Again and again, we are asked the question about 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 the two measurements is then explained relatively simply and therefore also the choice of the appropriate 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 really is denoted with the subscript ?abs?: Pabs.
Definition of gauge pressure
The gauge pressure is defined as the difference between a complete pressure (Pabs) and the prevailing atmospheric pressure (Pamb). Snotty is denoted with the subscript ?e?: Pe and is calculated as follows: Pe = Pabs ? Pamb.
Absolute vs gauge pressure measurement
The difference between the 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 ideal or absolute vacuum. This is why this measurement is independent of environmental influences such as weather or altitude. Which measurement is now the right one?
In practice, both measurements can be differentiated as follows: usually, the measuring task is to determine the gauge pressure. Because of Fundamentals , this type of sensor is most widely used. However, in case a gauge pressure sensor can be used in an application in which the actual measuring task would be 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)
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
Should you be uncertain whether your measuring task needs an absolute pressure or gauge pressure measurement, simply e mail us ? we?ll be glad to assist you.