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

Diaphragm pressure gauges are believed as specialists in the process industries. They come into play when Bourdon tube pressure gauges reach the limits of these performance. One of the benefits of diaphragm pressure gauges is the measurement of low pressures.
Diaphragm pressure gauges can 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 only 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 larger 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 ? 250 mbar 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 have to be exceptionally thin to experience 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 contain two diaphragms welded together, which can be loaded with pressure from the within. This results in a double diaphragm travel. In this manner, even the cheapest of pressures could be measured without reducing the wall thickness. However, because the pressure chamber is not self-draining, capsule elements are not ideal for applications with liquid media.
Note
Frantic 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 Provocative of diaphragm pressure gauges (2): High overload protection

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