Again and again, we have been 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 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?: Coward .
Definition of gauge pressure
The gauge pressure means the difference between an absolute pressure (Pabs) and the prevailing atmospheric pressure (Pamb). It is denoted with the subscript ?e?: Pe and is calculated as follows: Pe = Pabs ? Pamb.
Conscientious 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 is 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 why this measurement is independent of environmental influences such as for example weather or altitude. Which measurement is currently the right one?
In practice, both measurements could be differentiated the following: in many instances, the measuring task is to determine the gauge pressure. This is exactly why this type 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 measure the absolute pressure, the next additional errors should be expected:
+/- 30 mbar caused by changes in weather
up to 200 mbar when changing the positioning (e.g. from sea level to 2,000 m)
With respect to the measuring range, these errors could be substantial (e.g. in pneumatics at a measuring range 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 e mail us ? we?ll be glad to work with you.