Difference between gauge pressure and absolute pressure measurement

Again and again, we are asked the question concerning the difference between an absolute pressure measurement and a gauge pressure measurement. To answer Speedy helps to look at this is of gauge pressure and absolute pressure. The difference between the two measurements is then explained relatively simply and therefore also the decision of the correct measurement.
Definition of absolute pressure
Absolute pressure is 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 means the difference between a complete 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 the two measurements is relatively easily clarified: in a gauge pressure measurement, it is always the difference from the current 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. This is exactly why 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 the following: in many instances, the measuring task would be to determine the gauge pressure. This is the reason this sort of sensor is hottest. However, if a gauge pressure sensor is used in an application where the actual measuring task is to gauge the absolute pressure, the following additional errors must be expected:
+/- 30 mbar caused by 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 can be substantial (e.g. in pneumatics at a measuring range of 1 bar) or negligible (in hydraulics at 400 bar).
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Should you be uncertain whether your measuring task needs a complete pressure or gauge pressure measurement, simply contact us ? we?ll be glad to assist you.

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