Biomedical Engineering Reference
In-Depth Information
Table 1.1
Typical examples of sensor elements
S.
no.
Input variable to transducer
Output
variable of
transducer
Principle of operation
Type of device
(sensor)
1
Temperature
Voltage
An e.m.f is generated across the junctions of two dissimilar metals or
semiconductors when that junction is heated
Thermocouple
2
Temperature
Displacement
There is a thermal expansion in volume when the temperature of liquids or
liquid metals is raised and this expansion can be shown as displacement of
the liquid in the capillary
Liquid in glass
thermometer
3
Temperature
Resistance
change
Resistance of pure metal wire with positive temperature coefficient varies with
temperature
Resistance
thermometer
4
Temperature
Pressure
The pressure of a gas or vapor varies with the change in temperature
Pressure thermometer
5
Displacement
Inductance
change
The differential voltage of the two secondary windings varies linearly with the
displacement of the magnetic core
Linear variable
differential
transducer (LVDT)
6
Displacement
Resistance
change
Positioning of a slider varies the resistance in a potentiometer or a bridge circuit
Potentiometric Device
7
Motion
Voltage
Relative motion of a coil with respect to a magnetic field generates a voltage
Electro dynamic
generator
8
Flow rate
Pressure
Differential pressure is generated between the main pipe line and throat of the
Venturi meter/Orifice meter
Venturi meter/orifice
meter
9
Flow velocity
Resistance
change
Resistance of a thin wire/film is varied by convective cooling in stream of gas/
liquid flows
Hot wire anemometer
(gas flows)
Hot film anemometer
(liquid flows)
10
Pressure
Movement of
liquid
column
The impressed pressure is balanced by the pressure generated by a column of
liquid
Manometer
11
Pressure
Displacement
The application of pressure causes displacement in elastic elements
Bourdon gage
12
Gas pressure
Resistance
change
Resistance of a heating element varies by convective cooling
Pirani gage
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