Page 901 - Basic Electrical Engineering

1. Potentiometric force or pressure, resistance, and hence Measurement of force,
output voltage gets changed. pressure, displacement

Resistance of a wire or a
semiconductor gets changed due to Stress, pressure, force,
2. Strain gauge
stress developed on the surface on torque, displacement
which the gauge is pasted/fixed.
Temperature rise changes the
resistance. Resistance of certain
Temperature, thermal
3. Thermistor materials decrease with increase in conductivity
temperature. Resistance change is a
measure of temperature.
Potential difference is attained across a
4. Hall effect transducer or Magnetic flux, current,
material carrying current in a
pick-up velocity
transverse magnetic field.
When the position of the magnetic core
is changed, the differential voltage of
5. Linear variable Measurement of
differential transformer two secondary windings of a displacement, force,
transformer is changed. Output voltage
(LVDT) pressure, position
is proportional to the position of the
core, i.e., its displacement.

Variation of distance between the two
plates, area of overlap, changing, the
position of the dielectric material
Displacement, force,
6. Capacitive transducer between the plates changes the pressure,
capacitance. Change in capacitance is
converted into an electrical signal by
using a bridge circuit.

By moving the core material inside the
coil its self-inductance is changed.
7. Inductive transducer Mutual inductance between two coils is Pressure, displacement
changed by varying the magnetic
circuit.

(B) Active transducers
Conversion principle Typical applications
requiring no power supply
EMF is induced when junctions of
certain dissimilar materials are heated
1. Thermocouple
transducer at different temperatures. One junction Temperature, heat flow
is taken as reference junction of known
temperature.

When force is applied on certain
2. Piezoelectric transducer material such as quatz, EMF is induced Pressure, force, vibrations
between the two sides.