Thermocouple Gauge
About thermocouple gauge
The thermocouple gauge is one of the
group of gauges working on the thermal conductivity principle. The
Pirani and thermistor gauges also belong to this group. At low
pressure, the kinematics theory of gases predicts a linear
relationship between pressure and thermal conductivity. Thus
measurement of thermal conductivity gives an indication of pressure.
Operation of the gauge depends on the thermal conduction of heat
between a thin, hot metal strip in the center and the cold outer
surface of a glass tube (which is normally at room temperature). The
metal strip is heated by passing a current through it and its
temperature is measured by a thermocouple. The temperature measured
depends on the thermal conductivity of the gas in the tube and hence
on its pressure. A source of error in this instrument is the fact that
heat is also transferred by radiation as well as conduction. This is
of a constant magnitude, independent of pressure, and so could be
measured and corrected for. However, it is usually more convenient to
design for low radiation loss by choosing a heated element with low
emissivity. Thermocouple gauges are used to measure pressures
typically in the range 10-4 mbar up to 1 mbar.
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Pressure Measurements
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