Transducers Short notes | Sensor & Industrial Instrumentation - Electronics and Communication Engineering (ECE) PDF Download

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Transducers
Transducers are devices that convert one form of energy into another, widely used in sensors
and industrial instrumentation to measure physical quantities. This section covers their types,
characteristics,andapplications.
1. De?nitionandClassi?cation
Atransducerconvertsaphysicalquantity(e.g.,temperature,pressure)intoameasurablesignal
(e.g.,voltage,current).
• Classi?cationbyEnergyConversion:
– Active Transducers: Generate output without external power (e.g., piezoelectric,
thermocouple).
– PassiveTransducers: Requireexternalpower(e.g.,resistive,capacitive,inductive).
• Classi?cationbyOutputSignal:
– AnalogTransducers: Continuousoutput(e.g.,thermistor).
– DigitalTransducers: Discreteoutput(e.g.,opticalencoders).
2. KeyCharacteristics
Transducerperformanceisevaluatedbasedonthefollowingparameters:
• Sensitivity: Output change per unit input change, S =
?Output
?Input
. E.g., for a strain gauge,
S =
?R/R
?
,where?isstrain.
• Linearity: Degree to which output is proportional to input. Nonlinearity error: e =
ActualOutput-IdealOutput
Full-ScaleOutput
.
• Range: Minimumtomaximummeasurableinputvalues.
• Resolution: Smallestdetectableinputchange.
• Accuracy: Closenessofoutputtotruevalue,oftenexpressedaspercentageerror.
3. CommonTransducers
• ResistiveTransducers:
– StrainGauge: Resistancechangeswithstrain,
?R
R
=GF·?,whereGF isthegauge
factor.
– Thermistor: Resistance varies with temperature, typically R
T
= R
0
e
ß
(
1
T
-
1
T
0
)
,
whereß isamaterialconstant.
• CapacitiveTransducers: Capacitance changes with displacement,C =
?
0
?rA
d
, where?
0
ispermittivityoffreespace,?
r
isrelativepermittivity,Aisplatearea,anddisseparation.
• Inductive Transducers: Inductance varies with position (e.g., LVDT), output voltage
V
out
??x,where?xiscoredisplacement.
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Page 2


Transducers
Transducers are devices that convert one form of energy into another, widely used in sensors
and industrial instrumentation to measure physical quantities. This section covers their types,
characteristics,andapplications.
1. De?nitionandClassi?cation
Atransducerconvertsaphysicalquantity(e.g.,temperature,pressure)intoameasurablesignal
(e.g.,voltage,current).
• Classi?cationbyEnergyConversion:
– Active Transducers: Generate output without external power (e.g., piezoelectric,
thermocouple).
– PassiveTransducers: Requireexternalpower(e.g.,resistive,capacitive,inductive).
• Classi?cationbyOutputSignal:
– AnalogTransducers: Continuousoutput(e.g.,thermistor).
– DigitalTransducers: Discreteoutput(e.g.,opticalencoders).
2. KeyCharacteristics
Transducerperformanceisevaluatedbasedonthefollowingparameters:
• Sensitivity: Output change per unit input change, S =
?Output
?Input
. E.g., for a strain gauge,
S =
?R/R
?
,where?isstrain.
• Linearity: Degree to which output is proportional to input. Nonlinearity error: e =
ActualOutput-IdealOutput
Full-ScaleOutput
.
• Range: Minimumtomaximummeasurableinputvalues.
• Resolution: Smallestdetectableinputchange.
• Accuracy: Closenessofoutputtotruevalue,oftenexpressedaspercentageerror.
3. CommonTransducers
• ResistiveTransducers:
– StrainGauge: Resistancechangeswithstrain,
?R
R
=GF·?,whereGF isthegauge
factor.
– Thermistor: Resistance varies with temperature, typically R
T
= R
0
e
ß
(
1
T
-
1
T
0
)
,
whereß isamaterialconstant.
• CapacitiveTransducers: Capacitance changes with displacement,C =
?
0
?rA
d
, where?
0
ispermittivityoffreespace,?
r
isrelativepermittivity,Aisplatearea,anddisseparation.
• Inductive Transducers: Inductance varies with position (e.g., LVDT), output voltage
V
out
??x,where?xiscoredisplacement.
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• Piezoelectric Transducers: Generate voltage proportional to mechanical stress, V =
g·t·s,whereg isthepiezoelectricconstant,tisthickness,ands isstress.
• Thermocouple: Voltage generated due to temperature difference, V = a(T
1
- T
2
),
wherea istheSeebeckcoef?cient.
4. Applications
• Industrial: Pressuresensorsinprocesscontrol,LVDTsforpositionmeasurement.
• Medical: Ultrasoundtransducers,temperaturesensors.
• Automotive: Accelerometersforairbagsystems,straingaugesforstructuralmonitoring.
• Environmental: Thermocouples for temperature monitoring, capacitive sensors for hu-
midity.
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