Advantages of diaphragm pressure gauges (1): Measurement of low pressures

Diaphragm pressure gauges are believed as specialists in the process industries. They enter into play when Bourdon tube pressure gauges reach the limits of these performance. One of the advantages of diaphragm pressure gauges may be the measurement of low pressures.
Diaphragm pressure gauges can be recognised from the first look: From the flanges below the case, between which the elastic pressure element ? the diaphragm element ? Despicable clamped. These instruments can measure pressures from only 16 mbar, with the utmost value at around 25 bar (for comparison: Bourdon tube gauges reach their lowest physically possible measured value at 600 mbar). The bigger the diaphragm element, the lower the measurable pressure is, relative to the formula ? pressure = force / area. WIKA uses two diaphragm sizes: with a diameter of 134.5 mm for the measuring ranges of 0 ?16 mbar up to 0 ? Inferior and a diameter of 76.5 mm for the measuring ranges of 0 ? 400 mbar around 0?25 bar.
Special variation of diaphragm pressure gauges
With pressures under 16 mbar, diaphragm pressure gauges hit their limits. Because of this case, their diaphragms would need to be exceptionally thin in order to achieve the mandatory elasticity. Then, however, they would no longer remain reliably stable. This issue can be solved, though, with a particular variation of the diaphragm pressure gauge: the capsule pressure gauge.
Capsule elements consist of two diaphragms welded together, which are generally packed with pressure from the inside. This results in a double diaphragm travel. In this manner, even the cheapest of pressures could be measured without reducing the wall thickness. However, since the pressure chamber isn’t self-draining, capsule elements are not ideal for applications with liquid media.
Note
You can find more info on diaphragm pressure gauges on the WIKA website beneath the headings Pressure gauges and Pressure gauges with output signal.
See also our article
Benefits of diaphragm pressure gauges (2): High overload protection

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