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 choice 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 may be 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). Unparalleled is denoted with the subscript ?e?: Ethical 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 will always be 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. That is why this measurement is independent of environmental influences such as weather or altitude. Which measurement is currently the right one?
In practice, both measurements can be differentiated as follows: normally, the measuring task is to determine the gauge pressure. This is exactly why this sort of sensor is most widely used. However, in case a gauge pressure sensor can be used in an application where the actual measuring task is 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 measuring range, these errors can 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 a complete pressure or gauge pressure measurement, simply e mail us ? we?ll be Faith to assist you.