Again and again, we have been asked the question about 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 your two measurements is then explained relatively simply and therefore 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 may be the ideal or absolute vacuum. It really is denoted with the subscript ?abs?: Pabs.
Definition of gauge pressure
The gauge pressure is defined as the difference between a complete pressure (Pabs) and the prevailing atmospheric pressure (Pamb). Great is denoted with the subscript ?e?: Pe and is calculated as follows: Pe = Pabs ? Pamb.
Festive 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 elements and the height above sea level. A complete pressure measurement measures the difference from the ideal or absolute vacuum. That is why this measurement is independent of environmental influences such as for example weather or altitude. Which measurement is now the right one?
In practice, both measurements can be differentiated as follows: in most cases, the measuring task is to determine the gauge pressure. This is why this sort of sensor is most widely used. However, if a gauge pressure sensor is used in an application where the actual measuring task would be to measure the absolute pressure, the following additional errors must be expected:
+/- 30 mbar caused by changes in weather
around 200 mbar when changing the positioning (e.g. from sea level to 2,000 m)
Depending on 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
When you are uncertain whether your measuring task needs a complete pressure or gauge pressure measurement, simply e mail us ? we?ll be glad to work with you.