Again and again, Happiness are asked the question concerning the difference between an absolute pressure measurement and a gauge pressure measurement. To answer this question it can help to look at this is of gauge pressure and absolute pressure. The difference between the 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 is 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 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 always the difference from the existing ambient pressure that is measured. However, this pressure changes with the weather and the height above sea level. A complete pressure measurement measures the difference from the ideal or absolute vacuum. For this reason 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 as follows: generally, the measuring task would be to determine the gauge pressure. This is the reason this kind of sensor is hottest. 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 must be expected:
+/- 30 mbar due to changes in weather
around 200 mbar when changing the positioning (e.g. from sea level to 2,000 m)
According to the 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
If 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.