Week 10 Slide Note

7/28/2019 Week 10 Slide Note

1/35

Transducers

- Classification and selection

- Primary Sensing Element


2/35

Transducer

A measuring device, to convert none-

electrical variable into electrical

variable and vice versa

SensingElement

TransductionElement

Non-electricalquantity

SensorResponse

ElectricalSignal


3/35

Classification:

1. Basic of transduction principle used

2. Active and passive3. Analog and digital

4. Primary and secondary

5. Common and inverse

Transducer


4/35

Basic of transduction principle used

How the input variable is being converted intocapacitance or resistance or inductance values

Classification
http://www.google.com.my/url?sa=i&rct=j&q=resistive+transducer&source=images&cd=&cad=rja&docid=cUKdPRR-QIm5iM&tbnid=A3IaeZrsrDgu3M:&ved=0CAUQjRw&url=http://pubs.usgs.gov/twri/twri8a3/&ei=-3JvUaK3CM-zrAfw3YGIBQ&psig=AFQjCNE_np5uVHN8lw0x7QFGSmzUv1enHQ&ust=1366344688682792


5/35

Active and Passive

No any external excitation to provide the

output.

Required an external excitation for passive.

Classification


6/35

Analog and Digital

Producing the output in analog and digital formrespectively

Classification


7/35

Primary and SecondaryMeasuring and converting a variable into

another variable and whose output forms the

input of another transducer.

Converting the output of first transducer into an

electrical signal.

Classification


8/35

Usual and Inverse

Measuring and converting an electrical variable

into non-electrical variable

Classification


9/35

Exercise !!!

What is a pressure transducer? A pressure transducer,sometimes called a pressure transmitter, is a transducerthat converts pressure into an analog electrical signal.Although there are various types of pressure transducers,

one of the most common is the strain-gage basetransducer. The conversion of pressure into an electricalsignal is achieved by the physical deformation of straingages which are bonded into the diaphragm of thepressure transducer and wired into a wheatstone bridge

configuration. Pressure applied to the pressuretransducer produces a deflection of the diaphragm whichintroduces strain to the gages. The strain will produce anelectrical resistance change proportional to the pressure.


10/35


11/35

Selection1. Operating principle

2. Operating range

3. Accuracy4. Sensitivity

5. Stability and reliability

6. Usage and ruggedness

7. Transient and frequency response8. Loading effect

9. Electrical parameters

Transducer


12/35

Operating principle

Basically the transducers are selected based on their

operating principle. Examples of operating principles

used by the transducers are resistive, capacitive,

piezoelectric, inductive, up to electronic principle etc.

Spec

Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/Manometer%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Manometer%20spec.pdf


13/35

Operating range

This factor is considered so that the transducer should

be able to function within the specified range with

good resolution. Every transducer should be providedwith some rating within which there will be breakdown

in its function

Selection


14/35

Accuracy

It is one of the most desired characteristic of any

transducer. If the transducer doesn't needs frequent

calibration, it must have high degree of accuracy and

repeatability. Because errors may occur due to the

sensitivity of the transducer to other stimulations

Spec

Selection


15/35

Sensitivity

It is also a desired characteristic of a transducer. Every

transducer should be sufficiently sensitive to provide

some output that can be sufficient and detectable

Spec

Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/Force%20sensor%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Force%20sensor%20spec.pdf


16/35

Stability and reliability

The transducer should have high degree of stability

during its function and also storage life. It should also

have a high degree of reliability

Selection


17/35

Usage and ruggedness

The ruggedness, size and weight of a transducer should

be chosen depending on the application in which it is

used

Selection


18/35

Transient and frequency response

The transducer should have required time domain

specifications such as, settling time, rise time, peak

over shoot and small dynamic error etc

Spec

Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/piezo%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/piezo%20spec.pdf


19/35

Loading effects

The transducers should undergo minimum loading

effect so that if can provide accurate measurement.The parameters of a transducer are that, which

characterize the loading effect is its input and outputimpedance. lt is considered in order to get minimum

loading effects (Which can be neglected). For minimumloading effect the transducer should have low output

impedance and high input impedance

Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/Force%20sensor%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Force%20sensor%20spec.pdf


20/35

Electrical parameters

The type and length of cable required, signal to noise

ratio in case the transducer is used with amplifiers and

frequency response limitations should also be

considered

Spec

Selection


21/35

Selection


22/35

Sensing Element

Sensing

Element

Transduction

Element

Non-electrical

quantitySensor

Response

Electrical

Signal


23/35

Capacitive Sensors- Consists of two parallel metal plates.

- There is either air or some others mediumbetween the plates (dielectric).

- Given,

- To detect displacement by applying moveableplates

- Capacitive displacement forms part of measuringpressure, sound or acceleration

- Also, can detect liquid level if the

dielectric is part liquid

Sensing Element


24/35

Resistive Sensors

- Operating in variation of the resistance.

- Temperature measurement using thermistor.- Displacement measurement using

piezoresistive sensors

Sensing Element


25/35

Magnetic Sensors

- Utilize the magnetic phenomena of

inductance, reluctance and eddy current.

- By moving the T core, current on the coil

changed.

Sensing Element


26/35

Hall-Effect Sensors

- To measure the magnitude of a magnetic field.

- V = KIB, where K is known as Hall constant.- The magnitude of the field changes when the

device come close to any ferrous metal object

as application in proximity sensor.

Sensing Element


27/35

Strain Gauges

- Changing in resistance when stretching andstraining.

- Able to detect very small displacement, 0-50m.

- Its consists of a length of metal resistance wire

formed into a zigzag pattern and mountedonto a flexible backing sheet.

- Gauge factor = R/S

Sensing Element


28/35

Piezoresistive Sensors

- Made from semiconductor material, P-typeregion has been diffused into a N-type base.

- Producing higher gauge factor.

- Proper piezoelectric strain gauges also knownas semiconductor strain gauges.

Sensing Element


29/35

Optical Sensors

- Air path, to measure proximity, translational orrotational motion and gas concentration.

- Fiber optic path, 2 major classes intrinsic andextrinsic sensors.

Sensing Element


30/35

Ultrasonic Sensors

- The most common element is a piezoelectric

crystal.

- It can operate interchangeably as either a

transmitter or a receiver.

- The principle operation is an AC voltage

generates an ultrasonic wave and vice versa.

Sensing Element


31/35

Nuclear Sensors- The basic operation is quite similar to optical sensor.

- Caesium-137 is used commonly as a -ray source,

and a sodium iodide device is used commonly as a -ray detector.

- To measure a level

of liquid in storage tanks.

Sensing Element


32/35

Microsensors- In millimeter-sized, two and three-dimensional

micromachined structures.

- To measure temp, pressure, force, acceleration, humidity,

magnetic field, radiation and chemical parameters.- Usually, constructed from a silicon semiconductor material.

- Radiation microsensors are made from silicon p-n diodes oravalanche photodiodes.

Sensing Element


33/35

Conclusion

Most non-electrical parameters can be

measured by electronic instruments. The

parameters will be detected and then

interpreted/converted to voltage or current informs of analog or digital techniques.

Combination of the task are operated using

transducers. Sometime, the operating withindividual device but others in cooperation.


34/35

Thank You, See Again


35/35

Spot Test

1. What is transducer?

2. Write the classifications of transducers?

3. What parameters should be considered in

selecting a transducer?

4. Write short notes on strain gauge sensor?

Week 10 Slide Note

Documents

Transcript of Week 10 Slide Note