Expansion thermometer - alternative to gas-actuated thermometer

By T Jung and C Ball, WIKA


Published in:

Electricity+Control March 2014 (pages 48-49)

Enquiries: WIKA South Africa, www.wika.co.za


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The most frequently recognised methods of temperature measurement are the bimetallic thermometer, the gas-actuated thermometer and the liquid-expansion thermometer, commonly referred to as an expansion thermometer.

A liquid expansion thermometer, or expansion thermometer, works much like a gas-actuated thermometer. The difference lies in the fact that an expansion thermometer is not filled with gas, but rather with a thermometric liquid. Just like the gas, the liquid also expands as the temperature rises and thus causes the pressure in the system to rise. Furthermore, the expansion thermometer does not require a movement to convert the tube deflection into a rotational motion.

With expansion thermometers, instead of a C-shaped Bourdon tube, a helically wound Bourdon tube is used. Through the winding, an expansion of the tube results in a rotational motion. The pointer shaft of the expansion thermometer is connected directly with the tube. If the temperature at the probe rises, the liquid expands and increases the pressure in the system. The tube bends out and thus leads to a rotary motion. The pointer connected to the tube moves in proportion to the temperature change.

By dispensing with the movement and using a liquid as the filling medium, an expansion thermometer can be manufactured considerably more cost-effectively than a gas-actuated thermometer.

Gas-actuated thermometers and expansion thermometers are used in industrial applications for the reliable measurement of temperature in processes, machinery and plants. What many users do not know, however, is that expansion thermometers with stainless steel cases and accuracy class 1 can be used as an alternative to gas-actuated thermometers.


Take note:

  • Expansion thermometers are used in industrial applications for the reliable measurement of temperature.
  • Expansion thermometers can be used as alternatives to gas-actuated thermometers.
  • Expansion thermometers can be manufactured cost-effectively.