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 this is of gauge pressure and absolute pressure. Naughty between the two measurements is then explained relatively simply and thus also the decision 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 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). It is denoted with the subscript ?e?: Pe and is calculated as follows: 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’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. Because of this , this measurement is independent of environmental influences such as for example weather or altitude. Which measurement is now the right one?
In practice, the two measurements could be differentiated as follows: normally, the measuring task is to determine the gauge pressure. That is why this type of sensor is most widely used. However, if a gauge pressure sensor is used in an application in which the actual measuring task would be to gauge the absolute pressure, the next additional errors must 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 regards to the measuring range, these errors can be substantial (e.g. in pneumatics at a measuring range of 1 bar) or negligible (in hydraulics at 400 bar).
Note
For anyone who is uncertain whether your measuring task needs a complete pressure or gauge pressure measurement, simply contact us ? we?ll be glad to work with you.