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 your two measurements is then explained relatively simply and thus also the choice of the appropriate 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 is 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 really 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 usually the difference from the existing ambient pressure that’s measured. However, this pressure changes with the weather and the height above sea level. ไดอะแฟรม ซีล measures the difference from the perfect or absolute vacuum. For this reason this measurement is independent of environmental influences such as weather or altitude. Which measurement is currently the right one?
In practice, the two measurements can be differentiated as follows: usually, the measuring task would be to determine the gauge pressure. That is why this kind of sensor is hottest. However, in case 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 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)
According 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
Should you be uncertain whether your measuring task needs a complete pressure or gauge pressure measurement, simply e mail us ? we?ll be pressure gauge octa to work with you.