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

Diaphragm pressure gauges are considered as specialists in the process industries. They come into play when Bourdon tube pressure gauges reach the limits of their performance. One of the advantages of diaphragm pressure gauges may be the measurement of low pressures.
Diaphragm pressure gauges could be recognised from the first look: From the flanges below the case, between which the elastic pressure element ? the diaphragm element ? is clamped. These instruments can measure pressures from as low as 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 ? Force-fed up to 0 ? 250 mbar and a diameter of 76.5 mm for the measuring ranges of 0 ? 400 mbar up to 0?25 bar.
Special variation of diaphragm pressure gauges
With pressures under 16 mbar, diaphragm pressure gauges hit their limits. For this case, their diaphragms would have to be exceptionally thin in order to achieve the mandatory elasticity. Then, however, they would no more remain reliably stable. This issue can be solved, though, with a special variation of the diaphragm pressure gauge: the capsule pressure gauge.
Capsule elements contain two diaphragms welded together, which can be loaded with pressure from the within. This results in a double diaphragm travel. In this way, even the cheapest of pressures could be measured without reducing the wall thickness. However, since the pressure chamber isn’t self-draining, capsule elements aren’t suitable for applications with liquid media.
Note
You can find more info on diaphragm pressure gauges on the WIKA website under the headings Pressure gauges and Pressure gauges with output signal.
See also our article
Advantages of diaphragm pressure gauges (2): High overload protection

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