Relative Pressure Gauges

Determination of the deformation of an elastic tube

Bourdon gaugePressure is the force, acting on unit area. In many cases, applying a force leads to a deformation of the object under study. The resulting deformation can be measured and is proportional to the applied force (Hooke's law). Hence, the deformation can be used to determine the pressure. This deformation is especially significant in the upper pressure range (up to atmospheric conditions).

In the simplest case (e.g. Bourdon gauge) the pressure deforms a metal ring and the resulting strain is directly displayed on a calibrated scale. In this type of gauges the pressure refers to the ambient barometric pressure (1000 mbar on display corresponds to ambient pressure). Therefore the measured values, if compared with absolute pressure, reveal high fluctuations.

Piezo-resistive diaphragm vacuum gauges -
Piezo-resistive determination of the deflection of an elastic membrane

Piezo-resistive diaphragm vacuum gauges can achieve higher accuracy than Bourdon gauges. They rely on similar principle as the capacitive diaphragm vacuum gauges: the pressure is derived from the mechanical deformation of a membrane measured with a piezo-resistive element. The specific resistivity of the piezoelement depends on the deflection of the membrane and, thus, it provides information about the pressure difference between both sides of the membrane. The accuracy of the pressure determination is typically around 0.5 % FS (full scale), i.e. reliable measurement range is about 3 decades.

Usually, piezo-resistive diaphragm vacuum gauges have a full scale deflection between 1300 and 1500 mbar. Long-term and temperature stability, as well as the resolution are slightly worse than the ones of capacitive diaphragm vacuum gauges. However, piezo-resistive diaphragm vacuum gauges are considerably cheaper.

 

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