Transcript electronic instrumentation

ELECTRONIC INSTRUMENTATION
EKT 314/4
WEEK 3 : CHAPTER 2
TRANSDUCERS
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?
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.
Contents
 Definition of Transducer
 Type of Transducers
 Electrical Transducers
 Parameters
 Advantage/Disadvantages
 Classification
 Application
 Selection of Transducers
 Principle & Example of Transducers
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.
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
Contents
 Definition of Transducer
 Type of Transducers
 Electrical Transducers
 Parameters
 Advantage/Disadvantages
 Classification
 Application
 Selection of Transducers
 Principle & Example of Transducers
Type of Transducer
 Mechanical Transducers
 Electrical Transducers
Type of Transducer
 Mechanical 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
Contents
 Definition of Transducer
 Type of Transducers
 Electrical Transducers
 Parameters
 Advantage/Disadvantages
 Classification
 Application
 Selection of Transducers
 Principle & Example of Transducers
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.
Contents
 Definition of Transducer
 Type of Transducers
 Electrical Transducers
 Parameters
 Advantage/Disadvantages
 Classification
 Application
 Selection of Transducers
 Principle & Example of Transducers
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.
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
Contents
 Definition of Transducer
 Type of Transducers
 Electrical Transducers
 Parameters
 Advantage/Disadvantages
 Classification
 Application
 Selection of Transducers
 Principle & Example of Transducers
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.
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.
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).
Contents
 Definition of Transducer
 Type of Transducers
 Electrical Transducers
 Parameters
 Advantage/Disadvantages
 Classification
 Application
 Selection of Transducers
 Principle & Example of Transducers
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.
Transducer Classification
Active
Passive

Thermoelectric

Resistive

Piezoelectric

Inductive

Photovoltaic

Capacitive

Photoconductive

Piezoresistive

Magnetostrictive

Magnetoresistive

Electrokinetic

Thermoresistive

Electrodynamic

Elastroresistive

Electromagnetic

Hall Effect

Pyroelectric

Synchro

Galvanic

Gyro

Radio-active absorption

Ionic Conduction
Active Transducers
Type of
Transducers
Electrical
Principle of Operation
Parameters
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 and
Current
Voltage is generated across semiconductors
junction device when radiant energy stimulated
the cell.
Piezoelectric
Pickup
Voltage and
Current
EMF is generated when external force is applied
to certain crystalline materials, such as quartz.
Moving Coil
Generator
Voltage and
Current
Voltage is generated from the moving of coil in
magnetic field.
Passive Transducers
Type of
Transducers
Electrical
Principle of Operation
Parameters
Photomultiplier
Tube
Voltage and
Current
Secondary electron emission due to incident
radiation on photosensitive cathode.
Photoemissive Cell
Voltage and
Current
Electron emission due to the incident radiation
upon photo emissive surface.
Hall Effect Pickup
Voltage and
Current
Potential difference generated across a
semiconductor plate when magnetic flux
interacts with the applied current.
Ionisation Chamber
Voltage and
Current
Electron flow induced by ionization of gas due
to the radioactive radiation.
Passive Transducers (cont.)
Type of
Transducers
Electrical
Principle of Operation
Parameters
Potentiometer
Resistance
Variation of resistance in a potentiometer or
bridge circuit due to the positioning of the slider
by and external force.
Thermistor
Resistance
Resistance of certain metal oxide with negative
temperature coefficient of resistance varies with
temperature.
Photoconductive
Cell
Resistance
Variation of resistance of a cell as a circuit
element with incident of light.
Resistance
Hygrometer
Resistance
Variation of resistance of a conductive strip with
moisture content.
Passive Transducers (cont.)
Type of Transducers
Electrical
Principle of Operation
parameters
Dielectric Gauge
Capacitance
Variation of capacitance due to the
changes of dielectric.
Capacitor Microphone
Capacitance
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
Inductance
Reluctance of the magnetic circuits is
varied by changing the position of the iron
core of the coil.
Contents
 Definition of Transducer
 Type of Transducers
 Electrical Transducers
 Parameters
 Advantage/Disadvantages
 Classification
 Application
 Selection of Transducers
 Principle & Example of Transducers
Typical Application of Transducers
 Pressure
 Magnetic Flux
 Displacement
 Vibration
 Force
 Velocity
 Torque
 Light
 Temperature
 Position
 Sound
 Humidity
 Power
 etc.
 Current
Contents
 Definition of Transducer
 Type of Transducers
 Electrical Transducers
 Parameters
 Advantage/Disadvantages
 Classification
 Application
 Selection of Transducers
 Principle & Example of Transducers
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.
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.
ELECTRONIC INSTRUMENTATION
EKT 314/4
WEEK 3 : CHAPTER 2
END