Module II Transducers
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Transcript of Module II Transducers
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Module II
Transducers
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Transducers
An electronics instrumentation system consists of a number ofcomponents to perform a measurement and record its result.
A measurement system consist of three major components
1. An input devices,
2. A signal conditioning or processing device,
3. An output devices.
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Transducer: a device which converts one form ofenergy to another
Sensor: a transducer that converts a physicalphenomenon into an electric signal. an interface between the physical world and the computing
world.
Actuator: a transducer that convertselectric signal to a physical
phenomenon
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Contd
Transducer
Transducers as which, when actuated transforms energy
from one form to another. A device which convert a physically parameter such as heat ,
intensity of light , flow rate , liquid level, humidity and pH
value into electrical form by means of transducers.
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These transducers provide an output signal when stimulated
by a mechanical or non-mechanical input
A photoconductor convert light intensity into change of
resistance A thermocouple convert heat energy into electrical voltage
A force produces a change of resistance in strain gauge
An acceleration produces a voltage in a piezo-electrical
crystal and so on.
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Electrical transducers
In electrical system to measure non-electrical quantities a
detector is used which usually convert the physical quantity
into displacement , this displacement actuates an electrical
transducer, gives an output that is electrical in nature. The electrical signal may be a current be a current or a voltage
or a frequency and production of these signals is based upon
electrical effects
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Advantage ofElectrical transducers
Electrical amplification and attenuation can be done easily
The mass-inertia effects are minimized
The effects of friction are minimized
The electrical system very less power
Telemetry is used in almost all sophisticated measurement
systems
Miniaturization on account of use ofICs
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Note:
1. The reason for transforming a physical phenomenon into
electrical form is that the electrical output can be easily used,
transmitted and processed for purpose of measurement.
2. Another name of transducer is pick up.
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The transducer may be consist two part
1. Sensing or detector element: It is that part oftransducer which respond to a physical phenomenon or
change in a physical phenomenon.
2. Transduction element : A transduction elementtransforms the output of a sensing element to an electrical
output. The transduction element , in a way acts as a
Secondary transducer
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Classification oftransducers
The transducers can be classified
(i) On the basis of transduction form used,
(ii) as primary and secondary transducers,
(iii) as passive and active transducers,
(iv) as analog and digital transducers and
(v) as transducers and inverse transducers
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(1) Classification based upon principal of Transduction: Basis
of principal of transduction as resistive, inductive,
capacitive.
Example: piezoelectric, thermoelectric, potentiometer devices,photoconductive cell etc.
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(ii) Primary and secondary transducer:
Example: Convert pressure into displacement by help of
Bourdon's tube and linear variable differential transformer
(iii) Passive and active
Example :resistive, inductive and capacitive transducers
( Passive)
Example: Thermocouples, photovoltaic cells etc( Active)
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(iv) Analog transducers: Convert input quantity into analog
output
Example: Thermocouple, thermistor, strain gauge, LVDT etc.
Digital Transducer: convert input quantity into electrical pulse
(v) Inverse transducers: Convert an electrical quantity into non-
electrical
Example: Oscilloscopes, Convert electrical signal intomechanical movement
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Selection ofatransducers
The following factor should be considered while selecting a
transducer:
1. Operating range : Chosen to maintain range requirements
and good resolution2. Sensitivity: The transducer must be sensitivity enough to
produce detectable output.
3. Accuracy:
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Types of transducer based on principal
Resistive transducers
Capacitive transducers
Variable inductance transducers
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Resistive Transducer
Resistive transducers are those in which resistance the
resistance changes due to a change in some physical
phenomenon.
The change in the value of the resistance with a change in thelength of the conductor can be used to measure displacement.
strain gauge used for measurement of displacement, force and
pressure. Its work on the principal that the resistance of a
conductor or semiconductor change when strained.
The resistive of materials change with change in temperature.
This property can be used for the measurement of temperature.
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Contd
Resistive transducer:
Potentiometer
Strain gauge
Rosettes
Thermistors
RTD ( Resistance Temperature Detector)
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Capacitive transducers
Measurement of liquid level by change in variationof dielectric constant
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Inductance Transducers
Self Generating type and passive type
Piezoelectric Transducers
Photoelectric transducers
Digital transducer
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Potentiometer
A resistive potentiometer (pot) consists of a resistanceelement provided with a sliding contact, called a wipe.
The motion of the sliding contact may be translatory or
rotational. The potentiometer is a passive transducer
since it requires an external power source for its operation
Note : On the basis of motion these are three types
(i) Translatory Type (ii) Rotation Type (iii) Helipot
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Advantage of potentiometer
They are inexpensive Simply to operate
They are useful fore the measurement of large amplitudes of
displacement.
Electric efficiency is very high, and they provide sufficient
output to allow control operation.
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Disadvantages
When using linear potentiometer, a large force is required tomove the sliding contact
The sliding contact can wear out, become misaligned and
generate noise.
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Numerical
A displacement transducer with a shaft stroke of 4.0 inch isapplied to the circuit. The total resistance of the potentiometer
is 5Kohm. The applied voltage Vt is 5V. When the wiper is 1.2
inch from B, What is the value of the output voltage?
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Solution
R2= (1.2 inch/4.0 inch) * 5 K= 1500 ohm
Then Vo= Vt* / R2+R1=5V*15000hm/5K=1.5
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Strain Gauge
Strain
Definition: Strain is the definition of how much a material has
been stretched (or compressed) when compared to its original
length. The most common measure of strain in metals is calledengineering strain, calculated as the change in length divided
by the original length. For example, a 2.0" titanium bar that
has been stretched to 2.2" is said to have experienced a tensile
strain of 0.1, or 10%.
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Types ofstarin
Linear Strain
Lateral Strain
Volumetric Strain Shear Strain
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Contd
Strains
Strain is defined a the ratio of change in dimension to original
dimension of a body when it is deformed. It is a dimensionless
quantity as it is a ratio between two quantities of samedimension.