1. ELECTRONIC INSTRUMENTATION
EKT 314/4
WEEK 3 : CHAPTER 2
TRANSDUCERS

2. Chapter 2 Problem Statement
Don’t know what is Transducer and its functions.
Not clear the difference with Sensor
What actually transducer measures?
How many variety of transducers available actually?
Is there any way of grouping transducers?

3. Chapter 2 Objectives To get clear definition of transducer
To know how transducers are classified
To list common electrical transducer parameters
To know electric transducers advantages/disadvantages
To classify electrical transducers and how to select the appropriate one to apply.

4. Contents Definition of Transducer Type of Transducers
Electrical Transducers
Parameters
Advantage/Disadvantages
Classification
Application
Selection of Transducers
Principle & Example of Transducers

5. Transducers: Definition
A device that receives energy from one system and transmit it to another, often in different form.
A device capable of being actuated by an energizing input from one or more transmission media, and in turn, generating a related signal to one or more transmission systems or media.

6. Definition Explanation
Device that convert energy from one physical form into another
Physical variable into signal variable
Input measurand may be a physical or mechanical quantity, property or conditions.
Output may can be electrical, mechanical or acoustical.
Terminology differentiation
Sensor – input transducer
Actuator – output transducer

7. Contents Definition of Transducer Type of Transducers
Electrical Transducers
Parameters
Advantage/Disadvantages
Classification
Application
Selection of Transducers
Principle & Example of Transducers

8. Type of Transducer
Mechanical Transducers
Electrical Transducers

9. Type of Transducer Mechanical Transducers Electrical Transducers
High accuracy, ruggedness, relatively low cost and operate without any external power supplies.
Poor frequency response, require large force to overcome mechanical friction
Cannot provide remote control or indication mechanism
Electrical Transducers

10. Contents Definition of Transducer Type of Transducers
Electrical Transducers
Parameters
Advantage/Disadvantages
Classification
Application
Selection of Transducers
Principle & Example of Transducers

11. Electrical Transducers
Sensing device that transform the physical, optical or mechanical quantity measurement directly to the electrical voltage or current relative to the input measurand.
Conversion of non-electrical quantity into electrical signal by the transducers may need it to be in two parts:
Sensing element – part that respond to the changes in the physical quantity.
Transduction element – part that transform the output from sensing element into electrical signal.

12. Contents Definition of Transducer Type of Transducers
Electrical Transducers
Parameters
Advantage/Disadvantages
Classification
Application
Selection of Transducers
Principle & Example of Transducers

13. Electrical Transducer Parameters
Sensitivity
Electrical output per unit change in the input measurand.
Linearity
Linear relationship between physical parameter and electrical signal
Dynamic Range
Can be used under wide range of measurement conditions.

14. Electrical Transducer Parameters
Repeatability
Input output relationship should be constant and predictable over a period of time
Physical Size
Physically minimal in weight and volume

15. Contents Definition of Transducer Type of Transducers
Electrical Transducers
Parameters
Advantage/Disadvantages
Classification
Application
Selection of Transducers
Principle & Example of Transducers

16. Electrical Transducer Advantages
Electrical amplification and attenuation can be done easily.
Output can be recorded and indicated remotely.
Output can be modified to meet the requirements of indicating or controlling units.
Signals can be conditioned and mixed to obtain any combinations.

17. Electrical Transducer Advantages (cont.)
Miniaturization due to size and shape of electrical transducers.
Contour design and dimensions can be chose no to disturb measurand phenomenon.
Low power required to control the system.
Effects on friction are minimized.
Mass-inertia effects are minimize.

18. Electrical Transducers Disadvantages
Low reliability due to ageing and drift of the active components.
Can be expensive when associated with the signal conditioner.
Less accurate and resolution (in some cases).

19. Contents Definition of Transducer Type of Transducers
Electrical Transducers
Parameters
Advantage/Disadvantages
Classification
Application
Selection of Transducers
Principle & Example of Transducers

20. Classification of Electrical Transducers
Two categories:
Active
Self generating devices
Generates electrical signal directly in response to the physical parameter.
Does not require external power source.
Passive
Operate under energy controlling principles.
Requires external electrical source.

21. Transducer Classification
Active
Passive
Resistive
Inductive
Capacitive
Photoconductive
Piezoresistive
Magnetoresistive
Thermoresistive
Elastroresistive
Hall Effect
Synchro
Gyro
Radio-active absorption
Ionic Conduction
Thermoelectric
Piezoelectric
Photovoltaic
Magnetostrictive
Electrokinetic
Electrodynamic
Electromagnetic
Pyroelectric
Galvanic

22. Active Transducers Type of Transducers Electrical Parameters
Principle of Operation
Thermocouple and Thermopile
Voltage and Current
EMF is generated across the junction of two different metals or semiconductors when that junction is heated.
Photovoltaic
Voltage is generated across semiconductors junction device when radiant energy stimulated the cell.
Piezoelectric Pickup
EMF is generated when external force is applied to certain crystalline materials, such as quartz.
Moving Coil Generator
Voltage is generated from the moving of coil in magnetic field.

23. Passive Transducers Type of Transducers Electrical Parameters
Principle of Operation
Photomultiplier Tube
Voltage and Current
Secondary electron emission due to incident radiation on photosensitive cathode.
Photoemissive Cell
Electron emission due to the incident radiation upon photo emissive surface.
Hall Effect Pickup
Potential difference generated across a semiconductor plate when magnetic flux interacts with the applied current.
Ionisation Chamber
Electron flow induced by ionization of gas due to the radioactive radiation.

24. Passive Transducers (cont.)
Type of Transducers
Electrical Parameters
Principle of Operation
Potentiometer
Resistance
Variation of resistance in a potentiometer or bridge circuit due to the positioning of the slider by and external force.
Thermistor
Resistance of certain metal oxide with negative temperature coefficient of resistance varies with temperature.
Photoconductive Cell
Variation of resistance of a cell as a circuit element with incident of light.
Resistance Hygrometer
Variation of resistance of a conductive strip with moisture content.

25. Passive Transducers (cont.)
Type of Transducers
Electrical parameters
Principle of Operation
Dielectric Gauge
Capacitance
Variation of capacitance due to the changes of dielectric.
Capacitor Microphone
Sound pressure varies the capacitance between a fixed plate and a movable diaphragm.
Magnetic Circuit Breaker
Inductance
Variation of self or mutual inductance of an AC excited coil by changes in the magnetic circuit.
Reluctance Pickup
Reluctance of the magnetic circuits is varied by changing the position of the iron core of the coil.

26. Contents Definition of Transducer Type of Transducers
Electrical Transducers
Parameters
Advantage/Disadvantages
Classification
Application
Selection of Transducers
Principle & Example of Transducers

27. Typical Application of Transducers
Pressure
Displacement
Force
Torque
Temperature
Sound
Power
Current
Magnetic Flux
Vibration
Velocity
Light
Position
Humidity
etc.

28. Contents Definition of Transducer Type of Transducers
Electrical Transducers
Parameters
Advantage/Disadvantages
Classification
Application
Selection of Transducers
Principle & Example of Transducers

29. Selection of Transducers
Operating Range
Range of transducer must be large enough to cover all expected magnitudes of the measurand.
Sensitivity
Provide sufficient output signal per unit change of measured input.
Errors (accuracy)
Should be as minima as possible to boost accuracy.

30. Selection of Transducers
Electrical Output Characteristics
Compatibility of output impedance, frequency response and the response time of the transducer output signal with the recording devices or measurement system.
Physical Environments
Transducer selected should be able to endure the environmental conditions.
Repeatability and Stability
Able to reproduce exact output signal when same measurand is applied.

31. ELECTRONIC INSTRUMENTATION
EKT 314/4
WEEK 3 : CHAPTER 2
END