Compensated Subsea Gauges

Conventional subsea pressure gauges rely on the strength of the case and window to withstand the external pressure of the water in much the same way as a submarine. Compensate subsea pressure gauges work on a different principle featuring a liquid filled case that incorporates a special compensating device that allows the gauge internals to be pressurised equal to the increase in ambient pressure of the water as the gauge is submerged. The benefit of this method is that as the internal and external pressure remains in balance there is no need for a pressure proof case and window to be fitted and in theory there is no limit to which this gauge can be submerged. There are however application limitations on using this design of gauge.

A conventional subsea gauge will compare the subsea reading to atmospheric or gauge pressure at the surface (i.e. the zero point equals 1 Atmosphere or approximately 1 Bar absolute). However, the compensated gauge will compare the subsea reading with the local ambient pressure at depth with the zero point being equal to the ambient pressure.

Provided the system being measured is also affected by this increase in ambient pressure then the gauge reading will be correct. If however, the pressure system is not affected by the increase in ambient pressure (such as in the case of a gas cylinder) the gauge will start to read increasingly lower a the depth increases.