infrared thermographic system

7/30/2019 Infrared thermographic system

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INFRARED THERMOGRAPHIC SYSTEMS AND THEIR

MECHANICAL APPLICATIONS.


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ABSTRACT

Infrared thermography is the science of detecting and measuring variations in heat emitted by an

object and transforming them into visible images. Infrared Thermal Imaging is an electronic

technique which quite literally allows us to see thermal radiations. With this new capability,

plant maintenance personnel have recognized Infrared Thermal Imaging as one of the most

versatile and effective condition monitoring tools available today. Infrared thermography can

detect numerous conditions in which an anomaly is characterized by an increase or decrease in

surface temperature or retained residual heat. These include high resistance heating of

connection points in electrical systems; heat generated by abnormal friction in bearing surfaces;


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differences in heat transfer across surfaces, such as a wall or boiler; and moisture retained in

insulation in a roofing system. Infrared imaging, when combined with software analysis tools,

may also be used to quantify these types of thermal differences.

Infrared Thermal Imaging is an excellent condition monitoring tool to assist in the reduction of

maintenance costs on mechanical equipment. The technique allows for the monitoring of

temperatures and thermal patterns while the equipment is online and running under full load.

Most mechanical equipment has allowable operating temperature limits that can be used as

guidelines. Unlike many other test methods, Infrared Thermal Imaging can be used on a wide

variety of equipment including pumps, motors, bearings, pulleys, fans, drives, conveyors etc.

Advantage of these methods is contactless measurement, usually very fast and without any

destructive influence on tested/measured objects

CONTENTS

List if figures..5 Notations....6


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Introduction..7 History..8 Theory..9 Common infrared thermometer construction.13 Surface temperature in infrared thermometers...14 Elements in infrared thermometer..15 Temperature measurement calculations.19 Types of infrared thermometers.22 Advantages and disadvantages of IR thermometry....25 Non-destructive evaluation.26 Application.29 Conclusion..40 Future of IR imaging...41 References...42

LIST OF FIGURES

Fig 3.1: Splitting of incident energy.10

Fig3.2: Spectral Distribution....11


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Fig 4.1: Optical arrangement in IR detector......13

Fig 4.2: Block diagram of IR thermographer.13

Fig 5.1: Hemispherical IR thermometer15

Fig 6.1: Field of view..17

Fig 10.1: Fast transient NDE27

Fig 10.2: Steady state NDE.....28

Fig 11.1: Thermographs for comparing working of motors30

Fig 11.2: Thermograph of belt and pulley.30

Fig 11.3: Thermograph of a faulted bearing......31

Fig 11.4: Thermograph of a steam trap.32

Fig 11.5: Thermograph of a defective steam trap...33

Fig 11.6: Thermograph of a rotary kiln.....34

Fig 11.7: Thermograph of a blower system...35

NOTATIONS

WI = incident energy received by the object, W

WR = energy reflected off the objects surface, W

WT = energy transmitted by the object, W

WA = energy absorbed by the object, W


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E = emissivity

= Stefan-Boltzmann Constant = 5.6703 10-8

, W/m2K

4

T = absolute temperature,oK

A = emitting area, m2

TIR = Surface temperature,K

esurf = Emissivity of the surface

Tback = Background Temperature,K

TIR, Ref = Emitter temperature.K

TIR, smpl = sample surface temperature,K

TFOV = The uncertainty in temperature due to variations in field of view,K

TLin = The uncertainty in temperature due to non-linear performance of the

imager.K

T = The total uncertainty in the measured surface temperature,K

1.0 INTRODUCTION

Temperature is one of the important parameters to tell the condition of internal process, material

and even quality of the desired output. A qualitative but accurate conclusion can be drawn by

observing the temperature profile of any surface. On the other hand higher temperature also

indicates obvious loss of energy in the form of heat. Therefore temperature monitoring would

give ample indication of the condition of the material, process quality and explore the possibility

of energy conservation avenues. In recent years, many temperature monitoring techniques have

been in use in our industries. These techniques find their application based on the measurable

temperature range, sensitivity and ease in application. With the on-line condition monitoring


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technology becoming an inevitable part of maintenance strategy in todays scenario, non -contact

type temperature monitoring methods have become more popular. Infrared Thermography is

such a non-contact type technique which provides a fast, reliable and accurate temperature

profile of any material surface. This paper deals with various application of infrared

thermography including the justification of energy saving potential in many cases.

Infrared (IR) energy is part of the electromagnetic spectrum and behaves similarly to visible

light. It travels through space at the speed of light and can be reflected, refracted, absorbed, and

emitted. The wavelength of IR energy is about an order of magnitude longer than visible light,

between 0.7 and 1000 m. All objects emit infrared radiation as a function of their temperature.

Infrared energy is generated by the vibration and rotation of atoms and molecules. The higher the

temperature of an object, the more the motion and hence the more infrared energy is emitted.

This is the energy detected by infrared cameras. The cameras do not see temperatures, they

detect thermal radiation. At absolute zero (273.16C, 459.67F), material is at its lowest

energy state so infrared radiation is minimized.

Infrared thermography is the technique for producing an image of invisible (to our eyes) infrared

light emitted by objects due to their thermal condition. An image produced by an infrared camera

is called a thermogram or a thermograph. Infrared (IR) thermographic systems, or IR imagers,

provide images that represent surface temperatures, by measuring the magnitude of infrared

radiation emanating from the surface of an object. Because IR imagers see the radiation naturally

emitted by objects, imaging may be performed in the absence of any additional light source.

Modern IR imagers resolve surface temperature differences of 0.1C or less. With this high

sensitivity, they can evaluate subtle thermal phenomena, which are only revealed in the form of

slight temperature gradients. Some applications that employ IR thermography include:

inspections for predictive maintenance, non-destructive evaluation of thermal and mechanical

properties, building science, military reconnaissance and weapons guidance, and medical

imaging.


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2.0 HISTORY

The first patent for a total radiation thermometer was granted in 1901. The instrument used a

thermoelectric sensor; it had an electrical output signal and was capable of unattended operation.In 1931, the first commercially-available total radiation thermometers were introduced. These

devices were widely used throughout industry to record and control industrial processes. They

are still used today, but mainly used for low temperature applications. The past 20 years, non-

contact infrared thermometer in the rapid development of technology, performance, continuous

improvement, function continuously enhanced, increasing variety, scope also expanded its

market share year by year.

3.0 THEORETICAL BASIS FOR RADIATION

MEASUREMENTS

Heat is transferred from one body to another through conduction, convection, or radiation.

Radiation is a process where heat energy in a form of electromagnetic waves is emitted by a hot

object and absorbed by a colder object. Most of this radiation is in the infrared (IR) region of the

electromagnetic spectrum, but some also spreads into the visible light band. The IR wavelength

band stretches from 0.7 to 1000 microns, however practical IR measurement systems use only


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certain wavelength bands between 0.7 and 14 microns because the radiation is the strongest in

this range.

If an object is exposed to IR energy radiated by a heat source, such as an electric heater, light

bulb, sun, or other source, the energy reaching the object is called incident energy. Part of this

energy is reflected off the object surface. Theoretically, the objects coefficient of reflectivity can

vary from 0 (no reflection) to 1.0 (100% reflection). Rough, matt surfaces have low reflectivity.

Polished and glossy surfaces, especially metals, have high reflectivity.

Depending on the object material, thickness, and the radiation wavelength, part of the radiation

can go through the object or be transmitted. The coefficient of transmission can vary from 0 (no

energy transmitted through object) to 1.0 (100% energy transmitted through object). High

transmittance examples include glass, quartz, plastic film, and various gasses. Materials opaque

in the IR spectrum have close to zero transmission coefficients.

The remaining energy is absorbed by the object and raises its temperature. A hypothetical body

that has no reflection or transmission and absorbs all incident energy across the entire spectrum

has a coefficient of absorption equal to 1.0 and is called a blackbody. Real-life objects, referred

to as gray bodies, have coefficients of absorption that fall between 0 and 1.0.

Incident energy, WI, is defined as:

WI = WR+ WT + WA

Fig 3.1Splitting of incident energy


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When incident heat energy reaches an object, part of this energy is reflected, part passes through

the object, and the rest is absorbed. The coefficients of reflection, transmission, and absorption

depend on the object material and surface finish and on the wavelength spectrum of the incident

energy.

As the object absorbs energy and heats, it also emits energy. When an object is in a state of

thermal equilibrium, the amount of energy it absorbs (WA) equals the amount of energy it emits

(WE): WA = WE. When an object absorbs more energy and its temperature increases, the amount

of radiation it emits also increases.

IR thermometry is based on the fact that any body (solid, liquid, or gaseous) that has a

temperature above absolute zero (0oK or -273

oC) emits radiant energy. This energy is

proportional to the forth power of the body temperature, and the bodys ability to absorb and

emit IR energy is called emissivity. Energy radiated by a body can be expressed as follows:

W = E A watts.

Fig 3.2 Graph showing relation between wavelength and temperature


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When the temperature of a hypothetical blackbody increases, the radiated IR energy also

increases. Temperature T2 is several times greater than temperature T1. The rise between 1 and

10 microns is most pronounced.

Emissivity can range from 0 to 1 for various bodies. A hypothetical blackbody emits and absorbs

all energy and thus has an emissivity equal to 1. Real-life objects have an emissivity between 0

and 1.

When an IR thermometer measures an objects temperature, consider the energy that actually

enters the lens. That is, in addition to emitting energy related to its own temperature, the object

may reflect energy coming from another source, or transmit energy passing through it from a

source behind it. Thermal radiation is largely a surface phenomenon, because most materials arenot transparent to IR. As a result, it is the material properties of the surface of an object that

determine emittance. Polished metals have low emittance, but a thin layer of paint can transform

them to high emittance. For materials that are opaque to IR radiation, emittance can be

considered the complement of reflectance (the amount of incident radiation that is reflected by a

surface), expressed by 1-e. It is important to realize that because no real surface has an emittance

e=1, the radiation that is viewed as coming from an object is always a combination of emitted

and reflected radiation, termed radiosity, and it contains information regarding both the

temperature of the object and its surroundings. Special techniques described within are necessary

to distinguish the two components and obtain accurate surface temperatures for the object of

interest. When imaging outdoors, it should be taken into account that the sun is a significant

source of IR radiation, particularly in the shorter wavelengths of the IR band.

For accurate measurements, survey the surrounding area for possible sources of extraneous IR

radiation and choose the thermometer position and aiming angle to minimize the effects of those

sources


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4.0 COMMON INFRARED THERMOMETER CONSTRUCTION

The most basic design consists of a lens to focus the infrared thermal radiation on to a detector,

which converts the radiant power to an electrical signal that can be displayed in units of

temperature after being compensated for ambient temperature.


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Fig 4.1 Optical Arrangement

Fig 4.2 IR imager flow diagram

This configuration facilitates temperature measurement from a distance without contact with the

object to be measured. As such, the infrared thermometer is useful for measuring temperature

under circumstances where thermocouples or other probe type sensors cannot be used or do not

produce accurate data for a variety of reasons.


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The majority of IR detectors are either single-wavelength (also called single-color), or dual-

wavelength (also called two-color) type. The single-wavelength detectors measure IR energy

within a certain wavelength band, and the instrument calculates object temperature based on the

detector output and the preset emissivity. Some thermometers have adjustable emissivity, and

most simple units have fixed emissivity.

Dual-wavelength detectors measure energy at two different wavelength bands, and the

instrument calculates temperature based on the ratio of the two readings. If emissivity or the

energy changes by the same amount at both bands, the measurement accuracy is not affected.

Emissivity or the amount of radiated energy may change due to object change or movement, lens

contamination or misalignment, or view obstruction. The dual-wavelength detectors drawback

is higher cost and lower accuracy under certain conditions

5.0 SURFACE TEMPERATURE INFRARED THERMOMETERS

We have seen that a radiation source with characteristics close to that of a blackbody could beconstructed by assuring multiple reflections within a cavity. Fig. 8 illustrates a device for

measuring the temperature of the surface of an object based on this principle

Fig 5.1 Surface temperature infrared thermometer


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Radiation from the target is multiply reflected from the hemispherical mirror. A detector receives

radiation through a small opening in the reflector. The radiation multiply reflected between the

mirror and the target appears to the detector to be from a blackbody. A commercial thermometer

using this principle can read the temperature of targets with emittance as low as 0.6 without

correction. The reflector must be placed close to the surface being measured to exclude

extraneous radiation and prevent radiation losses.

6.0ELEMENTS OF INFRARED THERMOMETERS

6.1 DETECTORS

Based on the principle of operation, IR detectors fall into one of two categories: thermal

detectors and photo detectors (photodiodes). Thermal IR detectors absorb the incident energy,

raise the sensing element temperature, and change the detectors electrical properties:

thermopiles generate thermoelectric voltage, bolometers change resistance, and pyroelectric

devices change their polarization. In general, they are slower than photo detectors.

A thermopile is made by connecting several thermocouples in series and placing their hot

junctions in contact with a black body that absorbs the incident IR energy and heats the hot

junctions. The cold junctions are placed in the area of the detector with adequate heat sinking.

These detectors have fast response, broad band, large dynamic range, and are frequently used in

general-purpose, automotive, air conditioning, and human-body thermometers.

Bolometers use a slab of material that changes its resistance in response to a change of

temperature. The circuit converts resistance change to a voltage change, which is further

processed by the instrument. Bolometers are frequently used for measuring low-level IR energy,

often as an attachment to a telescope.

Pyroelectric devices become electrically charged when their body temperature changes. To

produce a usable signal, the incident IR energy has to pulse. The output peak-to-peak AC

signal is proportional to the pulse energy. Since energy emitted by measured objects is usually

steady, thermometers that use pyroelectric detectors have a mechanical or optical chopper in

front of the sensor. These sensors are used in many home security systems.


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Photo detectors are built on a silicon substrate with an IR sensitive area that releases free

electrons when impacted by the photons. The flow of electrons produces electrical signals

proportional to the incident energy. These detectors are often used as arrays in thermal imaging

systems.

A detector needs protection from the environment, and the selected window material must allow

the correct wavelength band to pass through with minimum attenuation. A zinc sulfide or

germanium window is best for the long-wavelength detectors, glass is suitable for short-

wavelength detectors, and quartz for the mid-wavelength spectrum. Some instruments use a

fiber-optic light guide to direct the radiation to the detector.

6.2 OPTICAL SYSTEMS

The optical system of an IRT may be composed of lenses or mirrors or combinations of both.

Mirror systems have been common mainly in fixed focus optical systems. To vary the focus of

an optical system requires that at least one element be movable. Providing for this motion in

mirror systems is often more complicated than in lens systems. The selection of lens and window

materials is always a compromise between the optical and physical properties of the material and

the desired wavelength response of the pyrometer.

6.3 DATA ACQUISITION AND IMAGE PROCESSING

Collecting image data is an important part of operating a real-time imager. The data are

commonly recorded for later analysis, assembly into reports, etc. Continuous video signals may

be recorded on tape or with the aid of a computerized video digitizer. In steady-state thermal

situations a single IR image would be generated by averaging a number of frames over a period

of time. Transient thermal situations are usually recorded continually, and a series of images are

stored over time.


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6.4 FIELD OF VIEW

Fig 6.1 Field of view

The key specifications and considerations for any IR thermometer application are field of view

(FOV) and distance; spectral band; response time; accuracy and repeatability; emissivity of the

object or media being measured; media between the object and IR thermometer, such as vacuum,

air, steam, gas, glass, or other; object temperature range; mounted or hand-held application; and

type of output signal or display.

The FOV characterizes the diameter of a circle (target) that the IR detector will see at a certain

distance from the measured surface. However, there is always a minimum target diameter that

depends on the optical system and detector size. The detector measures and averages

temperatures of all objects within the target area. FOV is commonly called distance-to-spot size

ratio and is a ratio of the distance between the meter and the target to the diameter of the

target.For example, a 10:1 distance-to-spot size ratio means that if a measured surface is located

10 inches from the thermometer it will measure and average the temperature of a circle with 1

in.diameter. Move the thermometer away to 20 in. and the target will increase to 2 in., and so on.

A thermometer with a 1:1 ratio will measure within a one-foot diameter circle when held onefoot away from the target.Thermometers designed for measurements of small areas have a very

narrow FOV and measure temperatures of objects less than a tenth of an inch. For example, such

a thermometer held near a component on a pc board will measure the temperature of just that

component and ignore the components around it.


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7.0 Infrared Temperature Calculations

In order to obtain quantitative surface temperatures, raw thermographic data may need to be

extracted from the imaging system and processed in a separate mathematical program. The

image-processing component of the imaging system is used to extract data from the thermal

image and export them in appropriate arrays of text values to be synchronized with spatial

coordinates. The result for temperature at each data point should be calculated with the correct

emittance and a location-specific background level. The calculated IR temperature for the

reference emitter may be compared to direct contact measurements, and deviations may be used

to scale the rest of the IR data. Separate data sets may be merged together to combine data from

different views.

Equation given below, shows an expression for calculating a surface temperature, TIR, from the

total thermal radiation represented by the variable Te=1, the emittance of the surface, esurf, and the

background radiation level represented by the variable Tback. Te=1 is an equivalent blackbody

temperature for the surface being measured. Tbackis the equivalent blackbody temperature for the

background thermal radiation level as measured at each location with the aid of an applied

mirror. Values for both Te=1 and Tback are obtained from the thermographic system by setting

emissivity to unity. Conversely, setting emittance to less than one should cause the IR image-

processing component of the imaging system to process the image data using the calculation

using the equation,

This equation is used to determine both the apparent reference emitter temperature, TIR, Ref, (as

measured by IR imaging) and the apparent sample surface temperature, T IR, smpl. The difference


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between TIR,Refand the direct contact measured value, TDC,Ref, may be applied to correct TIR,smpl

and to arrive at the final IR surface temperature result, T. This correction should be made for

each temperature datum and for each IR image, to produce arrays of temperature values.

Final data sets merge spatial location coordinates with temperature values. The real distances

between location markers on the specimen are measured, and a coordinate system is used to

create temperature/location data pairs. The temperatures may be distributed linearly.

Temperature data are then made a function of spatial coordinates, mapped to the appropriate

coordinate system.

7.1 Infrared Temperature Uncertainty

The thermographer usually wants to estimate the uncertainty in temperature data. Errors in esurf

should be treated as a source of undefinable systematic uncertainty, esurf, and may be analyzed

by propagating uncertainty. Errors in Te=1 and Tbacklead to random uncertainties, Te=1 and Tback.

Te=1 and Tback are usually closely related to equipment specification for Noise Equivalent

Temperature Difference (NETD). To analyze error propagation, the sum of the squares of partial

differentials of Equation for TIR are calculated with respect to variables Te=1, Tback, and esurf,

which leads to one possible solution,as shown. The uncertainty in T IR, TIR, is then calculated

using Equation:

Values for both TIR,smpl and TIR,Ref are obtained using this equation. The uncertainty in the

direct contact measurement of the reference emitter surface temperature, T DC,Ref, is determined

from the overall system accuracy of the direct contact sensor combined with any errors

associated with adjustments that correct for gradients in the surface material. The uncertainty

arising from variations across the field of view, TFOV, is determined from the magnitude of

deviations in heavily averaged data for an isothermal plate that fills the section of the field of


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view being used. The uncertainty arising from non-linear performance or calibration of the

imager, TLin, is determined by evaluating TIR for a temperature controlled and separately

measured target for a range of temperatures and evaluating how deviations change over that

range. The total uncertainty in the measured surface temperature, T, is obtained from Equation :

8.0 TYPES OF INFRARED THERMOMETERS

The following is a convenient classification of IRTs:

Broadband thermometers

Band-pass thermometers

Narrow band thermometers

Ratio thermometers

Fiber optic thermometers

8.1 BROADBAND THERMOMETERS:

Broadband thermometers have usually been the simplest IRTs, with spectral responses from 0.3

microns wavelength to an upper limit of 2.5 to 20 microns (m), determined by the lens or

window material. They have been termed total radiation thermometers because, in the

temperature ranges of normal use they measure a significant fraction of all the thermal radiation

emitted by the object whose temperature is being measured.

8.2 BAND-PASS THERMOMETERS:

Band-pass thermometers were initially derived from simple, broadband thermometers. Lens,

window, or filter characteristics were selected to view only a selected portion of the spectrum.


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The 5 0.2m band-pass was used to measure glass surface temperature because glass emits

strongly in this region, but poorly below or immediately above this band.

8.3 NARROW BAND THERMOMETERS:

Narrow band thermometers operate over a narrow range of wavelengths. The spectral response

of many narrow band thermometers is determined by the optical filter used. Such narrow band

thermometers are used as general purpose instruments over the temperature range of interest. For

example, a thermometer using a silicon cell detector will have a response that peaks at 0.9m.

The upper limit of usefulness is about 1.1m. Such a thermometer can only be used at

temperatures above 600C (1100F).

8.4 RATIO THERMOMETERS:

A ratio thermometer measures radiated energy in two narrow bands and calculates the ratio of

the two energies. This ratio is a temperature-dependent function. The temperature measurement

is not primarily dependent on the energy in the two bands, only on the ratio of the two energies.

Therefore, any influence that affects the amount of energy in each band by the same percentage

has no effect on the temperature indication. Changes in target size have no effect. If the

emissivity of the target is the same at both wavelengths, the indicated temperature is not changed

by changes in emissivity. Unfortunately, this condition is not fulfilled by all oxidizable materials.

For other materials, the ratio techniques may reduce or eliminate changes in indicated

temperature caused by changes in surface finish. The ratio technique may reduce the effect of

energy absorbing materials such as particulates or C02 between the target and the thermometer,

if the percentage of absorption is the same at each wavelength.

8.5 OPTICAL PYROMETERS

Although optical pyrometers are no longer manufactured in significant numbers, there areprobably hundreds of thousands in everyday use, and they are sufficiently unique in design and

use to warrant a separate discussion. An optical pyrometer measures the radiation from the target

in a narrow band of visible wavelengths, centered at about 0.65 m in the red/yellow portion of

the spectrum. The most commonly used optical pyrometers are manually operated. The operator

sights the pyrometer on the target. At the same time he can see in the eyepiece the image of an


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internal tungsten lamp filament. The operator matches the filament color to the target by varying

the current through the filament with a rheostat, and when the target image and the tungsten

filament image are the same color, the target temperature can be read from a scale on the rheostat

knob. When the target and filament colors are the same, the filament image apparently vanishes,

so these pyrometers have also been called disappearing filament pyrometers.

8.6 FIBER OPTIC THERMOMETERSIn fiber optic thermometers, the infrared radiation from the target is guided to the detector by a

light guide. The first such sensors used a 1/8 in. diameter sapphire rod to pick up energy from the

target and transmit it to a detector. Contemporary fiber optics pyrometers use a flexible bundle of

glass fibers with or without a lens. The spectral response of these fibers extends to about 2 m,

though some exotic materials such as fluorides have a wider band pass. Some are useful at target

temperatures as low as 100C (212F). Fiber optic thermometers are especially useful where it is

difficult, dangerous or impossible to obtain or maintain a clear sighting path to the target, as in

pressure or vacuum chambers. Fiber optic thermometers have also been used to measure

temperatures of turbine blades in gas turbines, and the temperature of small objects in induction

heating coils.

9.0 ADVANTAGES AND DISADVANTAGES OF IR THERMOGRAPHY

The following points spell the advantages and disadvantages of this technique.


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9.1 Advantages:

It is a non-contact type technique. Fast, reliable & accurate output. Minimize preventive maintenance and troubleshooting time. Detect problems quickly, without interrupting service. A large surface area can be scanned in no time Presented in visual & digital form. Software back-up for image processing and analysis. Requires very little skill for monitoring.

9.2 Disadvantages:

Cost of instrument is relatively high. effects of thermal losses (convective, radiative, conductive) perturbing thermal contrasts Unable to detect the inside temperature if the medium is separated by

glass/polythenematerial etc.

10.0 Non-Destructive Evaluation (NDE)

10.1 Fast Transient NDE


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Fast transient thermal imaging is based on the time-evolution of surface temperatures on test

specimen during heating or cooling. Variations in temperature depend on the heat flow through

the object; heat flow is sensitive to cracks, delaminations, voids, and changes in material

properties. In a typical setup, flash equipment is used to generate a heat pulse, and the surface

temperature of the test specimen is monitored with an IR imager. The pulse duration and the total

energy delivered over the length of the pulse depend on the material properties and the nature of

the defect to be detected. A series of approximately 10 to 30 frames is recorded with frame rates

up to 80 Hz with scanners or 1 kHz with FPA imagers. In the absence of thermal pulse

equipment and a high speed imager, transient NDE can be successfully performed on some

specimens, particularly those with low thermal conductivity. Figure 6 shows several frames

taken at 10 second intervals after a steady IR heat source was applied to the back side of a

composite truck bed panel. The well bonded portions warm faster on the opposite, imaged side.

An image sequence like this can already be very informative when visually inspected by a

technician experienced in interpreting thermograms. However, image post-processing can greatly

enhance images and reveal features that are hidden in the unprocessed image. Post-processing

includes averaging of image sequences, coloration with different palettes, image subtraction and

edge enhancement. Complex processing is possible, including Fourier transformation of time

sequence images and tomography, if sufficient computer power is available to perform these

tasks. Tomography analysis translates the time image sequence into a three-dimensional object

sequence; defects can then be located in depth as well as in the image plane even though data are

collected only at the surface.


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Fig 10.1 Fast Transient NDE

The, white circle, horizontal stripes, and dots are the adhesive glue pattern between two layers of

a composite truck bed panel assembly. The pattern is relieved by the transient heat flow induced

by exposing the panel to radiant heat source on one side and imaging it from the opposite side

(10 seconds between each frame). The vertical lines are due to corrugated surface of the panel.

10.2 Steady-state NDE

Fast transient thermography can provide a more robust non-destructive evaluation technique than

steady-state thermography, but its use has been limited because it requires expensive thermal-

pulse equipment and storage of a large number of data for each specimen. Steady-state IR

thermography, by contrast, is much less expensive, requiring minimal equipment and data

storage. Near steady-state thermography could be used for NDE during production phases where

temperature cycles have been applied to parts, for example the cool-down period after paint

baking, adhesive curing, or injection molding of plastic parts. The required temperature

difference between the part to be evaluated and the environment depends on the material,


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geometry, and size of the part; the size and nature of the defects being sought; and the minimum

resolvable temperature difference of the IR imager being used. This difference can be as small as

a few degrees Celsius. For example, the figure shows an IR thermogram of a composite truck

bed panel after reaching steady state with a radiant heat source. Gradients are not as sharp in fast

transient thermography when imaging materials with high thermal conductivity. Post processing

can improve image quality as shown in the image to the right.

Fig 10.2 Steady state NDE

11.0 APPLICATIONS

Infrared Thermal Imaging is an excellent condition monitoring tool to assist in the reduction of

maintenance costs on mechanical equipments. The technique allows for the monitoring of


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temperatures and thermal patterns while the equipment is online and running under full load.

Most mechanical equipment has allowable operating temperature limits that can be used as

guidelines. Unlike many other test methods, Infrared Thermal Imaging can be used on a wide

variety of equipment including pumps, motors, bearings, pulleys, fans, drives, conveyors etc.

This section will explain the benefits of Infrared Thermal Imaging as a condition monitoring tool

for plant mechanical systems.

11.1 IMPROVED TROUBLESHOOTING

Infrared Thermal Imaging definitely should be one of the tools that are selected for motor and

rotating equipment inspection. Thermographic examination can help technicians use the other

tools, such as vibration analysis, more effectively. If a thermal anomaly is found, then the other

tools can be employed to help isolate the cause of the problem.

11.1.1 MOTORS AND GENERATORS

When considering electric motors and generators, operating temperatures and thermal patterns

can be a valuable key in a predictive maintenance program. All motors have a normal thermal

pattern as well as given maximum operating temperature. This temperature is usually stated on

the nameplate of the motor and is normally given as a rise in degrees C above the ambient air

temperature. Most motors are designed to operate in ambient temperatures that do not exceed 40

C. Conditions such as inadequate air flow, partial discharge, unbalanced voltage, bearing failure,insulation failure and degradation in the rotor or stator can be identified with an Infrared Thermal

Imaging monitoring program. Abnormal thermal patterns can also identify misalignment in

couplings when these devices are used in conjunction with motors. Figure shows the thermal

patterns of two motors, where there is a marked overall temperature rise on the motor on the left,

indicating a possibility of abnormal operation.


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Fig 11.1 IR imager of motor

11.1.2 BELTS AND PULLEYS

Belts and pulleys are good candidates for Infrared Thermal Imaging inspection. The interaction

of the pulley wheel and the belt generates friction as the belt contacts and then leaves the pulley

surface. Additionally, the continuous tension and compression of the belt causes internal friction.

Both of these processes result in heat being generated which can be seen with the infrared

camera. Comparing the thermal patterns of several pulley belt systems can provide clues to

improper operation. The temperature distribution across a pulley sheave should be uniform if

everything is working as intended.

Fig 11.2 IR Image of pulley

11.2 PROVIDE EVIDENCE OF PROPER INSTALLATION

11.2.1 BEARINGS


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Bearing problems are generally found by a comparison of surface temperatures; comparing one

bearing to another working under similar conditions. Overheating conditions are documented as

hot spots within the infrared camera and are usually found in comparing equipment to

equipment, end bell to end bell (for the same type of bearings) and stator to end bell temperatures

(determined by motor design and configuration).

Fig 11.3 IR Image of bearing

Vertical motor pump combination displaying elevated temperature in lower thrust bearing.

11.3 REDUCE OPERATING COSTS(Leaking or Blocked Pipes and Valves)

11.3.1 STEAM TRAPS

Steam is an efficient way to transport heat energy. The latent heat needed to transform water into

the gaseous state, steam, is extremely large. This means that large amounts of heat energy can be

transported with a minimum temperature differential to the environment. This equates into lower

energy and insulation costs.

When steam arrives at the site where heat energy is needed, it condenses, thereby releasing the

large latent heat it was carrying. The condensate formed by this process must be removed by the


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steam system and returned to the boiler where it is turned back into the steam and the cycle is

repeated.

The steam trap performs this function; to hold back live steam while allowing gases and

condensate to pass through. This allows more energy to be obtained from the steam, thus raising

a steam system's overall efficiency.

Fig 11.4 IR image of steam trap

In these two photos of steam traps, the Infrared Thermal Imaging photo on

the left shows the point of leakage.

Steam traps, like any mechanical device, eventually fail. Most are designed to fail in the open

position to maintain steam system operation. When they fail in the open position, they "blow"

live steam. This costs energy dollars which the steam trap was installed to conserve.

Occasionally, steam traps fail in the closed position. This causes condensate back up in the steam

system with potentially disastrous results.

Fig11.5 IR image of faulty steam trap


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Thermogram and visible image of a failed inverted bucket steam trap.

Properly performed Infrared Thermal Imaging can identify steam traps that are blowing steam as

well as those that may fail closed. Steam traps are sometimes located in inconvenient areas

where they are hard to reach using other NDT technologies. This fact makes trap diagnosis by IR

especially useful.

11.3.2 FURNACE & REFRACTORY

A refractory material is basically a high temperature insulator. They are usually a non-metallic

ceramic type of material and are commonly supplied in brick form. Refractory materials are used

inside furnaces, ovens, boilers, hot storage tanks and other equipment that produces or contains

extremely hot temperatures.

Using Infrared Thermal Imaging to inspect refractory begins with the assumption that a uniform

temperature inside a vessel will result in uniform warming of its exterior as heat is conducted to

the vessel's walls.

An ideal vessel would have a perfectly uniform temperature on its external surface. If a crack or

other defective conditions existed in the insulating medium, the exterior surface would increase

in temperature in direct proportion to and in the exact location of the defect. Thus, the defect

would be obvious based on the non-uniform conductance of heat into the exterior surface. If the

exterior metal is threatened or a safety hazard may exist, absolute temperature measurements ofthe hot areas become important.

In normal practice, there are other structural variations which cause non-uniform heat patterns in

addition to the defects; these include grid work, refractory type variations, port holes, catwalks,

etc.

11.3.3 ROTARY KILNS

In the manufacture of cement the raw materials are ground together, the mixture is heated until it

fuses into a clinker, and the clinker is ground into a fine powder. The heating is usually

accomplished in rotary kilns which look like huge rotating pipes, sometimes hundreds of feet

long. The kilns are slightly tilted from the horizontal, and the raw material is introduced at the

upper end, either in the form of a dry rock powder or as a wet paste composed of ground-up rock

and water. As the charge progresses down through the kiln, it is dried and heated by the hot gases


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from a flame at the lower end. After it leaves the kiln, the clinker is cooled quickly and ground,

and then conveyed by a blower to packing machinery or storage silos.

Fig 11.6 IR image of rotary klin

Thermal patterns indicate refractory damage in this lime kiln.

The refractory lining of the kilns eventually wears out and must be replaced. If it is not, the steel

shell can overheat and fail. Infrared Thermal Imaging is ideally suited for locating and measuring

the temperature of areas where refractory has failed. Continuous tracking allows the kiln

operators to maximize the amount of time they can operate until a shutdown for refractory repair

is necessary.

11.4 IMPROVE THE EFFICIENCY OF A PROCESS

11.4.1BLOWER SYSTEMS

Blower systems can be used to move materials through pipes from one process or location to

another. An example might be a system to deliver coal dust to a boiler. The condition of the

pipes and process itself can often be monitored with an infrared camera. Buildup of product

debris in a pipe will usually show up as a temperature differential in a section of pipe. After the

buildup has been removed, Infrared Thermal Imaging can be used to verify that the work hasbeen completed satisfactorily.


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Fig 11.7 IR image of blower pipe

Product buildup can be clearly seen as the cold area

on the bottom of the pipe.

11.5 OTHER APPLICATIONS

11.5.1 Automobile industries

Infrared thermometers are used extensively in the automotive industry to diagnose problems

ranging from air conditioning, brakes, to engines. They also help in avoiding dangerous car

interiors by convenient temperature measurement with these non-contact devices. They are

however most effective in diagnosing temperature-related engine problems. This is because, as

with other traditional thermometers, the user doesn't have to dissemble the whole engine, as it

reaches even inaccessible areas. Among the various uses of these infrared thermometers in

engine and exhaust troubleshooting are for scanning manifold temperature to determine low

compression, for misfire condition, measuring and comparing exhaust system components for

correct fuel/air mixture and for scanning both sides of the catalytic converter for temperature

differences

These are also used for cooling system diagnostics like checking for overheating problems,

scanning radiators for core restrictions, measuring thermostat temperature and above all for

measuring coolant temperature sensors and manifold air temperature sensors


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Even for measuring climate control, in automobiles infrared thermometers are used most of the

times. With them you can check heaters, air conditioners, and vents at a convenient pace for any

kind of malfunction or system output. These are equally powerful like digital multimeters, as

gauging instruments.

Further, infrared thermometers are used for checking the condition of braking system in

automobiles. This is very necessary because if the temperature is significantly higher than

ambient or varied temperatures of rotors, drums or bearings, it would indicate excessive wear.

Uneven braking can also be diagnosed with this amazing instrument.

11.5.2 Steel industry

Steel industry use thermometer because products are moving, the temperature is very high.

Ordinary steel industry application is temperature is a constant state of molten steel is beginning

to change into pieces. With the same temperature to heating steel is preventing it from the

deformation of the key, infrared thermometeris used to measure the internal temperature of the

regenerator. In high temperature spin rolling grinding machine, the infrared thermometer was

used to identify of product temperature is in rotating limits. In cooling grinding machine, infrared

thermometer rolling in steel cooling process monitoring steel temperature.

11.5.3 Glass industry

In glass industry, products are in the dynamic state, which is to be heated to a high temperature.

Infrared thermometer used to monitor the temperature of furnace. Portable sensors are used to

detect by measuring the external temperature points. Measurement of the temperature during

melting of glass is used to determine proper mouth furnace temperature. On the flat glass,

sensors in each processing phases are used for testing temperature. Wrong temperature or

excessive temperature change can cause uneven expansion or contraction. For bottles and

container products, it would undergo melt flow to keep the glass at the same temperature before

furnace. Infrared thermometer is used to detect the glass before furnace temperature. So it in

export place should be the proper state. In fiberglass products, infrared sensor is used in
http://www.temperature-controller.info/categories.php?id=6http://www.temperature-controller.info/categories.php?id=6


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processing furnace detection of glass furnace temperature before. Infrared sensor in glass

industry another use is used in windscreen products process.

11.5.4 Plastic industry

In the plastic industry, infrared thermometer is used to avoid defiled product, by measuring

temperature profiles of dynamic objects. In blown film ejective process, temperature

measurements can be successfully performed with ease using an infrared imager to adjust

heating and cooling which can help to keep plastic tension completely distributed along its

thickness. Also in the case of film made in cast out process, sensors help control temperature to a

large extent. In chip pressure out, the sensor can let operator to adjust extinguished heater and

cold roll to guarantee the quality of its products. Infrared thermometer in preventive

maintenance, uses portable heat display system, maintain personnel can identify potential or

already existing problems. For example: the engine overheat, transformer winding of plugged

cooling fins, capacitance contact undesirable, heat in a compressor cylinder lid rally. Any

problems are accompanied with temperature, or temperature curve with surrounding temperature

completely not, so can use portable heat display system positioning. In most cases, when asked

to stop process before, can be timely find out problems, and timely correcting.

11.5.5 Chemical industry

In petrochemical industry, refineries in routine preventive maintenance program, uses

temperature display system. These programs include furnace process monitoring and several

confirmations. In furnace processes, infrared heating tube displays are used to detect rally carbon

ratio. These are called coking rally, which may lead to a melting pot of higher DianHuoLv. The

high temperature condition will reduce the life of the pipes used. This condition can be

controlled to a large extent by incorporating infrared thermometer detectors in the vulnerable

sites.

There are many more instances besides those mentioned previously for which thermography can

be utilized. Here are a few:

11.5.6 Aerospace Applications


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Water ingress in airplane control surfaces and radomes Tire and brake system diagnosis Windshield and wing surface deicing system diagnosis Stress crack and corrosion identification and location Jet and rocket engine analysis Composite materials delamination and disbanding location Target signature analysis

11.5.7 Petrochemical Applications

Refinery process line insulation loss or leak detection Refinery process evaluation Heat exchanger quality and efficiency evaluation Furnace refractory (insulation) inspections Furnace internal flame evaluation and tube inspections Flame propagation explosion analysis

11.5.8 Research and Development Applications

Design prototyping evaluation

11.5.9 Pulp and Paper

Detect uneven heat distribution in Fourdrinier steam boxes Identify wet streaks, nonuniformity that can have adverse effects on paper quality Identify basis weight variations Monitor size press performance Analyze dryer temperatures to look for nonuniformity in dryers Monitor coating to see that it is being applied uniformly to surface of the paper Analyze reel to find anomalies that may be induced by pieces of process equipment

connected to the paper machine

Inspect chip piles for hot spots

11.5.10 Mechanical Systems


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Boilers Inspect burners for flame impingement and burner management Look at combustion patterns of fuel Detect thermal patterns on boiler tubes and measure tube skin temperature during normal

operation or when boiler is on standby

Scan and record temperatures in areas of boiler not monitored Scan the exterior of boiler for refectory damage or locate warmer areas where potential

refectory damage may occur

Detect coke buildup in crude oil furnaces Power plant boiler flue gas leak detection Mechanical bearing inspections Heat, ventilation, and air-conditioning equipment evaluation Cold storage cooling losses Detect insulation leaks in refrigeration equipment

12.0 CONCLUSION

This seminar provides a summary of infrared thermographic systems. The theory of operation,

which is based on measuring blackbody thermal radiation, and the fourth power temperature

dependence of emitted IR energy, demonstrates the strong signal inherent to this sensing

technology and hence, the high temperature resolution that is achievable. There are various types

of IR imaging systems. All of them generate images that represent the surface temperatures of an

object, but they can be comprised of a variety of detector materials, each with unique spectral-

physical properties, which makes it important to select the proper detector technology for a

particular application. There are two major families of optical design, focal plane array imagers

and motorized scanning mirror based imagers. For successful IR imaging, it is essential to be

aware of the surface property emittance. Knowledge of surface emittance, in the spectral band of

the imager being used, allows the thermographer to distinguish the emitted portion of the

measured radiation from the reflected portion. The thermal setup and environment also require

special considerations for successful thermography. The thermographer often manipulates the


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overall heat transfer situation that leads to the temperature differences imaged on the specimen of

interest in order to produce the most accurate and informative thermal data. Scientific

temperature mapping is a methodology that improves upon the absolute accuracy of quantitative

thermography. The procedures employed include external referencing targets and background

mirrors. Typical applications of IR imaging include: thermographic inspection for predictive

maintenance, medical imaging, non-destructive materials testing, and building component

testing.

13.0 Future of IR imaging

The future of IR imaging will likely see many more applications emerge, as this powerful

technology becomes more accessible with less expensive and more compact equipment. New

detector types such as microbolometers, QWIPS or direct sensing optical systems (change of

refraction due to temperature) will become more prominent. IR imagers will be substantially

smaller and more portable with reduced power requirements, as a result of compact focal plane

array optics and not being burdened by providing cryogenic cooling for sensors. Increasing

computing power will make image analysis and processing possible for online usage. Image

resolution of focal plane arrays is expected to rise. Mega-pixel arrays will likely be available for

thermal imaging. Faster image acquisition speeds will open a new world of diagnostic

possibilities for very fast thermal phenomena such as combustion or blasting technology. The

various detection mechanisms may make IR imagers even more specialized for their intended

application. Selecting the appropriate technology for the job will continue to be important. For

instance, an imager with a very high frame rate may lack the ability to make absolute

temperature measurements as accurately as an imager designed for slower phenomenon, where

absolute accuracy is most crucial. Overall, there is much to be learned by seeing temperatures


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with an IR imager, and this capability is likely to grow more powerful, and become more

accessible, in the future.

14.0 References

Carlomagno, G. M., Heat Transfer Measurements by Means of Infrared Thermography,In Measurement Techniques, von Karman Institute, Lect. Series 2005-09, pp. 1-114,

Rhode-Saint-Gense, Belgium, 2009

The Encyclopedia of Imaging Science and Technology by Joseph P. Hornak, Editor-in-Chief, John Wiley and Sons.

De Luca, L. and Cardone, G., MTF Cascade Model for a Sampled IR Imaging System,Applied Optics, vol. 30, pp. 1659-1664.

H. Kaplan, Practical Applications of Infrared Thermal Sensing and Imaging Equipment,Second Edition, Proc. Soc. of Photo-Opt. Instrumentation Eng. (SPIE), TT34, 160, 2003.

D. Turler, B.T. Griffith, D. Arasteh. Laboratory procedures for using infraredthermography to validate heat transfer models. Insulation materials: Testing and

Applications: Third Volume ASTM STP 1320. R. S. Graves and R. R. Zarr, ed.

Philadephia, PA, American Society for Testing and Materials, 2001

B.T. Griffith, H. Goudey, D. Arasteh, Infrared Thermography Measurements ofWindow Thermal Test Specimen Surface TemperaturesASHRAE Transactions ?(not yet

published) American Society of Heating, Refrigeration and Air-Conditioning Engineers

Inc., 2002

V. Vavilov, X. Maldague, J. Picard, R.L. Thomas, L.D. Favro, Dynamic thermaltomography: New NDE technique to reconstruct inner solids structure by using multiple


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IR image processing, Review of Progress in Quantitative NDE, D.O. Thompson and

D.E. Chimenti ed., Brunswick, Maine, 1991, 11A, Plenum Press, 1999, pp. 425-432

X. Maldague, P.O. Moore, Infrared and Thermal Testing. American Society for Non-destructive Testing, 3

rdEd. Columbus Ohio, 2006

Internet:http://www.infrared institute.com

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