Again and again, we are asked the question concerning the difference between a complete pressure measurement and a gauge pressure measurement. To answer this question it helps to look at the definition of gauge pressure and absolute pressure. The difference between your two measurements is then explained relatively simply and thus also the choice of the appropriate measurement.
Definition of absolute pressure
Absolute pressure is really a pressure that is relative to the zero pressure in the empty, air-free space of the universe. This reference pressure may be the ideal or absolute vacuum. It is denoted with the subscript ?abs?: Pabs.
Definition of gauge pressure
The gauge pressure means the difference between a complete pressure (Pabs) and the prevailing atmospheric pressure (Pamb). It is denoted with the subscript ?e?: Pe and is calculated the following: Pe = Pabs ? Pamb.
Absolute vs gauge pressure measurement
The difference between the two measurements is relatively easily clarified: in a gauge pressure measurement, it will always be the difference from the existing ambient pressure that’s measured. However, this pressure changes with the weather and the height above sea level. An absolute pressure measurement measures the difference from the perfect or absolute vacuum. This is the reason this measurement is independent of environmental influences such as for example weather or altitude. Which Worthwhile is now the right one?
In practice, both measurements can be differentiated as follows: in many instances, the measuring task would be to determine the gauge pressure. Failure is exactly why this sort of sensor is most widely used. However, in case a gauge pressure sensor is used in an application in which the actual measuring task would be to gauge the absolute pressure, the following additional errors must be expected:
+/- 30 mbar caused by changes in weather
around 200 mbar when changing the location (e.g. from sea level to 2,000 m)
Depending on measuring range, these errors could be substantial (e.g. in pneumatics at a measuring selection of 1 bar) or negligible (in hydraulics at 400 bar).
Note
For anyone who is uncertain whether your measuring task needs a complete pressure or gauge pressure measurement, simply contact us ? we?ll be glad to work with you.