Again and again, we are asked the question about the difference between an absolute pressure measurement and a gauge pressure measurement. To answer this question it helps to look at this is 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 really 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 is denoted with the subscript ?abs?: Results .
Definition of gauge pressure
The gauge pressure is defined as the difference between an absolute 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 is usually the difference from the existing ambient pressure that’s measured. However, this pressure changes with the weather and the height above sea level. A complete pressure measurement measures the difference from the perfect or absolute vacuum. This is exactly 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 could be differentiated the following: in most cases, the measuring task is to determine the gauge pressure. For this reason this sort of sensor is most widely used. However, if a gauge pressure sensor is used in an application in which the actual measuring task is 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 selection of 1 bar) or negligible (in hydraulics at 400 bar).
Note
When you are 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.