Thermometer, Filled-System

Thermometer, Filled-System


a device for temperature measurement.

The operation of a filled-system thermometer is based on one of three principles: the thermal expansion of a liquid, the temperature dependence of the pressure of a gas, or the temperature dependence of the saturated vapor pressure of a liquid. A distinction is made between gas-filled, liquid-filled, and vapor-filled, or vapor-pressure, thermometers. (The substances that are used as fills in the three types are nitrogen, mercury, and ethyl chloride, respectively.)

A filled-system thermometer is a hermetically sealed system consisting of a bulb connected by a capillary to a readout or recording spring manometer. Thermometers of this type are commonly used in industry in the temperature range from –60° to 550°C. With long capillaries of up to 60 m such thermometers may be used for remote temperature measurement.

The scale of the manometer that measures the pressure in the bulb of a filled-system manometer is calibrated in degrees Celsius.