We have four
common temperature sensors used in industrial instrumentation.
Resistance Temperature Detector (RTD)
RTD responds
to heat by increasing its resistance to electric current.
Thermistor
This is
similar to RTD, except that its resistance decreases as it is heated.
Note that, in
both the RTD and Thermistor temperature sensors, the current variation due to
temperature change is usually very small. Current through an RTD or Thermistor
must be compared to current through another circuit containing identical
devices at a reference temperature to detect the change. The freezing
temperature of water is used as the reference temperature.
Semiconductor integrated circuit
This type of
temperature sensors respond to temperature increases by increasing reverse-bias
current across P-N junctions, generating a small but detectable current or
voltage proportional to temperature. The integrated circuit may contain its own
amplifier.
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Thermocouple
Thermocouple
type temperature sensors generate a small voltage proportional to the
temperature at the location where dissimilar metals are joined.
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