand its exit from the beam path virtually without delay. However, it takesa certain time until they signal the light modification by a change of theswitching status. The switch-on (=mark) plus the switch-off (=space)times determine the switching frequency of the system. A mark-to-spaceratio of 1:1 is taken as the basis for its determination.Therefore it has to be verified if the system can safely detect the objects,especially¡ when the objects quickly move past the unit,¡ and/or when the objects (or the gaps between the objects) are very

small.

Here two cases have to be differentiated:1. The pulse frequency is constant and the mark-to-space ratio is 1:1.

In this case the following applies: The indicated switching frequency ofthe unit has to be at least as high as the object frequency (or the spaces).Example: Objects with a length of 10mm and a spacing of also 10mm(object to object) are to be detected on a conveyor belt. The objectsmove at a speed of 1000mm/s.

St = smminspeedtransportmaximummminlengthpauseorlengthobjectx/

2

The required switching frequency is thus:

f = st1

This results in:

st = mm/s1000mm10x2

= s501

f =

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= Hz50

The switching frequency of the unit, indicated in the data sheet, has tobe at least 50 Hz.

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2. The mark-to-space ratio is not constant and the marks / spaces differsignificantly (small objects and long spaces or large objects and shortspaces).

In this case a unit has to be chosen whose switching frequency still allowsto safely detect the smallest pulse length or the shortest pause length.A pulse (a space) has to be followed by a pause (a mark) of the samelength.Example: Objects with a length of 10mm and a distance of 5mm (objectto object) are to be detected on a conveyor belt. The objects move at aspeed of 1000mm/s.

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2

The required switching frequency thus is:

f = st1

This results in: t(s)= 2x5[mm] / 1000[mm/s] = 1 / 100[s]f = 1 / 1/100 = 100 Hz

The switching frequency of the unit, indicated in the data sheet, has tobe at least 100 Hz.


83

4 Examples of photoelectric sensors

4.1 Technology

4.1.1 Circuitry

Processing and evaluation of signals What happens in the photoelectric sensors electronically?

Figure 65: Block diagram through beam sensor

Through-beam sensor The block diagram shows the functioning of a through-beam sensor. Thetransmitter unit contains the power supply, the cycle generator and thetransmitter. Today a transmitter diode is used. The transmitter diodeemits light (IR or red) in cycles. Cycling ensures longevity of the LED andat the same time high performance at low current consumption. Thecycle frequency is 5 to 10 kHz, the ratio on/off approx. 1/100. This meanslong recovery times for the transmitter diode.

Wear and tear A big advantage of semi-conductor elements such as the transistor istheir wear-free functioning. LEDs are an exception. They are submitted toageing. This means that the longevity depends on the duration ofillumination. This is why long recovery times are advantageous.

The phototransistor or the photodiode of the receiver receive this lightwhich is electronically amplified and via an evaluation stage supplied tothe output stage which then switches. Many units provide differentpossibilities to program the output stage.

Noise suppression Noise suppression is of course essential for photoelectric sensors to avoidincorrect switching. The first two points of the following list refer to anysensor, the third point is a special feature of the through-beam sensor.¡ shielding of the circuit against high-frequency electromagnetic fields

which interfere from the outside¡ skilful design layout to avoid interference within the circuitry

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¡ For the through-beam sensor a high-pass filter in the receiver ensuresthat only high-frequency signals from the cycle generator of thetransmitter are accepted by the receiver and amplified. So thisexcludes interference from extraneous light, e.g. the 100 Hz flickeringof a fluorescent tube.

In the past the 20-turn helical potentiometer for the accurate sensitivitysetting of the receiver was available in almost all designs (for example forthe safe detection of partly transparent objects). Today the newlydeveloped units are set (programmed) by pressing a button (see 4.3).

Retro-reflective sensor For the retro-reflective sensor all functional units are contained in onesingle unit. Compared to the through-beam sensor this is a bigadvantage with respect to noise suppression.

Figure 66: block diagram retro-reflective sensor

Noise suppression The better noise suppression becomes obvious when the signal sequenceis followed through step by step: power supply, cycle generator,transmitter sends cycled light, two possibilities:1) Object not present, light strikes the receiver, preamplifier amplifies atthe same cycle (i.e. gate circuit), the signal received is evaluated, theoutput does not switch.2) Object present, the receiver receives no light, the receiver amplifier isactivated at the same cycle as the transmitted signal and the "no receivedsignal" is fed to the programmed evaluation stage (light-on/dark-on), thesignal is fed to the output stage and the output switches on or off,depending on normally open or normally closed operation.


85

Figure 67: block diagram diffuse reflection sensor

Diffuse reflection sensor When comparing the block diagram of the diffuse reflection sensor withthat of the retro-reflective sensor no difference can be seen. The onlydifference is that the light is not reflected by a prismatic reflector but bythe object itself. In 3.4 it was already mentioned that the tuning of thecircuitry is however completely different. The diffuse reflection sensormust respond to an intensity of light that is only a fraction of that of theretro-reflective sensor. This cannot be represented in a simple blockdiagram.

4.1.2 Operational reliability and failure warning

In 3 we have already discussed the influences that may lead tomalfunctioning of the photoelectric sensors. The methods to prevent thiswhich are described in this chapter will be summarised and completed.

Frequency filter Extraneous light can either have permanent influence on the receiversuch as the light of a bulb or it has a certain frequency such as the 100Hz flickering of a fluorescent tube. This interference can be prevented byappropriate circuitry, such as a high-pass filter.

Gate circuit If the receiver is only active when the transmitter is active, even intensiveinterference such as by a flash can be prevented. For continuous solarradiation this method is not so effective.

Analogue These two methods have one thing in common, they are analogue. Inmodern technology it is of course obvious to complete or replace themby digital methods.

Digital The first step on this way is to count the pulses. The description howfailures can be detected by this method follows below.

Future Another step will be that the transmitter emits certain pulse sequencesand the receiver "learns" to evaluate these pulse sequences only. This isalso a solution to the problem described in detail in 3.2.2, that is themutual interference of several photocells.

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Let us now go to the technical implementation.

The OV 310 / OV 110 amplifiers feature a digital noise suppression whichincreases the operational reliability even more.

Figure 68: digital noise suppression 1

Figure 69: digital noise suppression 2

Via the pulsed transmitted light the signals which are reflected by theobject or the reflector reach the receiver as pulses. For the other designsthese signals are integrated over a certain period and compared with athreshold value (adjustable by means of a potentiometer) at theevaluation stage, the output then switches accordingly, that is ananalogue method. For the OV type this process is digitised.

6 pulses The evaluation stage waits until it receives 6 consecutive signals of theother switching status and changes the output signal at this moment. Soit is almost impossible that interference from optical or electricalinterfering pulses from the outside affect the switching status as long asthey do not interfere at least 6 consecutive times at exactly the samecycle frequency.


87

Switching frequency The price to pay for the gain in operational reliability is a reduction of theswitching frequency. The shortest possible period is 2 x (time for 6pulses), see below, example OF.

Function display The units which are made in such a way (apart from the OV type also theOP which is no longer available today) also feature a special switchingstatus display. This display is not only capable of indicating whether theoutput is on or off but it also flashes at 2 Hz or 10 Hz. The flashingdisplay serves as a setting aid for finding a safe working range and alsowarns of interference or soiling on the lenses. ifm holds a patent for thiskind of 4-function display in one LED:

Figure 70: function display

The table shows the possible displays and their meaning:¡ flashing at 10 Hz: always unsafe area, but the output has switched,¡ 2 Hz: always interfering area, the output has not yet switched.¡ permanently lit LED or an off LED: switching status of the output in

the safe area (depending on light-on or dark-on switching function).

The following figure shows the flashing signals when an objectapproaches or moves away from a light-on switching diffuse-type sensor.The typical hysteresis range of the diffuse-type sensor can also be easilyseen.

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Figure 71: pulse diagram function display

4 states The binary standard sensor can only provide two pieces of information(0,1):¡ object detected¡ object not detected

It is obvious to use another bit for the additional two pieces ofinformation, that is to provide the unit with a second output for functioncheck. With 2 bits 4 states can be distinguished (00, 01, 10, 00):¡ object detected (certain)¡ object detected (uncertain)¡ object not detected (uncertain)¡ object not detected (certain)

Meaning The states can exist for different reasons. Typical failures of photoelectricsensors are caused by soiled lenses or by interfering backgroundreflection."object not detected (uncertain)� means: not all pulses emitted strike thereceiver. This is for example caused by soiling."object detected (uncertain)� means: individual pulses strike the receiver.These pulses can be interfering background pulses.

Failure warning If the function check signal of the output is "uncertain area", this canalso be called a failure warning. Such messages can help to avoidexpensive standstill or frequent maintenance. Simply by cleaning the lensat exactly the correct moment, failures in the process can be avoidedbefore they arise without stopping the process. If you wait until a failureoccurs, considerable costs can result.

Function check Type OA was the first type to provide a function check output as astandard. Its signals can for example be passed on to a plc input. This canfor example cause the following measures:"unsafe state� - lens is soiled � open compressed air nozzle in front ofthe lens � clean lens � "safe area" � close compressed air nozzle, possiblyadd the following: safe state not reached after 1 min - give alarm. For the


89

new units the function check output can be selected as an option or iseven provided as a standard (see 4.2.2).

Why not always? If it is so easy to increase the operational reliability, why not use unitswith function check output only?This has several reasons.This message has to be processed correctly by the controller. It must betaken into account that the unsafe state is always passed when theobject enters the beam. Moreover it could also remain in the unsafe areawhere the beam is only partly interrupted. The programmer must thinkabout it carefully to avoid too frequent cleaning or alarms.The connection of an additional switching output to the plc meansadditional wiring effort. Moreover an additional plc input is used. For onesensor this is not important. But in many cases dozens or hundreds ofsensors are used. This is the reason why the function check signal is onlyused in critical cases.

AS-Interface The last point becomes less important if a modern technology such as theAS-interface is used. If the system is not completely used and this isalmost always the case, a binary sensor can easily be replaced by a so-called intelligent sensor that can provide additional information to thecontroller via the same cable.

Standard More and more new types offer the function check output as a standard.It is then up to the user whether he uses this output or not.

Test input Some units also have a test input (see 4.2.2). If a signal is provided at thetest input, the transmitter is switched off. The output must then invert itsstate if it functions correctly.

Current example OF The problem could be clearly described at the example of theconventional technology. A similar principle is used for the more recentunit generations. Some details are different. As an example thecorresponding characteristics of the OF are explained in detail.

Transmitter The OF system operates with pulsed infrared light. The pulse frequency is3 kHz, a pulse with a length of approx. 14µs is transmitted every 500µs.

Signal reception The signal reception is also controlled via the pulse frequency of 3 kHz(this results in 2000 detection cycles per second).¡ input pulse detected 6µs after the end of the transmitted pulse = opto

contact (light pulse received)¡ no input pulse during the 6µs = no opto contact (no light pulse

received)

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Evaluation of the signals The OF does not only detect whether an input signal has been receivedbut it also evaluates its intensity and differentiates between 4 classes ofinput signals:

Signal Output Range 1 no signal output not switched Range 2 unsafe signal output not switched Range 3 unsafe signal output switched Range 4 safe signal output switched

Switching frequency However, a switching operation only takes place if two successive signalsof the same range have been detected (e.g. 2 signals in range 4). Thisleads to an increase in noise immunity.As 2 detection cycles are required for both the switch-on and switch-offoperation the theoretical switching frequency (for 2000 detection cyclesper second) is 500 Hz.

Signal processing and indicationLight-on mode Dark-on mode

Signal Output Signal OutputSignal inrange 1

LED red OFF OFFLED yellow OFF

LED red OFF ONLED yellow ON

Signal inrange 2

unsafeLED red ON

OFFLED yellow OFF

unsafeLED red ON

ONLED yellow ON

Signal inrange 3

unsafeLED red ON

ONLED yellow ON

unsafeLED red ON

OFFLED yellow OFF

Signal inrange 4

safeLED red OFF

ONLED yellow ON

safeLED red OFF

OFFLED yellow OFF

Function check output (only for connector units)The function check output signals external and internal faults. Externalfaults are e.g. soiled lenses, maladjustment.The OF counts safe and unsafe signals and compares their number. Itdetects external faults and sets the function check output if¡ at least 256 unsafe signals (range 2 and 3) occur in one evaluation

cycle (=4 s) and¡ the number of unsafe signals (range 2 and 3) is greater than that of

the safe signals (range 4).If there are less than 256 unsafe signals within the evaluation cycle or iftheir number is below that of the safe signals the counters are reset.Thus faults are reliably detected but faults which only last for a shorttime (e.g. transition from damping to undamping) are not displayed. The function check output is reset if more safe signals or less than 256unsafe signals occur within an evaluation cycle, i.e. it is reset at theearliest 4 s after an object has been safely detected again.

In addition to faults which occur due to the optical operating principlethe function check output also indicates faults in the electrics, e.g. shortcircuit, or of the (own) electronics. In order not to stray too much fromthe topic of the function check output these functions are briefly


91

described here. Thus a few points from 4.2 already have to be mentionedhere.

Internal faults (short circuit in the switching output)¡ The function check output is set, at the same time the LEDs signal as

follows: The red and yellow LEDs flash alternately at about 3 Hz (forcable units the yellow LED flashes at this frequency).

¡ The switching output opens.¡ The normal evaluation program is interrupted.¡ The switching output is cyclically detected (1x per second).If the short circuit has been rectified the OF returns to its normalevaluation program after about 1 s and resets the function check output.

Internal fault (evaluation electronics) In case of a fault in the internal evaluation electronics the function checkoutput is set. In addition, the LEDs signal:The red and yellow LEDs flash alternately at about 1 Hz (for cable unitsthe yellow LED flashes at this frequency).After the fault has been rectified the function check output is reset andthe OF starts a new evaluation cycle (i.e. normal function approx. 4 safter rectification of the fault).

4.2 Current and voltage ranges

The photocells can be supplied as DC, AC or universal current units. Theycan be used over large voltage ranges, so all customers' requirements canbe met. The figure below shows the individual current types for thesupply voltage (current) available.

under construction

Figure 72: unit family

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4.2.1 Leakage current, minimum load current and voltage drop

Connection technology For a detailed description please see the corresponding training manuals.Here we will only briefly discuss one aspect which is especially importantfor photoelectric sensors.

UC Note that it is normal for the 2-wire universal current units that a leakagecurrent of up to 6 mA (OI) constantly flows to keep the unit ready foroperation. If such a unit is directly connected to a plc, this may lead toproblems if the inputs of the plc are of high impedance and the currentsupply of the units is thus no longer sufficient. When using such 2-wireunits the voltage drop of up to 10.5 V (already possible at 24 V DC andhigh load, OS) must be considered. If the leakage current then no longersuffices for a certain load, the voltage drop can be reduced or the ratioleakage current to load current can be improved by connecting a resistoror an R-C combination.

AC The same goes for the 2-wire AC units, their values are, however, notquite so extreme (e.g. 6 mA, 7.5 V). When problems arise for thesereasons, it should always be checked whether easy-to-use 3-wire DC orAC units fitted with a signal wire of their own can be employed.

Figure 73: additional resistor

4.2.2 Connection

With regard to the switching functions the output circuits are similar tothose of the other sensor types and need not be repeated here.

Current consumption Please remember that the current consumption, that is the current thesensor requires for its own functioning, is higher than for the inductive orcapacitive proximity switches because light has to be generated.Especially for the use of photoelectric sensors the correct power supplymust be selected to guarantee reliable functioning.

Moreover we would like to remind you of the fact that the light-on ordark-on mode describes the optical characteristics and is not equivalentto the electrical function "normally open" or "normally closed" (see 3.6).


93

In Figure 78 and Figure 79 the normally open or normally closed symbolis used for simplification but the switching function is different forthrough-beam/retro-reflective sensors and diffuse reflection sensors.

In addition photoelectric sensors have special features which aredescribed below.

The connection of the through-beam sensor is described in details. Thesame applies however to the retro-reflective and diffuse reflectionsensors.

Through-beam sensor For the through-beam sensor two units have to be connected (see 3.2).

Transmitter In general the transmitters are 2-wire units because they only have to besupplied with current. For almost all cable or plug-and-socket units Figure74 can be used as a reference.

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Figure 74: Wiring diagram through-beam sensor transmitter

For the units with terminal chamber the wiring is given in the data sheet.The OA is given as an example.

Figure 75: Wiring diagram OAS

Test The OC and OA units have a simple test function. If voltage is applied tothe test input, the transmitter is switched off during this time. If thesystem is intact, the output signal must be inverted. For a through-beamsensor it is the transmitter that is provided with the test input. These unitshave 3 connections (white cable, marked WH, or pin 4 for OC; terminal 5for OA) (unlike Figure 74).

Figure 76: test input for OAS

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Caution! If an incorrect socket is used, the test input of the unit can be disabled. Incase of a jumper between the respective pins, voltage is applied to thetest input permanently. The transmitter is then permanently switched off.

Receiver The variety of types is so great that not all versions can be listed here.

Semi-conductor output The variants of the OGE are presented as an example of units with semi-conductor output.

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For UC units the receiver is also a 2-wire unit. For the connection of theload please see 4.2.1.

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Figure 79: Wiring diagram through-beam sensor receiver DC npn

Function check output Like many other units the DC units are 3-wire units. Figure 78 and Figure79 show a special feature. In addition to the normal switching outputsome units have a function check output (abbreviation fc). Almost allunits of the new generation provide this function. For some types onlythe units with plug and socket connection provide this feature. Sometypes have two variants, with and without function check output. Even ifthe unit has a function check output as a standard, it is up to the userwhether he uses it or not. See also 4.1.2. Here the conditions for aswitching of the function check output are described at an example.

The function check output enables the monitoring of the unit by meansof a controller. It provides max. 10 mA. For programming please take intoaccount that in many processes the object passes an unsafe area before itis safely detected or not detected. The installation instructions of the OGdescribe the characteristics of the output:

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OA The function check output of the OA oscillates in case of a failure (5 Hz).Figure 80 shows the terminal connection of the OAE with semi-conductoroutputs.

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Figure 80: wiring diagram OAE

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The output provides an oscillating signal, e.g. when the lens or thereflector is soiled. A signal such as in Figure 81 is provided if for examplea cloud of vapour passes between the object and the receiver. Theswitching output does not change its state.

Relay The OL also offers the relay output option.

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Figure 82: relay output

For the OA with relay output the 5th terminal is also used. It is a relaywith changeover contacts.

Retro-reflective sensor The general characteristics are described in 3.3. For many units the wiringdiagram is equivalent to that of the receiver of the through-beam sensor.

The UC units are 2-wire units (see Figure 77). In particular, it must betaken into account that the residual current can be higher, e.g. for theOS up to 8 mA (see 4.2.1).

Most DC units are 3-wire units. Figure 78 or Figure 79 can be used as anexample. The above-mentioned information on the function checkoutput of the through-beam sensor also applies to the retro-reflectivesensor.


97

The wiring diagram for the relay output of the OL (Figure 82) is alsoequivalent to that of the retro-reflective sensor.

Diffuse reflection sensor As regards the switching output there is almost no difference between adiffuse reflection sensor and a retro-reflective sensor. The difference withregard to dark-on and light-on mode must be taken into account.

Fibre optic amplifier For these units the switching function is programmed via theconnections, such as in Figure 79.

4.3 Handling

This chapter gives a short overview of the many functions available forthe user. In many cases this concerns the setting of the sensitivity. Sinceother functions such as timers are also concerned, the term handling wasselected for this chapter.

4.3.1 Setting of the sensing range

We would like to mention once again that the sensitivity of the through-beam sensor and the retro-reflective sensor should almost never bechanged. An exception is the detection of partly transparent objects.

Automatic setting Since the manual setting is no optimum solution (see 3.7.2) and in thefuture almost no new unit will offer this option, it will not be coveredagain here. General descriptions which do not refer to a specific unit canbe found in 3.7.2. The automatic setting is described with examples. Forother units the procedure is similar. Such a procedure is often calledTeaching or Teach In.

Where can the instructions be found? The installation instructions parts of which are given below are enclosedto the respective units. They are also available on the internet.

Exemplary Since everyone has access to the instructions, only the setting of the OGis described in more details as an example.

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4.3.1.1 OG as through-beam sensor

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Figure 83: OGS, OGE

Since the setting of the through-beam sensor is rare, it is not describedhere. The procedure is almost the same as for the retro-reflective sensorthat is described below. The difference is that for the through-beamsensor it is the receiver that is set.

4.3.1.2 OG as retro-reflective sensor

Partly transparent Even if it is rarely the case in practice, we will show the setting of theretro-reflective sensor to a partly transparent object to complete thepicture.

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Figure 84: OGP

For static objects the position of which can be changed, the procedure isas follows:


99

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* The * in Figure 85 means that the order is not important. You can alsoproceed in reverse order.

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Figure 86: OGP dynamic objects

As already mentioned one of the advantages of automatic setting is thatit enables setting for moving objects (Figure 86).

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4.3.1.3 OG as diffuse reflection sensor

Background For diffuse reflection sensors interference by the background is possible.In practice it is better to use a unit with background suppression. In caseswhere this is not possible, e.g. because of the shorter range withbackground suppression, it can however be necessary to set the range.

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Figure 87: OGT

The following instructions show the similarity to the above-mentionedunit (4.3.1.2). We can assume that if you can set one type you can alsoset all the other types.

Static A difference is again made between static and dynamic objects. First ofall, the setting of a static object is described.


101

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Order Here it is also possible to proceed in reverse order.

Dynamic The procedure for the setting of dynamic objects follows.

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Figure 89: OGT dynamic objects

4.3.1.4 OGH as diffuse reflection sensor with background suppression

The difference between the OGH, the OG diffuse reflection sensor withbackground suppression, and the simple diffuse reflection sensor OGT isthat a PSD is used as receiver. This is an elegant way to implement abackground suppression (see 3.4.2.3). The setting is almost identicalwith that of the OGT. This is one advantage of this technology. The userneed not learn complicated handling functions, he can proceed asalways.

4.3.1.5 Displays and other settings

Displays In the chapter of the wiring diagrams (4.2.2) the function check outputwas also described. Even if it is not used or not available, the unit itselfindicates the unsafe state (red LED). More pieces of information than justthe switching state are indicated. The following table gives an overview:


103

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Display of the OF For the OF there is a difference between cable units and units with plugand socket connection. However, the LEDs provide functions similar tothose of the OG.

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The following table shows the functions:

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No switching threshold In all cases, static or dynamic objects, through-beam sensor, retro-reflective sensor or diffuse reflection sensor, automatic setting of theswitching threshold may not be possible. As regards the retro-reflectivesensors the objects can for example be so transparent that a detection bya retro-reflective sensor is not possible. In this case the red LED flashesafter step 4 or 5. The switching threshold then remains unchanged. Thisis no special disadvantage of the automatic setting. In such a case manualsetting would not make sense either.

Prevention of unintentional setting Normally the sensitivity should not be changed. Even if a switchingthreshold was set, as in the above-mentioned special case, it might occurthat safe functioning can no longer be guaranteed because the switchingthreshold is changed by improper handling, playing with the settingbutton without knowing the functions. There is one thing we can do toprevent this.

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Latching The unit can be latched so that the switching threshold cannot bechanged.

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Figure 91: latching

Maximum sensitivity As already mentioned, this is the optimum setting especially with regardto the excess gain. If a unit was nevertheless set, an option to reset itsinitial state would be interesting.

Initial state This procedure can also be called reset or setting of the default values.The procedure is as follows:¡ Pass into the programming mode (step 1 in Figure 85)¡ Align the unit in a way that no light is reflected¡ Press the setting button twice (steps 2 and 3 in Figure 85)

Laser The setting principle of the laser units is similar to the units with an LEDas emitter of light. During setting the intensity of the emitted light isincreased to facilitate installation. It is easier to see the light spot. Thisfunction which is also called setting aid is preset in the program of theprocessor. The user need not learn any new operating function.

Setting aid There is one small difference between a standard through-beam sensorand the laser version because of the setting aid. Here not only thereceiver can be set as described in 4.3.1.2. In order to activate the settingaid, the transmitter also has a button and LEDs for indication.

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Figure 92: OGSL

The easy handling is described in the following Figure 93:


105

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OA The first unit with standard function check output was the OA. Asdescribed in 4.1.2, this function enables the monitoring of the unit and afailure warning. The red LED indicating the function check can also beused for mounting.

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Figure 94: OAR

The example of the OAR, Figure 94, shows the three LEDs of the unit. Inaddition to the standard LEDs, green for "ready for operation" andyellow for the switching state, the red LEDs can also be used formounting.¡ The red LEDs light in case of accurate alignment¡ The red LEDs flash in case of inaccurate alignment

OJ The output function of the OJ type can be programmed.

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Figure 95: Output function OJ

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4.3.2 Timers

Timers, for what purpose? Since any timer function can be achieved by means of an electroniccontroller and sensors are normally connected to such a controller, thisquestion is justified. The answer is to be summarised briefly.¡ decentralisationThe current trend in automation technology goes towardsdecentralisation. Among others this is to reduce standstill times. If thecomplete process is controlled by one central controller, it is completelystopped if this controller fails. In case of a decentralised system with asuitable reserve, parts of the process can be continued even if oneprocess step is interrupted.¡ further supportThis general trend mainly concerns the controller, not the sensor. Even orperhaps especially if a small decentralised controller is concerned, it isbetter to relieve the controller of such standard functions such as timerfunctions. If the sensor assumes this task, the program and thus theresponse time are shorter.This becomes obvious if you take into account that the timer functions ofthe sensors correspond to the standard timer functions used for theprogramming of a plc. The pulse delay prevents the effects of inputchattering whereas the pulse stretching guarantees safe processing ofpulses even with a slow controller. Especially the delay can only be set atthe sensor in this case. This also explains why the timer function diagramsof different units are almost identical. Almost the same functions arerequired again and again. The different types of setting result from thedifferent hardware versions.¡ settingIn many cases the easiest and most effective way to change a parameter,here the timer, is to observe the process directly on site. This means thatthe easiest way is for example to change the setting of the sensor directlyon site and not while sitting in front of a monitor somewhere else.


107

OS One programming feature of the OS is to set an on or off delay for theoutput signal or to program that the output signal is always given as apulse of the same length. The respective delays can be continuously setfrom 0.01 to 5 seconds by means of a second potentiometer on the unit(see Figure 96).

Figure 96: timer functions of the OS

The amplifier type OV 310 also offers the feature of on and/or off delayand pulse delay. The on and off delays can be set separately between0.03 and 10 seconds by means of two potentiometers and can beselected simultaneously or separately. For pulse delay the pulse length forthe on delay can be set by means of a potentiometer (see Figure 97,Figure 127, and 4.6.2).

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Figure 97: timer and output functions of the OV 310

Old and new The size of the OS and the OV 310 already shows that analogue circuitryis still used. The units of the new generation however have a processorwhich enables the same functions in much smaller housings (as for OB).

OB The next unit covered is the OB. Its display is of particular interest. The OBcould have been mentioned in chapter 4.3.1.5 as well but was omitted toreduce the length of the chapter. Among others the display of the OBshows the intensity of the signal. We will not present the display in moredetails here. An example of how the display can be evaluated is given in3.7.2.

Practical experience has shown that in only some cases this display wasabsolutely necessary. This is why only the OB has this display. If one day aunit displaying the measured value is necessary, it will rather have an LCDdisplay. The resolution of a row of LEDs is not precise enough. It isdefined by the number of LEDs. The option of manual setting, "electronicpotentiometer", was only rarely used either. The new units offer thefeature of automatic setting. A display would not follow the currenttrend to manufacture more and more compact and small housings.


109

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This chapter covers especially the timer function. For the setting of thesensitivity please see the installation instructions.

In a relatively small unit it is not so easy to integrate a display and theoperating buttons in a way that free programming of the time within aninterval is possible. This was one reason why two LEDs were integrated inone window so that we actually have two rows of LEDs. The delay can beset according to the following instructions:

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Training manual

110

OA This type still belongs to the generation of units with analogue circuitry.The dimensions or the volume of the unit already show this. As an optionthe OA provides a timer function which is set on the back of the unit:

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Figure 100: setting of OA

The type of timer function is given in the following diagrams:

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OAH This type also offers a timer function as an option. It is equivalent to thatof the OA. The timer diagrams, Figure 101 and Figure 102, are the same.The setting is slightly different:

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Figure 103: setting of OAH

The meaning of the switch position is given in the following table:

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Training manual

112

4.4 Mechanical properties

4.4.1 Designs and ranges

The range is actually no mechanical but an optical property. But since it isrelated to the design, it makes no sense to treat this feature separately.

4.4.2 Mounting

Is this important? You can take the following view: The manufacturer supplies a completerange of products. Cylindrical with thread, rectangular with holes forscrew fixing, bases to be mounted separately for placing the electronics(OL), etc. Mounting is then the user's job. But specially with photoelectricsensors precise alignment is specially important, see for example 3.2.2.Due to the use of laser sensors this point becomes even more important.

Much time and cost This would lead to a paradoxical situation for the user. He obtains sensorsas series units, possibly in higher quantities and then has to make thefixtures on his own, which involves much time and cost. Time and cost isspecially high if the fixtures for precise adjustment must be developed bythe user.

System But nowadays the notion of system becomes more and more important.The user does not only need the sensor as an individual componentwhich is adapted to his system but a sensing system which is ready foruse. The mounting accessories do not only complement the range ofsensors but are important system components.

A first step in this direction was the development of a mounting set forthe type OG and angle brackets for the type OL.

OG An essential part of the mounting set is the patented clamp whichenables easy adjustment in any direction using an angle bracket. Thesensor is fixed by tightening one screw only. The two three-dimensionalangles can be adjusted as required. In addition, an adjustment unit forlaser sensors is also available.

OL When the angle brackets for OL were developed the typical application ofthe design was taken into account. The typical OL application is tocontrol and monitor conveying processes. The sensor is to detect objectson a conveyor belt. With many moving objects the risk of a mechanicaldamage to the sensor is higher than in other applications. This is whyspecial angle brackets with protective shroud were developed.

Universal These solutions were intended for some designs. The next step was todevelop a system for easy mounting for as many designs as possible.Such a system must consist of as few components as possible to ensureclear and easy handling.


113

Mounting arrangements First, the mounting types used in practice were analysed. It was foundout that there are mainly three types of mounting.

Rod Many people use rods for mounting photoelectric sensors. When themechanical layout of a plant is planned their use is intended right fromthe start. The clamp was developed for this type of mounting.

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Figure 104: Clamp and rod

Surface The sensors are also often mounted on a smooth surface, e.g. on ahousing, a cover, etc. With few additional components rod mounting ispossible again. The user only has to drill a hole into the surface.

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Figure 105: Surface with rod and clamp

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Training manual

114

Aluminium extrusion The aluminium extrusion is a frequently used component. To be able touse rod mounting again a cube type mounting component wasdeveloped. Since the actual cube (c) with the threaded hole shown inFigure 106 can be oriented in different directions another flexible anduniversal type of mounting was implemented with few components.

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Figure 106: Aluminium extrusion with cube

With the fixing screws (b) in Figure 106 the cube can be adapted tovirtually all extrusions and also to almost every slot.

Similar to free standing mounting, mounting is again adapted to the rod.

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Figure 107: Cube on the aluminium extrusion with screw


115

The clamp is fastened again around the bolt.

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Figure 108: Aluminium extrusion and clamp

The following figures illustrate the versatility of the mounting system andwhat is meant by adapting free-standing and aluminium extrusionmounting to rod mounting with clamp.

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Figure 109: Rod for the aluminium extrusion

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Training manual

116

Crank It can be seen in Figure 109 that this type of mounting poses no problemwhen the rod is longer than the aluminium extrusion. If this is not thecase, i.e. more space is required for the clamp, a crank-shaped rod can beused.

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Figure 110: Rod (crank) with aluminium extrusion

How is the sensor mounted? In the figures no sensor has been shown so far. The goal was to showthat the mounting system is universal, i.e. virtually suitable for mountingevery sensor type. Only the mounting of the sensor itself requires specificparts, the angle brackets. The following section gives examples, detailsare given in the data sheets.


117

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Figure 111: Angle bracket (1) and clamp

The sensor, here at the example of the type OG, is fixed using the anglebracket.

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Figure 112: Sensor and angle bracket (1)

2 fixing angles The clamp can be turned around the rod (of course before it is fixed with(b)). On the clamp the angle bracket can be adjusted to any angle. InFigure 112 the sensor can be adjusted to the bottom and to the side. Theangle bracket as well as the clamp are fixed by means of (b). With thiseasy and quick mounting the sensor can be oriented to any direction.

The system is complemented by more angle brackets which can virtuallymeet all requirements.

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Training manual

118

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Figure 114: Angle bracket (3)

Laser sensors Precise alignment is specially important for laser sensors. There is a specialangle bracket which enables fine adjustment.

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Figure 115: Angle bracket for fine adjustment


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Figure 116: Angle bracket for fine adjustment with the sensor

Other sensor types are mounted by means of other angle brackets.

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Figure 117: Angle bracket for OL

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Figure 118: Angle bracket for OL with sensor

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Training manual

120

This example shows the angle bracket with protective shroud.

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Figure 119: Angle bracket for OL with protective shroud

Prismatic reflector The same system can also be used to mount prismatic reflectors. Forfixing suitable angle brackets are used. Two examples:

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Figure 121: Angle bracket for round prismatic reflector

Fixture of OJ There is no space for drill holes etc. for fixing on the housing of the verycompact new type OJ. Here type the housing has to be slid onto thefixture first.

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Figure 122: Fixture OJ

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Training manual

122

There are more accessories for this fixture, e.g. a ball joint which isknown in the field of photography.

Figure 123: Swivel-mount for OJ

4.4.3 Lens attachmentFor the cylindrical designs OF and OJ a minimum length has to be takeninto account. If the space is not sufficient a more compact design, e.g.OJ, or lens attachments may be used (available as accessories), whichdeflect the beam by 90°. Note that the range is reduced in this case andthat they are not suited for units with polarisation filters.

4.5 Overview

This section gives a short summary of the standard units. For the sake ofsimplicity the units with special properties will be presented in the nextsection.

Family It is typical of standard units that there are normally several variants ofone and the same design. This is called a family of units. The variants are:¡ through-beam sensors (T/B)¡ retro-reflective sensors (retro)¡ diffuse reflection sensors (diff)¡ diffuse reflection sensors with background suppression or for close

rangesTransmitters used:¡ LEDs (normally with infrared light)¡ laser diodesIn addition:¡ unit with lens¡ unit as amplifier for fibre opticsThere are also units which only operate with fibre optics.

Tables The following tables give an overview of the designs and families. Toensure a clear structure some information was summed up. To avoid anymisunderstanding the notes at the end of the tables should be observed.More details are given in the catalogue.


123

Designation Type T/B Ret. Dif. LED IR LED R Laser FibreOK rectangular

50*30*19

NOU rectangular51*16*28 P

OB

60*36*15P

VH

N

OC

42*49*15K

HOT

30*67*19P H

OL

62*75*27

PB

HOA

70*90*30

P

OD

80*53*30

C

OW

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60*10*36OJ

45*35*11

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Training manual

124

Designation Type T/B Ret. Dif. LED IR LED R Laser Fibre

BOF

M12P

POG

M18 H

OI

M30

Notes The stands for "existing" or "available". To keep the table clear it isnot shown which options exclude each other or can be combined. Itshould be possible to see this from the context. If there is for example a with Retro and Diff, there are two different units. If there is a with LEDIR and laser, there are also two different units. This means that bothRetro and Diff can be obtained with an IR LED or a laser as lighttransmitter. Fibre optic amplifiers are not operated with a laser diode.

Abbreviations Abbreviations are used for special properties.

P Unit with polarisation filter (for retro)C Colour sensor

for diffuse The following abbreviations are used for the different diffuse types:

H Background suppressionN Close rangeV Foreground suppressionK ContrastB Focussing

For special diffuse reflection sensors the light is focussed by means of aspecial lens. This enables detection of smaller objects or reduction ofenvironmental impact.


125

4.6 Units with special properties

4.6.1 Side or front lens

OJ A special characteristic of the OJ family is that virtually all units are availableboth with side and front lens. The very compact design is thus most effective.

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Figure 124: OJ with side or front lens

It was only possible to design such a compact type by leading the light tothe receiver via a reflector in the housing.

4.6.2 Separate amplifier

Amplifier (separate evaluation unit) Another possibility to detect objects located at places of difficult access inmachines or installations is to use opto efectors with separate amplifier.Transmitter and receiver are in a small housing with M8 thread orrectangular housing similar to the "microswitch". The electrical supplyand signal evaluation are made in an amplifier module. For these unitsthe specified cable length between transmitter/receiver and the separateamplifier (2m, 6m or 10m) must not be exceeded. Otherwise, this canlead to problems with the signal evaluation. The opto efectors type OEand OR with their amplifiers must always be seen as a complete system.One housing only incorporates the transmitting diode, the other thereceiving transistor. The signals are evaluated in the connected amplifier.

Figure 125: Design OE

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Training manual

126

The following mistakes are often made when these units are used:1. Wrong units are connected to the amplifier.2. The opto efectors are connected to wrong amplifiers.3. For reasons of cost the users try to build the amplifier themselves.4. Several transmitter and receiver units are connected to one amplifier.

T TransmitterR Receiver

Figure 126: Through-beam sensor with separate amplifier

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Figure 127: Block diagram OV 310

The OV 310 provides many other possibilities:


127

¡ Connection of 2 opto efectors, dark-on mode (D), light-on mode (H)and programmable (H*)

¡ Connection of inductive and capacitive 2 or 3-wire efectors¡ Blocking the output signal on terminal 8 of the amplifier, e.g. as start-

up delay for a machine¡ In the pulse mode the signal can be inverted. The unit then does not

switch on the rising edge but on the falling edge (and vice versa).¡ The output stage is a relay with a changeover contact. This results in a

switching frequency of max. 16 Hz.¡ The unit can be supplied with 24 V DC or 220 V AC.¡ The operating status is conveniently indicated by 3 LEDs:

power supply - greensignal of the opto efector � yellow (flashing) andoutput � red (LED is lit when the relay is energised)

To sum up it can be said that this unit almost is a kind of small controller.

4.6.3 Contrast sensor

The OC diffuse contrast sensor is specially sensitive to differences inintensity, i.e. contrast. It is specially suitable for detecting marks, forexample on a paper web. This is the only unit which is fitted with a greenLED (565 nm).

13.5 mm Note that the light spot is focussed at a distance of 13.5 mm.

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Figure 128: Contrast sensor

Inclination For highly reflecting objects a slight inclination of the unit isrecommended.

Adjustment Similar to the other units a potentiometer is used for adjustment andsetting.

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Training manual

128

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Figure 129: Setting of the contrast sensor

Proceed as follows:1. Set the potentiometer to the least sensitivity2. Place the lighter of the two materials within the sensing range (light3. spot must be on the object)4. Increase the sensitivity until the LED lights (= diffuse reflection sensor

is set to the lighter material)5. Place the darker of the two materials within the sensing range (light6. spot must be on the object)7. Increase the sensitivity until the LED lights (= diffuse reflection sensor

is set to the darker material)8. Set the sensitivity to a medium position between points 3 and 5 (the

unit receives light for the lighter material and no light for the darkermaterial)

4.6.4 Colour sensor

The basics of colour detection were discussed in 2.2.3. Here the practicaluse will be described. The applications are similar to those of the contrastsensor.

Figure 130: Colour sensor

Inclination For highly reflecting objects a slight inclination of the unit isrecommended again.

Transparent For transparent objects it must be checked whether the sensor can bemounted so that the light passes through the object. With a suitablereflector it then works as a retro-reflective sensor. For transparent objectsthis method is the preferred choice.

Setting The following Figure 131 shows the operating elements of the unit.


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Training manual

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131

5 Infrared sensors

Different Since these sensors operate to a principle which is different from thatdescribed above they are presented in a separate chapter.

Designation Occasionally these units are also called temperature sensors. This isslightly misleading.¡ The units are only conditionally suited for measuring a temperature

(see 5.1.2)¡ They should not be confused with the temperature sensors offered as

efector 600. These measure the temperature, display the values orprovide them as an analogue signal.

5.1 Operating principle

What for? Infrared sensors are intended for the non-contact detection of hot (oralso cold) objects. They are temperature-dependent electronic switches.They monitor and signal if a certain temperature is above or below a limitvalue. Like the efectors these units also provide a binary output signal.Analogue outputs are not available.

Some points which are detailed in 2.2 will only be briefly mentioned. Ifyou have problems in understanding, you should read this section again.

How? (brief explication) In principle, the efector 200 infrared sensors are photoreceivers whichreceive the heat radiation of the object to be detected and convert it intoa switching signal.The sensor function is based on the heating of a crystal by absorbinginfrared radiation. The resulting surface charge is indicative of theradiation capacity.

5.1.1 Radiation

No contact? Conventional sensing systems for temperature detection either needdirect contact with the object to be detected or at least a heatconducting medium (e.g. water, air) between object and sensor. Theinfrared sensors, however, detect the heat radiation emitted by theheated object which propagates as an electromagnetic wave in theinfrared range. This heat transmission by radiation needs no media suchas air or water, it is also possible in a vacuum. A good example of howthe radiation of the sun can be converted into energy is our Earth. Sincethe universe between sun and earth contains no heat conducting media,it receives the heat by electromagnetic radiation.

Passive sensors In principle, the efector 200 infrared sensors are photoreceivers whichreceive the heat radiation of the object to be detected and convert it intoa switching signal. As opposed to photoelectric sensors for example, theyreceive and convert no light from a specially arranged transmitter. Theheat radiation emitted by all bodies is received and evaluated.

Are they photoelectric sensors? The operating principle is optical, and so they can be assigned to thisproduct group. They can best be compared to diffuse reflection sensors

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which indicate: "object detected" or "object not detected" with the onlydifference that they emit no rays. To enable detection the object onlyneeds to emit a sufficient amount of heat radiation. But they can also beused similar to a photoelectric sensor. If they are set to a warmerbackground and the light beam is interrupted by a colder object, they canoperate as described above, only with the function being reversed. Thisway ice-cream can be detected on a conveyor belt using the type OWI.The user's and adviser's imagination is required to find such applications.

Heat radiation In section 2.1.2 the wave length ranges of electromagnetic radiationcovering infrared radiation are indicated. Infrared radiation can be seenas heat radiation. So the range is approx. 0.75 µm to 1 mm.

Wave length As can be seen in the example shown in Figure 14, there are receiverswhich have their maximum sensitivity in the infrared range. But for theinfrared sensors the whole width of the curve is not used. Due to suitablemeasures (filtering) the OWI receives wave lengths in the range of 6 to 14µm, the other types in the range of 0.9 to 2µm.

5.1.2 Degree of emission

For temperature detection with infrared sensors two factors play animportant role which influence the result. They are the degree ofemission and the wave length (see 2.2).

Radiation depends on the material Above absolute zero (0 K = -273 °C) all bodies emit electromagneticradiation. The intensity of this radiation depends on the degree ofemission "E" of the material and is an important criterion for theselection of the infrared sensor. The maximum radiation capacity has a"black emitter" (see 2.2.1 and Figure 11) with the degree of emission E =1. For setting the infrared sensors an emitter with E = 0.99 is used whichis very close to the ideal of the black emitter. The degree of emissionalways corresponds to its degree of absorption, i.e. the capacity to absorblight and other electromagnetic radiation or to reflect it. The followingpoints are very important for the practical applications of the infraredsensors:¡ The degree of emission E of the object to be detected should be as

high as possible.¡ The temperature of the object should be as high as possible (the

minimum temperature is the switching temperature of the sensor).¡ The radiation capacity should be as high as possible. It depends on the

volume and size of the surface of the object.


133

Some values for emission degrees are indicated in the attached table.Note the wide range of the values between 0.01 and 0.95!

Due to the different degrees of emission it is possible in practice that theswitching response of the infrared sensors is not the same for differentobjects despite the same surface temperature. Cast iron for example issafely detected but it is difficult to detect aluminium. This problem can besolved using a more sensitive sensor and a reduced range. Local tests arerecommended for materials which are difficult to detect (see 5.2). Thedegree of emission can also be improved by means of special lacquers(see 5.2.3).

Rule of thumb The darker, rougher and matter a surface is, the better the object isdetected. The lighter, smoother and more reflecting a surface is, themore difficult it is to detect the object although the temperature is thesame.

5.1.3 Technology

What is available? The product range covers sensors with fixed switching temperatures of350 °C, 500 °C, 750 °C and 900 °C and sensors with two separatelyadjustable switch points which can be set in the temperature range 50 °Cto 500 °C. The units with fixed switching temperatures are available withglass and fibre optics. Suitable accessories make mounting easy andenable a wide range of applications. The adjustable sensors are suppliedwith a plastic Fresnel lens.

For the time being no unit with fibre optic is available in the family withadjustable temperature range since glass absorbs the infrared radiation inthe wave range (solar heating). Glass fibre optics can only be used from atemperature above 350 °C.

The following diagram (Figure 133) shows the important data of thedifferent types. Calculation examples for the selection of a suitable sensorare given in 5.2.

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Figure 133: Overview of the infrared sensors

The electronics of the infrared sensors consist of a photoelement with apreamplifier, an evaluation and an output stage. The photoelement ofthe types OWS, OWL and OWF with a temperature range of 350 °C to500 °C consists of Germanium elements, silicon elements are used forthe range from 750 °C to 900 °C. The OWI has thermopile elements. Theinfrared radiation emitted by the object to be detected reaches thephotoelement through a lens. By absorbing this radiation the crystalheats up and results in a voltage change which is converted into aswitching signal by the evaluation and output stage. The switching statusof the respective output is indicated by a yellow LED. In addition, the OWItypes have a green LED to indicate the operating status.

Figure 134: Infrared sensor

The DC units are protected against short circuits, overload and reversepolarity. The voltage range is 10 - 55 V DC or 20 - 250 V AC/DC for theversions with a fixed switching temperature and 10 - 36 V DC for theunits with the two adjustable switch points. The electronics areincorporated into a robust, matt chromium-plated brass housing and arefully potted. The units feature the protection rating IP65. To reduceinterference by visible light all units are fitted with a powerful infraredfilter in front of the photoelement. The new OWI units have a Fresnel lenswhich is opaque to visible light (transparent range 6 - 14 µm).


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5.2 Information on practical use

One advantage of the non-contact temperature detection as comparedto other methods is that there is no mechanical connection between thesensor and the surface of the object, and thus the chemical compatibilitybetween sensor and medium is more or less no problem. Non-contacttemperature sensors detect temperature radiation as it is registered byour skin when a hot object is nearby.

5.2.1 Angle of aperture

Depending on the material temperature of the object to be detected thesuitable infrared sensor is selected. The maximum switching temperatureof the sensor should be as high as the object temperature. The choice ofa lower switching temperature increases the sensitivity. Furthermore, thesensitivity of the sensor directly depends on the selected range and theemission and absorption capacity of the object to be detected. Due to thebeam lobe the units have a circular sensing zone, the area of whichdepends on the range I and the respective angle of aperture of the unit(see drawing).

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Figure 135: Angle of aperture and range

What does this mean in practice? In practice, this results in questions such as: which unit (with which angleof aperture) must be selected when the object size (d) and distance (I) aregiven? Or: How long is the maximum distance (I) of the sensor when theobject size (d) and the minimum angle of aperture (0.6°) are given? Tohelp answer such questions the correlation must be examined. First theangle of aperture, then the formulas and calculation examples will bediscussed. Those who are afraid of having to calculate are referred to theFigure 136. If no solution is found, it may help to consider the degree ofcoverage (see farther below).

The angle of aperture is specified in the catalogue and on the type label.

Please note: This angle refers to the upper and lower limit of thedetection area (Figure 135). For the following geometric calculations itmakes more sense to use the angle against the horizontal line, i.e. /2. Inthis case the radius d/2 of the disc must be used instead of its diameter d.In a different context the angle /2 is referred to as angle of aperture.

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What is the angle of aperture? It is up to you to decide which angle ( or /2) is referred to as angle ofaperture. There is no need to lay this down in standards. For small anglesit is not necessary to be too precise. The result is more or less the samewhen /2 is replaced by and d/2 by d in the following formulas. This isso for all units except the special lens for fibre optics with 68°.

The following applies:

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Here are two examples:

1 A steel body of about 400 °C with a surface of about 50 cm² showing indirection of the sensor is to be detected at a distance of 4 m. The suitableinfrared sensor is looked for. The sensing zone area F must be no biggerthan the surface area of the steel body A, i.e.

F A = 50 cm²T = 400 °Cl = 4 m = 400 cm

From ( 10) you get:

cmcmd 98.7785.0

50 2

With ( 8) the angle of aperture of the unit is calculated.

pã 14.180098.7tanarc2cmcm


137

An infrared sensor with a switching temperature of 350 °C and an angleof aperture of 1° is selected. If the object to be detected is much biggerthan the calculated sensing zone, this results in a high excess gain (e.g. tocompensate for a dirty lens).

2 A steel body of about 850 °C with a surface of 0.5 m² showing indirection of the sensor is to be detected at a distance of 4.8 m. Aninfrared sensor with a switching temperature of 750 °C and an angle ofaperture of 1.2° is to be used, i.e.

A = 0.5 m ²a = 4.8 m

= 1.2 °

The diameter d of the sensing zone of the infrared sensor is calculatedaccording to ( 10):

d = 2 *4.8 m * tan 0.6° = 0.1 m

According to ( 9) the area of the sensing zone is as follows:

F 0.785 * (0.1 m)² = 0.00785 m² = 78.5 cm²

So the object surface is much bigger than the sensing zone of theinfrared sensor used. The object is therefore safely detected.

The following Figure 136 makes the selection of a suitable infrared sensoreasier. The sensing zone diameter, available angles of aperture andpossible ranges can be directly seen.

Thus the sensing zone of an infrared sensor with an angle of aperture of1° has a diameter of about 7 cm at a distance of 4 m. This means theobject to be detected with the respective surface temperature shouldfully cover at least an area with this diameter to ensure safe switching.

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Figure 136: Diagram angle of aperture - sensing distance � diameter

Degree of coverage If the degree of coverage is below 100%, the following measures mustbe taken to enable correct switching:- select another sensor with a lower switching temperature- reduce the range- increase the object temperature

The temperature response diagram below shows by how many degreesthe object temperature must be increased if the degree of coverage isless than 100%.

Figure 137: Degree of coverage and temperature

These values are only for guidance.


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5.2.2 Setting instructions for OWI

The units with a variable temperature setting have an angle of apertureof 7°. The following diagram represents the sensing area depending onthe range. For a reference emitter (E=0.99) the switch point can be set ina temperature range of +50 °C to +500 °C.

Figure 138: Distance and size for OWI

The factory setting of the sensors with a fixed temperature range ismaximum sensitivity and a defined temperature. This setting cannot bechanged from the outside. However, the OWI infrared sensors have twopotentiometers to set the reaction temperatures. It does not matterwhich output is used for the lower and which output for the upperreaction temperature.

Figure 139: Switching response of the OWI

Task The setting operation is to be explained by means of an applicationwhere a temperature window in a production system is to be monitored.It is not allowed to fall below a minimum temperature (130 °C) and toexceed a maximum temperature (150 °C).

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Output 1 is to switch at 130 °C.Output 2 is to switch at 150 °C.

Figure 139 demonstrates the switching response of the sensor dependingon the temperature.

The outputs 1 and 2 can be logically combined as follows:¡ No output: below the minimum temperature¡ Output A1: temperature in the requested range¡ Outputs A1 and A2: maximum temperature exceeded

Setting by means of the potentiometers is done as follows:

First, the potentiometers for output A1 and output A2 are turned tominimum sensitivity (anticlockwise stop).

The production system is now set so that the products with the lowertemperature limit pass the infrared sensor. The potentiometer for outputA1 is now turned clockwise until the output A1 switches. The sensor isnow set to the lower switching temperature. As soon as the output A1switches the minimum temperature is exceeded.

The production system is now set so that the products with the uppertemperature limit pass the infrared sensor. The potentiometer for outputA2 is now turned clockwise until the output A2 switches. The sensor isnow set to the upper switching temperature. As soon as the output A2switches, the maximum temperature is exceeded.

Constant degree of emission It has been tacitly assumed that the degree of emission remains constant.Apart from exceptional cases this is more or less correct.

5.2.3 Operating conditions

Temperature difference When setting the infrared sensor it must always be ensured that thetemperature difference between the object and the ambient temperatureis at least 20 °C.

Negative temperature difference A difficult application is described here. If the product to be detected iscolder than the environment, the worst case scenario is that the heatradiation of hotter adjacent bodies reflected by the object is monitoredand not the object temperature. This problem occurs in furnaces whereproducts are to be monitored for a maximum temperature.

Range The range for units with glass lens should not be above 5 m sinceotherwise radiation losses become too great. For fibre optic applicationswith attachment lens the range should not be longer than 1.5 m. Theinfrared unit is mounted at the requested position and aligned to theobject.


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Mounting For easy mounting a robust mounting base can be obtained as anaccessory.

High operating temperatures For operating temperatures above +60 °C a fibre optic must be usedwhich can withstand up to +250 °C. For the fibre optics attachmentlenses with an angle of aperture of 2° or 7° can be supplied asaccessories.

Background suppression Interfering background radiation can be suppressed by using a lesssensitive sensor with a higher switching temperature.

Lacquer A lacquer or foil coating is a solution for materials of a very low or veryirregular radiation. This results in a homogenised degree of emission of asurface. Lacquers for spraying which are listed in the following table arespecially suitable. These tried and tested coatings result in emission valuesof over 0.9. To ensure the requested success the lacquer coating musthave a minimum thickness which depends on the transmission properties.Note that this method does not detect the surface temperature of thematerial but the temperature of the lacquer coating. This can lead todifferences of a few degrees.

Lacquer for coating Thickness[µm]

E[µm]

Electrical insulatingprotective lacquer(solderable RL 659)

120 0.94 2...30

Electrical insulating coatinglacquer (RL 630)

100 0.92 2...30

Polyurethane lacquer(Syspur L 8632)

100 0.93 2...30

Matt cellulose nitratelacquer (black)

15 0.93 2...30

Black Krylon 12.5 0.98 5.6Parsons Black 50 0.96 5.6

Bright materials Another method to improve the detection of bright materials is anaccurate right angle (90°) installation of the infrared sensor referred tothe object to be detected.

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Hot steel sheets In rolling mills hot steel sheets are detected using infrared sensors.

Figure 140: Detection of hot steel sheets

The high temperature poses a problem when a sheet which is stillglowing passes the sensor very slowly. Dust trickling down can settle onthe lens. In winter the ambient temperature in rolling mills can almost bethe same as the temperature outside when big shutter doors are open.When the sheets move slowly they may cool down completely.

Protective tube To protect the units against dirt and lateral interference a protective tubecan be obtained as accessory. It is fitted with a compressed airconnection which can be used to automatically clean the lens (see Figure140).

Bright materials at low temperatures.Which conditions must be met?

To cool and protect the sensor against dust it must be blown with air. It isrecommended to incorporate the sensor into a protective housing of alow-radiation material (e.g. aluminium).

Typical applications for the OWI The higher requirements for quality assurance and increased productivityforce industry to increase automation. Whereas in the past the staffchecked the flow of materials the new sensor OWI is a low-cost system tomonitor production continuously and automatically.

The non-contact temperature detection is used for¡ moving parts¡ objects which are difficult to access¡ materials with low thermal capacities¡ live objects¡ adhesive materials such as dough, glue, etc.¡ objects with treated surface, e.g. lacquered¡ aggressive media such as acids and alkalis¡ applications where fast reaction times are required


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6 Applications

6.1 Photoelectric sensors

Strictly speaking, the infrared sensors also belong to this group. Sincetheir function and applications are different from those of the othersensors they are treated in a separate chapter (see 6.2) as was done withtheir technical features.

6.1.1 Recommended sensor types

Which sensor? Criteria to select inductive, capacitive, photoelectric sensors, etc. havebeen discussed in chapter 3.1. It is now assumed that you have decidedto use a photoelectric sensor.

Which type? You then still have to select the sensor type. In chapter 3 the differenttypes with their advantages and disadvantages as well as practicalinformation have been detailed. When it comes to solving specialapplication problems, you should consult this chapter. Below someselection criteria are summed up.

Through-beam sensor In general, one can say that a through-beam sensor should be usedwherever a high operational reliability is important. This type ofphotoelectric sensor enables a safe switching and a long range.

Retro-reflective sensor If it is not possible to use or mount a through-beam sensor or if thisinvolves too much work, a retro-reflective sensor could be taken intoaccount (safe switch point for most materials, half the range of that ofthe through-beam sensor, easier mounting, easy adjustment, etc.). If theretro-reflective sensor is to detect transparent objects, safe switching isachieved by setting the sensitivity of the receiver. For very shining objectssensors with polarisation filter should be used to increase immunity. Forvery small objects or restricted mounting space units with fibre optics orseparate amplifier can be used. Specially for small objects laser units arean excellent choice.

Diffuse reflection sensor The diffuse reflection sensor should be used when the object cannot bedetected with a through-beam or retro-reflective sensor, for examplewhen the object can only be detected from one side or when it is sotransparent that it cannot be detected using a through-beam or retro-reflective sensor. If there are problems with a diffuse reflection sensorcaused by reflection from the background, diffuse reflection sensors forshort ranges can be employed. As already mentioned, the sensitivity ofthe receiver can be set (reduced) with the potentiometer.

However, the sensitivity of photocells should only be set when almosttransparent objects are detected as this always reduces the operationalreliability. (For diffuse reflection sensors this setting is normally necessaryso that the diffuse reflection sensor safely detects the object and not thebackground). Due to programming, i.e. teach-in the optimum setting canbe easily found.

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Size The size of the objects also is a selection criterion. For very small objectsor little mounting space units with fibre optics or separate amplifiers arewell suited. Lasers are particularly suited for small objects.

6.1.2 Application examples

The following figures show a few examples of the numerous applicationsof photoelectric sensors.

Hot environment Fibre optics with metal sheath are suitable for temperatures up to 290°C. They are used for the detection of production goods with a highintrinsic temperature.

Figure 141: Hot environment


145

Edge monitoring For paper, plastic or textile webs through-beam and diffuse reflectionsensors are used for edge and sag monitoring.

Figure 142: Edge monitoring

Monitoring the filling operation The sensors check whether the cartons on a conveyor belt are filled.Empty cartons are rejected.

Figure 143: Monitoring the filling operation

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Monitoring a conveyor Photoelectric sensors detect objects at a larger distance, e.g. on aconveyor for metal plates.

Figure 144: Monitoring a conveyor

Storage technology Use of a retro-reflective sensor to monitor the height of a pile.

Figure 145: Retro-reflective sensor in storage technology


147

Anti-collision protection Photoelectric sensors are used as anti-collision detectors on a crane. Thebeam is oriented obliquely. Thus the beam only hits the prismaticreflector when the distance between the objects is too close. Doublingthe sensors results in double safety.

Note! The description of Figure 146 only concerns the safety of the machine.The user still has the duty to ensure that instructions which concern thesafety of people comply with the required approvals.

Figure 146: Anti-collision protection

Background suppression Diffuse reflection sensors with background suppression limit the sensingarea to adjustable geometrically limited areas. This enables the opticalsuppression of interfering elements (e.g. shining machine parts) whichare behind the product to be detected. Objects within the sensing areaare detected irrespective of their reflection properties (colour, size,surface). Thus the effective range does not depend on the product to bedetected but only on the set sensing area.

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Figure 147: Background suppression

Monitoring material on cutting machinesDiffuse reflection sensors type OI used to monitor material on anautomatic cutting machine. A fault is signalled in case of a tear.

Figure 148: Monitoring material on a cutting machine


149

Monitoring the supply of material Control of an automatic saw with a diffuse reflection sensor type OU. Itmonitors the material supply and controls activation of the drive.

Figure 149: Monitoring the material supply

Detection of contact lugs Photoelectric sensors with fibre optics are suitable for the detection ofminute parts due to their optical properties. They also detect quality-related details, e.g. contact lugs in the semiconductor production.

Figure 150: Detection of contact lugs

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6.2 Infrared sensors

Examples In chapter 5 the properties and operating conditions of the infraredsensors have already been described. Since there are only few infraredtypes and applications, it is not necessary to give a summary, someexamples are given straight away.

Infrared sensors are used where a non-contact safe detection of very hotand glowing parts is required. Such applications are mainly found inplants of the iron and steel industry, glass and ceramics industry,incineration plants, etc. Similar to other sensor types the infrared sensorsare used as temperature-dependent units for control and positioningtasks, for indicating limit values or as limit switches.Here is a list of applications for infrared sensors in different industries.

Blast furnaces¡ tapping control¡ discharge monitoring

Coking plants¡ control of quenching assemblies¡ monitoring of printing machines¡ monitoring conveyors for glowing hot spots¡ monitoring waste gas burners

Rolling mills¡ detection of slabs¡ control of roller tables¡ control of saws and shears¡ linear measurement¡ control of reversible operations¡ control of coiling equipment¡ control of slab washers

Foundries¡ control of foundry machines¡ monitoring tasks in the hot area¡ positioning tasks¡ tool protection by temperature monitoring

Glass and ceramics industry¡ monitoring tasks in the hot area

Incinerators¡ monitoring of burners¡ monitoring conveyors for glowing hot spots

Semiconductor production¡ sensing glowing wafers

More applications As a special application through-beam sensors can be set up for largedistances (approx. 50 m) using a halogen bulb as a transmitter and aninfrared sensor as a receiver.

Continuous casting machines Infrared sensors detect hot steel in continuous casting machines.


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Figure 151: Continuous casting machine

Length monitoring Infrared sensors monitor the length of hot steel pipes.

Figure 152: Length monitoring

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Slabs Infrared sensors are used to monitor slabs and hot rolled sheets in thesteel industry.

Figure 153: Slabs

Flames Infrared sensors monitor open flames of burners and waste gas burners.

Figure 154: Flames

Note This should be taken into account:¡ Some gas mixtures, e.g. blue flames from oxygen and hydrogen have

adverse radiation properties.


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Products from induction furnaces Detection of hot production goods from an induction furnace.

Figure 155: Goods from an induction furnace

Hot rolled wires Infrared sensors with fibre optics monitor hot rolled wires for break.

Figure 156: Hot rolled wires

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Glass bottles Infrared sensors count hot glass bottles in the hollow glass industry.

Figure 157: Glass bottles

Note This should be taken into account:¡ The cycle frequency can increase due to the various bottle sizes and

thus bottle diameters.¡ The distance between the bottles must be great enough.¡ The ambient temperature in the background should be much lower

than that of the objects.¡ The background should be free from reflections caused by interfering

heat sources.¡ For high frequencies or short distances the bottle neck should be

sensed.

Bulbs (1) For the manufacture of bulbs the screw bases are monitored for aminimum temperature of 300 °C.

Figure 158: Bulbs (1)


155

Note This should be taken into account:¡ Glass dust can soil the lens in the long term.¡ The operating temperature in the background should be much lower

than that of the objects.¡ The background should be free from reflections caused by interfering

heat sources.

Bulbs (2) The glass bulbs must be monitored for a temperature of 150 °C whenthey are covered with powder during the manufacture of matt glass.

Figure 159: Bulbs (2)

Note This should be taken into account: Glass dust can soil the lens in the long term.

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Jam bottling Temperature monitoring during food bottling is important because of thebest before date guarantee.

Figure 160: Jam bottling .

Note This should be taken into account:¡ Different compositions of food may lead to different radiation

intensities at identical temperatures due to different degrees ofemission. As a rule, such food has a high water contents. Since waterhas a high degree of emission, a change in the kind of jam to bebottled should have no considerable effects. A low water contentsmay pose problems.

¡ The infrared sensors should be protected during high-pressurecleaning. Mounting in a protective housing is thereforerecommended.

This application can be implemented for bottling various food, e.g. fruitjuices.


157

Soldering systems Infrared sensors are used to detect the position of PCBs in a solderingsystem.

Figure 161: Soldering system

Note This should be taken into account:¡ The temperature within the cover of the soldering system can exceed

100 °C. In this case the sensor must be cooled with gas blown intothe cover.

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Coating of profiled rails When profiled rails are coated with plastic infrared sensors are used fortemperature monitoring.

Figure 162: Coating of profiled rails

Edge banding For edge banding of wooden boards and pressboards in the furnitureindustry it is quickly monitored without contact whether glue is appliedto the edge. This is possible by using hot glue.

Figure 163: Edge banding


159

Appendix Type keysType key opto efectors

Pos. Designation Contents

1 Sensing principle O = optical2 Design 1 = distance sensor

2 = 2D sensor5 = rectangular housing 55,9 x 18,2 x 46,7A = rectangular housing 90 x 70 x 30B = rectangular housing 60 x 36 x 15C = rectangular housing 50 x 43 x 15D = rectangular housing 53 x 30 x 96E = cylindrical housing M8 x 1F = cylindrical housing M12 x 1G = cylindrical housing M18 x 1H = rectangular housing 25.1 x 7.6 x 12.5 I = cylindrical housing M30 x 1J = rectangular housing 24 x 36 x 11K = rectangular housing 50 x 30 x 18.5L = rectangular housing 62 x 75 x 27O = multiple fibre-optic amplifierP = rectangular housing 140 x 85 x 29R = rectangular housing 25 x 15 x 10S = rectangular housing 80 x 80 x 26T = rectangular housing 75 x 30 x 19U = rectangular housing 51 x 28 x 16V = opto amplifierW = rectangular housing 60 x 36 x 10 (for type W cylindrical infrared sensors please see separate type key for infrared sensors)X = special type

3 Function of the unit B = sensor with focussed light beamC = colour detectionD = 2D sensorE = through-beam sensor/receiverF = amplifier for fibre opticsG = U-shaped beam sensor (fork sensor)H = diffuse reflection sensor with background suppressionK = contrast sensorN = short-range diffuse reflection sensorP = retro-reflective sensor with polarisation filterR = retro-reflective sensorS = through-beam sensor/transmitterT = diffuse reflection sensorV = foreground suppression

4 Additional designation - = standardG = detection of glassI = infraredL = transmitted laser lightR = red lightX = special function

5 Switching function C = complementary outputD = dark-on mode (normally open function for through-beam and retro-reflective sensors, normally closed function for diffuse reflection sensors)F = light-on/dark-on mode programmableH = light-on mode (normally closed function for through-beam and retro-reflective sensors, normally open function for diffuse reflection sensorsM = switches if programmed colour detectedR = output switches when shape evaluation is readyV = for connection to amplifier (in which case positions 6 - 8 are not used)O = no output function (transmitter)

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Type key opto efectors

6 Output system B = semiconductor output for AC or AC/DC unitsC = semiconductor output PNP and NPNN = semiconductor output negative switchingP = semiconductor output positive switchingK = contact output (relay)O = no output function (transmitter)S = serial interface1 = analogue output 4 ... 20 mA2 = combined (analog 4-20 mA / binary)4 = analogue output 0 ... 10 V5 = combined (analog 0-10 V / binary)

7 Short-circuit protection K = with short-circuit protectionO = without short-circuit protection

8 Supply voltage A = either DC or AC voltageG = DC voltageW = AC voltage

9 Slash10 Options Bx = filter ( x = size; number of the filter)

D = DataMatrix codeFO = front opticGLx = connection for glass fibre optics (x = number of channels)GK = plastic housingGM = metal housingK = shape recognitionKLx = connection for plastic fibre optics (x = number of channels)RS232 = serial interface RS232RS485 = serial interface RS485SO = side opticT = time function

08.02.2005


161

Type key fibre optics

Pos. Designation Contents1 System fibre optics2 Mode of operation T = diffuse-type sensor

E = through-beam sensorU = universal

3 Reserve4-5 Amplifier to be connected 00 = OKF, OUF

11 = OBF18 = OGF30 = OIF50 = ODF, OMF, (OBF) X = special type

6 Reserve7 Sheathing A = aluminium-clad cable

E = polyetylene (PE)N = FPM (VITON)M = metal siliconeO = polyamide (PA)P = PVC sheathingS = siliconeV = V2A stainless steel (303S22)X = special type

8 Material fibre optics - = glassP = plasticX = special type

9 Material sensing head A = aluminiumM = nickel-plated brassV = V2A stainless steel (303S22)W = V4A stailnless steel (320S31)X = special type

10 Reserve11 Type of sensing head M = metric thread

E = smooth housingO = metric thread, 90° angledQ = rectangularR = smooth housing, 90° angledX = special type

12 Diameter of the sensing head in mm(for rectangular types smallest dimension)

13 "/"14 Options Fxxx = fibre-optic arrangement (number of fibres, core

diameter) e. g. F1 x 1; F16 x 0,25FH = semicircular fibre arrangement with separating lineFK = coaxial fibre arrangementFS = statistically mixed fibre arrangementFW = random fibre arrangementXm = total length in metres (not for standard fibres)

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Type key infrared heat sensors

Pos. Designation Contens

1 System O = Infrared heat sensor 2 Function W = heat

3 Type I = infra sensor (M30)L = long typeS = short type

4 Additional designation - = standard

5-6 Switching temperature 35 = 350 °C50 = 500 °C75 = 750 °C90 = 900 °C

7-8 Angle of aperture 00 = connection for fibre optics06 = 6°10 = 1°12 = 1,2°20 = 2°

9 Additional designation - = standard

10 Switching function A = normally open for two-wire units and for three-wire NPN units normally closed for three-wire PNP unitsB = normally closed for two-wire units and for three-wire NPN units normally open for three-wire PNP units

11 Output B = semiconductor output for AC and AC / DC unitsN = semiconductor output negative switchingP = semiconductor output positive switching

12 Short-circuit protection K = with short-circuit protectionO = without short-circuit protection

13 Supply voltage A = choice of AC or DC voltage (AC / DC)G = DC voltage

14 Slash15 Options

28.08.2003


163

d:\dokumente und einstellungen\dezeyegu\eigene dateien\lokalab05-04\materiallevele\originale\prodcode-e.docThis copy was printed on 03.06.04 enclosure to EA SIT-015

Explanation production code The coding is indicated on the type and box labels of our products or on an alternative type oflabelling, e.g. 'direct laser labelling' as it is used with the units in modular technology.

The coding covers information about Legend 'production site'

production site production month special designation

(meaning registered in the production site)

production status

E ifm ecomatic, KressbronnK ifm prover, Kressbronn (from 1/3/2000)P (bought-in products)S ifm syntronT ifm Tettnang (parent plant)U ifm USA (efector inc.)W ifm SwedenF ifm France

Current production code:

Standard coding Direct laser labelling(conventional units) (modular units)

Example: SA8 made byifm Syntron inOctober (A) 1998

- no special designation -

Example: 9903 made in 1999,in March (03)

AA first production status (AA)

T AB in the parent plantifm Tettnang ;second prod. status (AB)

- no special designation -

Old coding (until September 1995)

spec.des.

prod. site(see

legend)

prod.month(hex.)1...9,A,B,C

Prod. year(last pos.)

prod. statusAA...ZZ spec.

des.prod. site

(see legend)

prod. month(dec.) 01...12

prod. year(last two pos.)

prod. statusAA...ZZ

spec.des.

prod year(last pos.)

prod. month(dec.) 01...12

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164

Table degree of emission

The specifications in the table are only average values because the degreeof emission of a material is influenced by different factors such as: temperature sensing angle geometry of the surface (flat, concave, convex) thickness surface characteristics (polished, rough, oxidised, sandblasted, etc.)

Material E

Asbestos 0.95Asphalt 0,95Basalt 0.04Brick 0.93Carbon

not oxidisedgraphite

0.80...0.900.70...0.80

Carborundum 0.90China 0.92Clay (baked) 0.91...0.95Earth 0.90...0.98Fabric (cloth) 0.95Glass 0.85...0.94Gravel 0.95Gypsum 0.80...0.95Iron, galvanised 0.06Lacquers, enamel 0.93Limestone 0.98Paint (not alkaline) 0.90...0.95Paper (any colour) 0.95Plastics (transparent, 0.5 mm) 0.95Reference emitter 0.99Rubber 0.95Sand 0.90Water

snowice

0.930.900.98

Wood (natural) 0.90...0.95


165

Material E

Aluminiumnot oxidisedoxidised

Aluminium alloy A 3003oxidisedroughenedpolished

0.02...0.100.02...0.40

0.30.10...0.300.02...0.10

Brasspolishedhigh-polishedoxidised

0.01...0.050.300.50

Copperpolishedroughenedoxidised

0.030.05...0.100.40...0.80

Gold 0.01...0.10Haynes alloy 0.30...0.80Inconel

oxidisedsandblastedelectropolished

0.70...0.950.30...0.60

0.15Iron

oxidisednot oxidisedrustedskin

Iron, castoxidisednot oxidisedmoltenskin

0.50...0.900.05...0.200.50...0.70

0.770.60...0.95

0.200.20...0.30

0.80

Magnesium 0.02...0.10Mercury 0.05...0.15Molybdenum

oxidisednot oxidised

0.20...0.600.10

Monel (Ni-Cu) 0.10...0.14Platinum (black) 0.90Silver 0.02Steel

cold-rolledheavy platepolished sheetoxidisedstainless

0.70...0.900.40...0.60

0.100.70...0.900.10...0.80

Tin not oxidised 0.05Titanium

polishedoxidised

0.05...0.200.50...0.60

Tungsten polished 0.03...0.10Zinc

polishedoxidised

0.100.02


171

Glossary of technical terms

Absorption When a ray of light passes through a medium, radiation (or part of it) isconverted into another form of energy (e.g. heat) and is thus "lost". Thisprocess is called absorption.

Background suppression For applications with interfering high-contrast background behind theobject to be sensed diffuse reflection sensors with backgroundsuppression are used. These sensors operate to the focussed beamprinciple, the triangulation principle or the geometrical principle.

Current consumption in 3-wire units Current consumption is the internal consumption of the opto efector inits open condition.

Current rating/continuous This is the current at which an opto efector can be continuouslyoperated.

Current rating/peak This is the maximum current which can flow for a short time at themoment of switch on without damaging the opto efector.

Dark-on mode In the dark-on mode the receiver receives no light, the output is switchedand the load current flows through the load (IEC 60947-5-2). When thereceiver receives light, the load current is interrupted. For through-beamand retro-reflective sensors the dark-on mode corresponds to thenormally open function known from the inductive and capacitiveproximity switches (object present, output switched). For diffusereflection sensors the dark-on mode corresponds to the normally closedfunction.

Diffuse reflection sensor A diffuse-type sensor with transmitter and receiver located on the sameside of the plane to be sensed is called a diffuse reflection sensor (IEC60947-5-2).

Dispersion When a ray of light passes through a medium radiation or part of itundergoes a change in direction caused by collision with molecules. Thisprocess is called dispersion. Dispersion also takes place at boundarysurfaces if they are not flat in the area exposed to radiation.

Extraneous light interferon The function of photoelectric sensors can be affected by extraneous lightsources (in the visible and infrared spectrum). On data sheets of othermanufacturers the maximum permissible illuminance at which the safefunction of the unit remains ensured is sometimes denoted as extraneouslight interference and is specified in Lux. But this does not take intoaccount illuminance in the infrared spectrum which is at least of equalimportance!

Emission In general emission is the radiation of electromagnetic waves or minuteindivisible particles (corpuscles), e.g. light waves or electrons.

Illuminance The complete light flux which strikes a certain area is called illuminance.The unit of measurement is (lumen per square metre)1 Lux = 1 lm / m².

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Infrared Radiation with a wave length greater than that of visible light is calledinfrared radiation (IR), often also denoted as ultrared radiation. Threeranges are differentiated:

IR - A 780 nm to 1400 nmIR - B 1400 nm to 3000 nmIR - C 3000 nm to 25000 nm.

Law of reflection If a ray of light strikes the boundary surface of two media, radiation isreflected (totally or only partially) in accordance with the law of reflection("angle of incidence equals angle of reflection").

( 13) 1 = 2

Law of refraction If a ray of light passes from a transparent medium (e.g. air) into a moreopaque medium (e.g. glass), it is refracted to the optical axis inaccordance with the law of refraction

( 14) n1 sin 1 = n2 sin 2

with n1, n2 - refractive indices of the media1, 2 - angle of incidence, angle of reflection

The refractive indices depend on the material and the wave length.

Leakage current in 2-wire units Leakage current is the current which flows through 2-wire units in theopen condition to supply the electronics with current. The leakagecurrent also flows through the load.

Light Radiation in the electromagnetic spectrum which is visible to the humaneye is called light. This is the wave length range from 380 nm (violet) to780 nm (red).

Light-on mode In the light-on mode the receiver receives light, the output is switchedand the load current flows through the load (IEC 60947-5-2). When thebeam path is interrupted, the load current no longer flows. For diffusereflection sensors the light-on mode corresponds to the normally openfunction known from the inductive and capacitive proximity switches(object present, output switched). For through-beam and retro-reflectivesensors the light-on mode corresponds to the normally closed function.

Light barrier A light barrier is an arrangement of one (or several) transmitters whichsends a beam of light to one (or several) receivers. The change inillumination is converted into an electrical signal (IEC 60947-5-2).

Lux Unit of measurement for illuminance.Some examples:

20 to 40 Lux: street lighting at night250 to 500 Lux: normal office workover 1000 Lux: precision work done by handabout 2500 Lux : direct sunlight

Minimum load current The minimum load current is the smallest current which must flow in theswitched condition to supply the opto efector with current.


173

Operating temperature The operating temperature of the opto efector must be within the rangespecified in the data sheet. It must not exceed the maximum value or fallbelow the minimum value.

Operating voltage The nominal operating voltage is a value for which electrical equipment israted. For photoelectric sensors an operating voltage range is normallyspecified which defines the minimum and maximum value. The operationof the sensor is ensured within these limit values. Note that for DC unitsthe limit values include the residual ripple of the operating voltage. If theresidual ripple falls below the limit value of the operating voltage, asmoothing capacitor must be used.

Prismatic reflector A prismatic reflector is an optical component which retro-reflects incidentradiation (retro-reflection). Reflection is multiple and so almost withoutany loss. Radiation in the range of about ± 15° around the optical axis isretro-reflected with good efficiency.

Protection rating IP 61Complete protection against contact with live parts. Protection againstingress of dust.IP 65Complete protection against contact with live parts. Protection againstingress of dust and water jets.IP 67Complete protection against contact with live parts. Protection againstingress of dust. Protection against ingress of water when submerged to awater depth of 1 m for 30 min.

Radiation Radiation is a form of energy which can be described as anelectromagnetic wave, but also as a number of minute indivisible particles(photon, quantum). Depending on the wave length it is denoted as radiowave, heat radiation, light, X-radiation, etc. The unit of measurement forradiated energy is Ws (watt seconds). If only the visible spectrum ofradiation, i.e. light, is considered, the unit of measurement is lm s (lumenx seconds).

Range The mechanically useful distance between transmitter and receiver,transmitter-receiver and reflector as well as transmitter-receiver andobject to be sensed is called range (IEC 60947-5-2). For diffuse reflectionsensors the back of the Kodak Gray Card, 200 x 200 mm², is used as thereference object for measurements.

Reflection The reverberation of radiation at the boundary surface of two media iscalled reflection.The law of reflection applies.

Reflective foil A reflective foil is a low-cost optical component which retro-reflectsincident radiation (retro-reflection). Reflection takes place in smallspherical reflectors. Radiation in the area around the optical axis isreflected back with good efficiency.

Retro-reflection Retrodirection of a ray of light at a boundary surface is called retro-reflection. There are optical components (prismatic reflector, reflectivefoil) which retro-reflect incident radiation with good efficiency.

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Retro-reflective sensor A light barrier where the light of the transmitter-receiver is reflected by areflector located within the optical axis is called a retro-reflective sensor(IEC 60947-5-2). The optical means of the transmitter can also serve forreceiving the reflected light.

Switching temperature The switching temperature is the minimum temperature an object to besensed must have to enable switching of the infrared sensor. The visiblearea (sensing zone) of the infrared sensor must be completely covered.The switching temperature refers to a reference object ("black emitter").

Total reflection When passing from an opaque into a more transparent medium, the rayof light is refracted away from the optical axis in accordance with the lawof refraction. When the angle of incidence is 1 > b, with b = arc sin(n2/n1), no passing is possible but the light is totally reflected without anyloss. This critical angle is also called Brewster angle.

Transmission Passing of radiation through a medium is called transmission.

Through-beam sensor A light barrier where the transmitter sends light to a receiverincorporated into a separate housing is called a through-beam sensor(IEC 60947-5-2).

Ultrared See infrared.

Ultraviolet Radiation with a wave length shorter than that of visible light is calledultraviolet radiation (UV). Three ranges are differentiated:

UV - A 320 nm to 380 nmUV - B 280 nm to 320 nmUV - C 100 nm to 280 nm.

Voltage drop The voltage drop is measured across the switched opto efector at themaximum load current.


175

Index

1

13,5 mm................................................................127

4

4 stati ......................................................................88

6

6 pulses ...................................................................86

A

absorption .............................................................170AC ...........................................................................91active zone...............................................................47adjustable switch points .........................................133adjustment...............................................................36adjustment aid .........................................................47adjustment unit......................................................112ageing ...............................................................71, 83aggressive media......................................................67aluminium extrusion...............................................114ambient temperature .............................................140amplifier ..........................................................68, 125analog .............................................................85, 108analyser ...................................................................49angle bracket .........................................112, 116, 117angle of aperture .............................35, 135, 136, 139anti-collision protection..........................................147application examples..............................................144applications....................................................142, 143approximate calculation .........................................136area .......................................................................136AS-Interface .............................................................89attenuation ........................................................31, 68automatic ....................................................59, 80, 97avalanche.................................................................25

B

background ...............................................58, 79, 100background suppression ..................60, 102, 147, 170basic level ................................................................16bend ........................................................................73bending cycles .........................................................69bending radius .........................................................73binary sensors ..........................................................32black ........................................................................23black emitter..............................................21, 22, 132block diagram ..........................................................83Bohr atom................................................................15bulbs..............................................................154, 155burners ..................................................................150buttons ....................................................................60

C

cable length ...........................................................125cap...........................................................................39Caution....................................................................94ceramics industry ...................................................150changeover contacts ................................................96characteristics ..............................................35, 47, 55characteristics of diffuse reflection sensors ...............58characteristics of the retro-reflective sensor........47, 53characteristics of the through-beam sensors.............42chemicals .................................................................71clamp.............................................................112, 117class .........................................................................26close range ..............................................................37coherent ......................................................17, 25, 26coiling equipment ..................................................150colour ................................................................22, 57colour filter ..............................................................23colour sensor .......................................23, 24, 66, 128compact...................................................................67connection...............................................................92contact lugs ...........................................................149continuous casting machines..................................151contrast....................................................................23contrast sensor.................................................65, 127conveyor ................................................................146counting bottles.......................................................53coupling...................................................................69crank......................................................................116cube.......................................................................114current consumption........................................92, 170current rating/continuous.......................................170current rating/peak ................................................170cut plastic fibre to size..............................................72cycle frequency ........................................................83cycle generator ........................................................83

D

danger .....................................................................11dark-on mode ........................................................170dark-on switching ....................................................73DC .....................................................................91, 96dead zone..........................................................51, 61decentralisisation ...................................................106degree of coverage ................................................138degree of emission...................................22, 132, 164diameter ................................................................136diameter of the light spot.........................................28diffraction ................................................................14diffuse reflection sensor .....................54, 85, 143, 170diffuse reflection sensor as retro-reflective ...............66diffuse reflection sensors for short ranges ................60

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digital.......................................................................85digital noise suppression...........................................86DIN 5031 .................................................................13directional ................................................................25discharge monitoring ............................................ 150dispersion........................................................ 11, 170display................................................................... 102distance .......................................................... 36, 135duality ......................................................................10dust..........................................................................15dynamic .................................................... 59, 80, 101

E

edge banding........................................................ 158edge monitoring ................................................... 145electromagnetic radiation spectrum .........................13electromagnetic waves .............................................11elektronically ............................................................60emission.......................................................... 17, 170EN 60825.................................................................26energy......................................................... 11, 16, 26energy level ..............................................................16excess gain.............................. 36, 39, 58, 63, 76, 104excess gain curve......................................................77excess gain factor.....................................................79excitation .................................................................16exposure ..................................................................57extraneous light .......................................... 21, 40, 64extraneous light interferon .................................... 170eyelid closing reflex ..................................................26

F

failure warning.........................................................88family .................................................................... 122FAQ............................................................................8far range ..................................................................37fc .............................................................................95fibre .................................................................. 30, 31fibre optic ................................................................68fibre optic amplifier ..................................................97fibre optics ........................................................ 67, 68filling operation..................................................... 145fine adjustment ..................................................... 118fixed switching temperatures ................................ 133fixtures ............................................................ 69, 112flames ................................................................... 152focus ................................................................. 28, 65focussed beam principle ...........................................62focussed light beam .................................................65focussing..................................................................28foreground suppression............................................65foundry machines.................................................. 150frequency.................................................................11frequency filter.........................................................85function check output ....................................... 88, 95funktion display........................................................87further support...................................................... 106

G

GaAlAsP .................................................................. 19GaAs ....................................................................... 19GaAsP ..................................................................... 19gate circuit .............................................................. 85geometrical optics ................................................... 14glass........................................................................ 69glass bottles .......................................................... 154glass fibre................................................................ 71glossary ................................................................. 170glowing hot spots ................................................. 150granular .................................................................. 26gray card ................................................................. 57green .............................................................. 66, 127guarantee.................................................................. 2

H

handling.................................................................. 97heat radiation................................................ 131, 132high operating temperatures ................................. 141high temperatures............................................. 67, 71highly reflective foils................................................ 50high-pass filter ........................................................ 85hot area ................................................................ 150hot environment ................................................... 144hot rolled wires ..................................................... 153hot steel sheets ..................................................... 142hysteresis................................................................. 55

I

IEC 60825 ............................................................... 26illuminance............................................................ 170image-creating ........................................................ 32immunity to interference ......................................... 33Incinerators ........................................................... 150inclination ............................................................. 127incoherent................................................... 17, 18, 25induction furnaces................................................. 153infrared ..................................................... 12, 13, 171infrared sensor ........................................ 21, 134, 136infrared sensors ..................................................... 131initial state............................................................. 104intensity .................................................................. 11interference..................................... 10, 13, 14, 26, 58interfering background pulses ................................. 88interpretation .......................................................... 10IR light..................................................................... 12

J

jam bottling........................................................... 156

K

Kodak gray card ...................................................... 57


177

L

lacquer...................................................................141laser ...................................... 24, 25, 34, 37, 104, 112laser and prismatic reflector .....................................50laser diod .................................................................20laser diode ...............................................................25laser protection class ................................................26laser sensors...........................................................118latching..................................................................104law of reflection.....................................................171law of refraction ....................................................171leakage current ................................................92, 171LED ..................................................................19, 105length measurement ................................................32length monitoring ............................................32, 151light ............................................. 10, 171 see velocitylight barrier ............................................................171light spot .........................................................36, 127light-on mode ........................................................171light-on switching ....................................................73linear measurement ...............................................150load current .............................................................92longevity ..................................................................83Lux.........................................................................171

M

manual ....................................................................59marks.......................................................................65mecanical strain .......................................................71mecanically ..............................................................60metal silicone ...........................................................71metal-clad sheathing................................................71microprocessor.........................................................60minimum load current............................................171mistakes.................................................................126monitoring material .......................................148, 149monochrome ...................................18, 19, 20, 24, 25mounting.........................................................36, 105mounting set .........................................................112movement ...............................................................72moving objects.........................................................99mutual interference..................................................38

N

negative temperature difference ............................140noise suppression...............................................83, 84non-contact temperature .......................................142non-contact temperature detection........................135non-directional.........................................................18non-drectional .........................................................24normally closed/open ...............................................74

O

OA.................................................................105, 110OAH.......................................................................111OB .........................................................................108

object.......................................................................79object size ..............................................................135OC.........................................................................127OCK.........................................................................65OCNL .......................................................................65OCPG.......................................................................53OCV.........................................................................65ODC.........................................................................66OE..........................................................................125OFB..........................................................................65OG...........................................................97, 112, 117OGTL .......................................................................65OKF..........................................................................68OL..................................................................112, 119on or off delay .......................................................107operating temperature ...........................................172operating voltage...................................................172optical......................................................................60optimum setting ................................................58, 78optimum switch point ..............................................80OR .........................................................................125order......................................................................101OS..........................................................................107OV 310 ..........................................................107, 126OWI .......................................................................139

P

parallel mounting.....................................................38particle.....................................................................10partly transparent.....................................................98passive sensors.......................................................131photoelectric............................................................32photoelectric sensor .................................................32pinch........................................................................73plastic ......................................................................69plastic fibres .................................................31, 71, 72polarisation ..............................................................12polarisation filter ......................................................48polariser ...................................................................48population inversion.................................................27positioning .............................................................150potentiometer ....................................................59, 78power supply .....................................................91, 92precise alignment...................................................112printing machines ..................................................150prismatic reflector ..........................................120, 172prismatic reflectors for lasers ....................................50processor ...............................................................108profiled rails ...........................................................158protection class ........................................................26protection rating ....................................................172protective shroud ...........................................112, 120protective tube.......................................................142PSD..........................................................................63pumping ..................................................................27PVC..........................................................................71

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Training manual

178

Q

quality of a prismatic reflector ..................................51quantum ..................................................................15quenching assemblies............................................ 150

R

radiation ............................................................... 172range .......... 34, 47, 51, 56, 63, 64, 65, 136, 140, 172ratio on/off...............................................................83R-C combination ......................................................92receiver ............................................................. 35, 94receiver transistor .....................................................13recommended sensor types................................... 143red light ............................................................ 15, 68reflection......................................................... 22, 172reflective foil ............................................. 45, 49, 172reflective objects ............................................... 39, 48reflective quality .......................................................55reflective surface ......................................................41reflector ...................................................................25refraction .................................................................29refraction index ........................................................30relay output .............................................................96reliable .....................................................................67relliability..................................................................50resistant to ageing....................................................71resistor .....................................................................92resonator .................................................................25retro-reflection ...................................................... 172retro-reflective sensor........................ 43, 84, 143, 173RGB..........................................................................23rod ........................................................................ 113roller tables ........................................................... 150ruby laser .................................................................27rule of thumb........................................................ 133

S

saws...................................................................... 150science of colours.....................................................23screen ......................................................................39selection................................................................ 137sensing head ............................................................69sensing range41, 57, 62, 76 see also range see rangesensing zone ......................................................... 137sensitivity .................................................................20sensor types .......................................................... 143setting................................................................... 106setting......................................................................78setting aid ............................................................. 104setting of the sensing range ............................ 97, 100shears.................................................................... 150sheathing .................................................................67simple installation.....................................................53size...........................................................................34size of the prismatic reflector ...................................47slab washers.......................................................... 150

slabs.............................................................. 150, 152slot........................................................................ 114small objects................................................ 28, 65, 67socket ..................................................................... 94soiling ............................................................... 14, 88solar radiation ......................................................... 19soldering systems .................................................. 157spacers .................................................................... 41spectral curves......................................................... 20spectral distribution................................................. 18spectrum..................................................... 12, 18, 19spontaneous emission ............................................. 17squeeze................................................................... 73static ..................................................................... 100stimulated emission................................................. 25Strahlungsspektrum ................................................ 18surface .................................................................. 113surface characteristics.............................................. 55switching temperature .......................................... 173system................................................................... 112

T

tapping control ..................................................... 150teach In ................................................................... 97teaching .................................................................. 97technical terms...................................................... 170temperature difference.......................................... 140tensile strain ............................................................ 73terminal chamber .................................................... 93test.......................................................................... 93test input........................................................... 89, 93three-dimensional angles....................................... 112through-beam sensor ........................ 83, 93, 143, 173tighten .................................................................... 73timer ..................................................................... 109timers.................................................................... 106tool protection ...................................................... 150total reflection......................................................... 30Totalreflexion ........................................................ 173transmitter .............................................................. 35transverse................................................................ 11triangulation principle ............................................. 63TS80........................................................................ 47twist........................................................................ 73typical ..................................................................... 46typical graph ........................................................... 46

U

UC .......................................................................... 96ultrared ................................................................. 173ultraviolet ........................................................ 12, 173universal................................................................ 112universal current...................................................... 91UV light................................................................... 12


179

V

velocity of light ..................................................11, 29versatile ...................................................................67voltage drop ....................................................92, 173

W

wafers....................................................................150waste gas burners ..................................................150

wave ........................................................................10wave length .................................. 11, 12, 13, 14, 132wear and tear ..........................................................83wet areas .................................................................71white .......................................................................23wiring diagram.........................................................97

Z

zoom .......................................................................28

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