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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 this is of gauge pressure and absolute pressure. The difference 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. diaphragm seal is denoted with the subscript ?abs?: Pabs.
Definition of gauge pressure
The gauge pressure means the difference between a complete 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 current ambient pressure that is measured. However, this pressure changes with the elements and the height above sea level. An absolute pressure measurement measures the difference from the ideal or absolute vacuum. This is the reason this measurement is independent of environmental influences such as 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 exactly why this type of sensor is hottest. However, if a gauge pressure sensor can be used in an application in which the actual measuring task would be to gauge the absolute pressure, the following additional errors should be expected:
+/- 30 mbar due to changes in weather
around 200 mbar when changing the location (e.g. from sea level to 2,000 m)
With regards to the measuring range, these errors could be substantial (e.g. in pneumatics at a measuring range of 1 bar) or negligible (in hydraulics at 400 bar).
Note
When you are 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.