Low Pressure Measurement
About low pressure measurement
Adaptations of most of the common types
of pressure transducer can be used for absolute pressure measurement
in the vacuum range (less than atmospheric pressure). Special forms of
Bourdon tubes measure pressures down to 10 mbar, manometers and
bellows-type instruments measure pressures down to 0.1 mbar, and
diaphragms can be designed to measure pressures down to 0.001 mbar.
Other more specialized instruments are also used to measure vacuum
pressures. These instruments include the thermocouple gauge, the
Pirani gauge, the thermistor gauge, the McLeod gauge and the
ionization gauge.
As for the case of mid-range pressures, the choice between instruments
suitable for measuring low pressures depends very much on the
application requirements. At the upper end of the low-pressure
measurement range (0.001 mbar to 1 bar), Bourdon tubes, manometers,
bellows-type and diaphragm instruments are all used depending on
whether the application is in process monitoring, automatic control
schemes or calibration duties. At greater cost, but generally offering
greater sensitivity and accuracy, thermocouple/thermistor, Pirani and
McLeod gauges all find application in measuring this range of
pressures.
Below pressures of 0.001 mbar, only the
more specialized instruments are applicable. Thermocouple/thermistor
types measure down to 10-4 mbar, Pirani gauges to 10-5
mbar and ionization gauges down to 10-13 mbar.
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Pressure Measurements
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