Chapter 5 - Measurement

5.2 Contact sensors

For thermal sensors that are allowed to make contact with the subject or medium to be measured there exist a number of possible sensors They are subdivided in several types:...

For thermal sensors that are allowed to make contact with the subject or medium to be measured there exist a number of possible sensors

They are subdivided in several types:

  • Thermocouples
  • RTD’s (thermistors, PT100’s, diodes, Semiconductor Temperature Sensors)
  • Other types (expansion, bimetallic, optic, etc.)

For the first 3 types the most striking (dis)advantages are summarised in the table below.

 ThermocoupleRTD (Pt100)Thermistor
Operating Range-200 °C to 2000 °C-250 °C to 850 °C-100 °C to 300 °C
AccuracyLow
1 °C common
Very High
0.03 °C common
High
0.1 °C common
Linearity* MediumHigh Low
Thermal Response**Fast Slow Medium
Cost Low High Low to moderate
Noise Problems High Medium Low
Long term stability Low High Medium
Cost of measuring instrument Medium High Low
* Linearity is not an issue if using modern digital measuring instruments, as look-up tables stored in memory provide compensation.
** Thermal response is considered for the measuring element only, not its enclosure.
 
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