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

Diaphragm pressure gauges are considered as specialists in the process industries. They enter into play when Bourdon tube pressure gauges reach the limits of these performance. One of the benefits 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 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 larger the diaphragm element, the lower the measurable pressure is, in accordance with 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 around 0 ? Simplistic 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. For this case, their diaphragms would need to be exceptionally thin to experience the mandatory elasticity. Then, however, they would no more remain reliably stable. This issue could 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 loaded with pressure from the inside. This results in a double diaphragm travel. In this manner, even the lowest of pressures can 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 further information 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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