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What is the difference between absolute sealed and differential

Pressure sensors measure pressure in comparison to a reference pressure and can be divided into:

  • Absolute
  • Sealed gage
  • Vented gage and
  • Differential

These terms will be explained on the basis of MeasureX pressure sensors and transducers and their availability is mentioned in data sheet of every product.

Figure: Comparison of absolute, gage and differential pressure

Absolute pressure: Absolute pressure is referenced to the vacuum of free space (zero pressure). MeasureX absolute pressure sensors offer ranges from 0.1bar to more than 1000bar.

Figure: Principle of an absolute pressure sensor

Vented Gage pressure: Gage pressure is measured relative to the ambient atmospheric pressure. The average atmospheric pressure at sea level is 1.01325bar. Changes of the atmospheric pressure due to weather conditions or altitude directly influence the output of a gage pressure sensor. A gage pressure higher than ambient pressure is referred to as positive pressure. If the measured pressure is below atmospheric pressure it is called negative or vacuum gage pressure.

Gage pressure sensors only offer one pressure port. The ambient air pressure is directed through a vent hole or a vent tube at the back side of the sensing element.

Figure: Principle of a gage pressure sensor

Sealed Gage pressure: It is possible to seal and block the vent hole in the factory. The advantage of this sealing is that, pressure on back of the sensor will be constant and equal to atmospheric pressure in the manufacturing company. Therefore it is not changing by change of atmospheric pressure in different places.

Differential pressure: Differential pressure is the difference between any two process pressures p1 and p2. Therefore, differential pressure sensors must offer two separate pressure ports with tube or threaded connections. Pressure sensors and transmitters that are able to measure positive and negative pressure differences, i.e. p1>p2 and p1<p2, are called bidirectional differential pressure transducers.

Figure: Principle of a differential pressure sensor