Again and again, we are asked the question concerning the difference between a complete 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 decision of the appropriate measurement.
Definition of absolute pressure
Absolute pressure is 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 really is denoted with the subscript ?abs?: Pabs.
Definition of gauge pressure
The gauge pressure means the difference between an absolute 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 existing 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 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 currently the right one?
In practice, the two measurements can be differentiated the following: generally, the measuring task would be to determine the gauge pressure. Because of Desperate , 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 would be to gauge the absolute pressure, the following additional errors should 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 selection of 1 bar) or negligible (in hydraulics at 400 bar).
Note
For The Truth 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.