Ultrasonic

• Advantages– Non-Contact: Nothing touches the target object– Measures Distance: The distance to the target is

measured, not just its presence– Long and Short Range: Objects can be sensed

from 2 inches to 37 feet– High Resolution: Precise discrimination of target

position changes– Proportional Outputs: All analog, switch and

data outputs are range dependent– Ambient Light Levels: Unaffected by ambient

light levels

– Optical Characteristics of Target: Unaffected by the transparency, reflectivity, opacity or color of the target object

– Surface Characteristics: Target surface texture is generally not a problemGeneral Specifications apply to all Senix products. Refer to specific models for detailed specifications.

– Range: Compact and Modular models as close as 5 cm (2 inches) and as far as 1128 cm (37 feet), other models vary.

– Power Input: DC all models, AC input options available for Modular sensors

– Beam Angle: Conical shape, 15 degrees total angle unless otherwise noted

– Adjustment: All models are push-button adjustable for basic setup.

– Update Rate: 20 Hz nominal, adjustable from 2 to 120 Hz on PC-configurable models

LVDT

LVDT stands for linear variable differential transformer. An LVDT is a noncontactinglinear displacement transducer that works on the principle of mutual inductance, producing an electrical signal that is proportional to the position of a separate moving core (or armature).

The fundamental advantages of LVDTs are their high degree of robustness, infinite resolution, and ability to operate at high temperatures and in extreme environments.

Centering the core with respect to the two secondary windings gives them the same magnitude of induced voltages, but the polarity, or phasing, will be opposite. When the core is displaced from this null position, the output amplitude on one secondary coil (Va) increases, while the output amplitude on the other coil (Vb) decreases.

These voltages can be used individually or combined to produce an output signal proportional to position, dependent upon the method of demodulation employed.

The following are the two main methods used.

• Ratiometric Operation

• Differential Operation

Ratiometric Operation

• A highly accurate method of translating the LVDT output is to measure the secondary voltages independently to generate a ratio of the difference divided by the sum of these values

Ratiometric operation improves the following:

• Immunity to LVDT supply voltage and frequency variations

• Immunity to errors due to temperature effects on LVDT sensitivity

• Frequency and phase response • Immunity to common-mode noise on LVDT lines • Transducer interchangeability

• Additionally, the sum of the secondary output voltages (Va + Vb) is nominally constant throughout the LVDT stroke range, so it can be used for system error detection in high-integrity systems.

• Operating in the ratiometric mode requires a five- or six-wire, center-tapped LVDT specifically designed for the purpose.

Differential Operation

LVDTs are normally available with either four or five wires; the extra wire is the center tap in the output. When operating in differential mode, this center-tap connection is often not used.

In this connection configuration, when the core is displaced from the center null position, the output will increase in-phase with the input in one direction and antiphasewith the input in the other.

When using LVDTs in the differential mode, changes in supply voltage, operating temperature, and supply frequency will directly affect the output, lowering its accuracy.

Hall Effect

The "Hall Effect" is named after Edwin Hall who discovered the effect in 1879. The basic "Hall Effect" sensing element is a semiconductor device which, when biased by an electrical current through it, will generate an electrical voltage proportional to the magnitude of a magnetic field flowing perpendicular to the surface of the semiconductor.

The voltage generated is very small and must be amplified and signal processed to provide a useful output from the sensor.

Unipolar Head-On. Very sensitive, but non-linear over large distances (consequently linear over very tiny distances). Well-suited to measuring tiny deflections. Note that perpendicular magnetic flux is required for greatest sensitivity!

Three-magnet Bipolar Slide-by. Keep the distance constant, and the motion of the magnets can be detected with extreme sensitivity. Calibration is problematic but the setup provides extreme sensitivity if operated on the steep part of the distance/gauss curve.

Unipolar Slide-by. Probably most useful for alignment and orientation. For small distances, the distance/gauss slopes are linear to either side of the null point and can be calibrated.

Bipolar slide-by (1 Magnet). The magnet can also be a linear bar type. Good linear region in the middle of the distance/gauss relation that can be accurately and repeatablycalibrated.

Bipolar slide-by (2 Magnets). The magnet can also be a linear bar type. Long linear region in the middle of the distance/gauss relation that can be accurately and repeatablycalibrated. This principle is used in many commercial Hall-effect-based linear distance sensors.

Bipolar Slide-by (Ring Magnet). Useful fortransducing rotation. Keep the gap constant, as with all slide-by techniques.

Photoconductors

Photoconductors are made from semiconductors that have been heavily

doped n-type or p-type and are frequently used for infrared detection

The resistance of an infrared photoconductive detector can be as little as 10 Ω or as much as 10 MΩ

Photoconductive detectors are usually operated by biasing them with a fixed

voltage and measuring the current flowing in the biasing circuit. The

current in the absence of radiation is called the dark current.

Photoconductors are frequently, but not always, polycrystalline materials. That

is, instead of being one big single crystal, the detector is made up of a

number of smaller crystals.

Photodiodes

A diode consists of a region of single crystal semiconductor materialthat has been doped n-type in

contact with a region of the same material that has been doped p-

type.

Photodiode junctions are unusual because the top "p" layer is very thin.

The thickness of this layer is determined by the wavelength of

radiation to be detected.

When light is absorbed in the active area an electron-hole pair is formed. The electrons and holes are separated

electrons passing to the "n" region and holes to the "p" region. This

results in a current generated by light (usually abbreviated Isc). The

migration of electrons and holes to their respective region is called "The

Photovoltaic Effect".

The materials most commonly used for infrared photodiodes are InSb and

HgCdTe while wider bandgapmaterials such as silicon and SiC are

used for shorter wavelength detection.

Strain Gauges

The most universal measuring device for the electrical measurement of

mechanical quantities is the strain gage. Several types of strain gages

depend on the proportional variance of electrical resistance to strain: the

piezoresistive or semi-conductor gage, the carbon-resistive gage, the bonded metallic wire, and foil resistance gages.

Example of Strain Gauge In work