Liquid-in-Glass Thermometers
About liquid-in-glass thermometers
Thermal expansion methods make use of
the fact that the dimensions of all substances, whether solids,
liquids or gases, change with temperature. Instruments operating on
this physical principle include the liquid-in-glass thermometer, the
bimetallic thermometer and the pressure thermometer.
Liquid-in-glass thermometers
The liquid-in-glass thermometer is a well-known temperature measuring
instrument which is used in a wide range of applications. The fluid
used is usually either mercury or colored alcohol, and this is
contained within a bulb and capillary tube. As the temperature rises,
the fluid expands along the capillary tube and the meniscus level is
read against a calibrated scale etched on the tube. The process of
estimating the position of the curved meniscus of the fluid against
the scale introduces some error into the measurement process and a
measurement accuracy better than ±1% of full-scale reading is hard to
achieve.
However, an accuracy of ±0.15% can be obtained in the best industrial
instruments. Industrial versions of the liquid-in-glass thermometer
are normally used to measure temperature in the range between -200 °C
and +1000 °C, although instruments are available to special order
which can measure temperatures up to 1500 °C.
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Temperature Measurements
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