Resistance temperature Detector ( RTD) | Diagram and Advantages

RESISTANCE TEMPERATURE DETECTORS (RTDS)

When a metal wire is heated the resistance increases. So, a temperature can be measured using the resistance of a wire. RTD incorporates pure metals or certain alloys that increases resistance as temperature increases and it conversely decreases resistance as temperature decreases. RTDs act similar an electrical transducer.and it converts changes the temperature to voltage signals by the measurement of resistance.

The metals that are best suited for use as RTD sensors are pure of uniform quality and stable within to given range of temperature and able to give reproducible resistance- temperature readings. Only a few metals have the properties necessary for use in RTD elements. ,

RTD elements are normally constructed of platinum, copper, nickel or nickel-iron alloys.

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construction of a resistance temperature detector
construction of a resistance temperature detector

Figure 2.5.3 shows the construction of a RTD. It has a resistor element connected to a Wheatstone bridge. The element and the connection leads are insulated and protected by a sheath. A small amount of current is continuously passing though the coil. As the temperature changes the resistance of the coil changes which is detected at the Wheatstone bridge.

RTDs are used in the form of thin films,wire wound or coil. They are generally made of metals such as platinum, nickel or nickel-copper alloys. Platinum wire held by a high-temperature glass adhesive in a ceramic tube is used to measure the temperature in a metal furnace.

Other applications are:

  • Air conditioning and refrigeration servicing
  • Food Processing
  • Stoves and grills
  • Textile production
  • Plastics processing
  • Petrochemical processing
  • Micro electronics
  • Air, gas and liquid temperature measurement in pipes and tanks
  • Exhaust gas temperature measurement

Advantages of RTDs

  1. It is suitable for measuring high temperatures
  2. It has high degree of accuracy
  3. It ensures good stability and repeatability
  4. It does not need a reference temperature junction

Disadvantages of RTDs

  1. Size is more than the thermocouple
  2. Power supply is required
  3. It needs auxiliary apparatus to get required form of output
  4. Resistance element is more expensive than a thermocouple
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