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 helps to look at the definition of gauge pressure and absolute pressure. The difference between the two measurements is then explained relatively simply and therefore also the decision of the correct measurement.
Great 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 is 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 really 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 usually the difference from the current 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 ideal or absolute vacuum. This is the reason this measurement is independent of environmental influences such as for example weather or altitude. Which measurement is now the right one?
In practice, the two measurements can be differentiated the following: usually, the measuring task is to determine the gauge pressure. That is why this sort of sensor is most widely used. However, in case a gauge pressure sensor can be used in an application in which the actual measuring task is to measure the absolute pressure, the next additional errors must be expected:
+/- 30 mbar due to changes in weather
up to 200 mbar when changing the location (e.g. from sea level to 2,000 m)
Based on the measuring range, these errors can be substantial (e.g. in pneumatics at a measuring range of 1 bar) or negligible (in hydraulics at 400 bar).
Note
In case you are uncertain whether your measuring task needs a complete pressure or gauge pressure measurement, simply contact us ? we?ll be glad to assist you.