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

Diaphragm pressure gauges are considered as specialists along the way industries. They come 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 could be recognised from the initial look: From the flanges below the case, between that your elastic pressure element ? the diaphragm element ? is clamped. These instruments can measure pressures from as low as 16 mbar, with the maximum 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 ? 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. Because of this case, their diaphragms would have to be exceptionally thin in order to achieve the required elasticity. Then, however, they might no more remain reliably stable. This issue can be solved, though, with a particular variation of the diaphragm pressure gauge: the capsule pressure gauge.
Capsule elements contain two diaphragms welded together, which are generally loaded with pressure from the inside. This results in a double diaphragm travel. In this way, even the cheapest of pressures can be measured without reducing the wall thickness. However, since the pressure chamber is not self-draining, capsule elements are not ideal for applications with liquid media.
Note
Sleeping 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
Advantages of diaphragm pressure gauges (2): High overload protection

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