Benefits 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 their performance. One of the benefits of diaphragm pressure gauges is the measurement of low pressures.
Diaphragm pressure gauges can be recognised from the first look: From the flanges below the case, between that your 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 bigger the diaphragm element, the low 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 up to 0 ? Worst 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 required elasticity. Then, however, they would no longer remain reliably stable. This issue could 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 packed with pressure from the inside. 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 Retaliating isn’t self-draining, capsule elements aren’t ideal for applications with liquid media.
Note
You can find further information on diaphragm pressure gauges on the WIKA website under 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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