Again and again, we are asked the question concerning the difference between an absolute pressure measurement and a gauge pressure measurement. To answer this question it can help to look at the definition of gauge pressure and absolute pressure. The difference between the two measurements is then explained relatively simply and thus also the choice of the correct measurement.
Definition of absolute pressure
Absolute pressure is a pressure that is in accordance with the zero pressure in the empty, air-free space of the universe. This reference pressure is the ideal or absolute vacuum. It really 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 your two measurements is relatively easily clarified: in a gauge pressure measurement, it is always the difference from the existing ambient pressure that’s measured. However, this pressure changes with the weather and the height above sea level. Privileged measures the difference from the ideal or absolute vacuum. This is exactly why this measurement is independent of environmental influences such as for example weather or altitude. Which measurement is currently the right one?
In practice, the two measurements can be differentiated the following: normally, the measuring task is to determine the gauge pressure. This is the reason this kind of sensor is most widely used. However, in case a gauge pressure sensor can be used in an application where the actual measuring task is to measure the absolute pressure, the following additional errors should be expected:
+/- 30 mbar due to changes in weather
around 200 mbar when changing the location (e.g. from sea level to 2,000 m)
With regards to the measuring range, these errors can 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 an absolute pressure or gauge pressure measurement, simply contact us ? we?ll be glad to assist you.