Comparison between temperature measuring devices

instrumentation

#1

The four most common temperature transducers are thermocouples, resistance-temperature detector’s (RTD’s), thermistors, and integrated circuit sensors.

Here we are discussing about advantages and disadvantages of each devices

Thermocouple:

A thermocouple is an active transducer which directly converts thermal energy into electrical energy. It is a simple device made by joining to dissimilar metals or semiconductor forming a junction. It produces a voltage when the temperature at the junction changes. Have a temperature range in different types -300 to 3200°F

Chara & symbol:

Advantages:

  • Self-powered
  • Simple
  • Rugged
  • Inexpensive
  • Wide variety of physical forms
  • Wide temperature range

Disadvantages:

  • Non-linear
  • Low voltage
  • Reference required
  • Least stable
  • Least sensitive
  • Complicated conversion from emf to temperature

RTD:

RTD (Resistance Temperature Detectors) uses metals that change their resistance when exposed to temperature, which has a positive temperature coefficient. For PT100 RTD it has a temperature range from -400 to 1200F.

Chara & symbol:

Advantages:

  • Most stable
  • Most accurate
  • More linear than thermocouple.
  • Interchangeability over wide range
  • Works in wide temperature ranges

Disadvantages:

  • Bulky in size and fragile
  • Expensive
  • Slow
  • Current source required
  • Small resistance change
  • Four-wire measurement
  • Self-heating problems

Thermistor:

Thermistors are semiconductor devices which have a negative temperature coefficient, this means that the resistance decreases with an increase in temperature.

Thermistors are available that perform temperature measurement from -73 to 316°C (-100 to 600°F). It should be noted that many have limited ranges and cannot be used above 120°C (250°F).

Chara & symbol:

Advantages:

  • High output
  • Fast
  • Two-wire ohmic measurement
  • Very high sensitivity (Select range)
  • Inexpensive
  • No cold junction compensation

Disadvantages:

  • Not easily interchangeable
  • Limited temperature range
  • Fragile
  • Current source required
  • Self-heating
  • Narrow span
  • Unstable due to drift and decalibration (especially at high temperatures)

I.C sensor:

They are semiconductor devices. These are available in both voltage and current-output configurations, Some integrated sensors even represent temperature in a digital output format that can be read directly by a microprocessor.

Chara & symbol:

Advantages:

  • Most linear
  • Highest output
  • Inexpensive

Disadvantages:

  • T < 250°C
  • Power supply required
  • Self-heating
  • Limited configurations