Temperature Transducers

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.