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Pressure Reference

Pressure Reference Chart

Atmospheric / Barometric Pressure

Pressure Type:

Gage
(PSIG)

Absolute
(PSIA)

Vacuum
(PSIV)

Compound
(PSIV - PSIG)

Elevated
(PSIG)
or (PSIA)

Sealed Gage
(PSIS(SG))

 Differential
(PSID)

Pressure Reference:

Atmosphere Vented

Vacuum Sealed

Atmosphere Vented

Atmosphere Vented

Atmosphere or Vacuum

Atmosphere Sealed

Low Side

Definition:

Units above atmosphere

Units above full vacuum

Units below atmosphere

Units above and below Atmosphere

Units above an offset

Units above a sealed reference

Units between two unknown pressures

Pressure Reference Definitions

Gage Pressure:  Pressure measured above local ambient atmospheric pressure.  Sensor has a reference that is exposed to atmosphere.Common applications are Hydraulics, Pneumatics and liquid level.

Sealed Gage Pressure:  Gage Pressure measured above a sealed pressure reference.  The reference pressure is hermetically sealed at some ambient pressure so that the reference remains static.    Used for high pressure applications where daily atmospheric pressure changes are insignificant relative to the measured pressure.  Common applications are Hydraulics, Pneumatics and High pressure pumps/compressors.

Vacuum Pressure: Pressure measured below local ambient atmospheric pressure.  Sensor has a reference that is exposed to atmosphere. Sometimes referred to as “negative” pressure. The sensor is referenced to atmosphere and the output (usually) increases as the pressure decreases. Typical applications are vacuum molding, flow detection and gas sampling.   

Absolute Pressure:  Pressure measured above a full vacuum.  The sensor reference is evacuated and hermetically sealed so that it remains static (some manufactures electronically offset the zero).    The most common application is to measure atmospheric pressure.

Differential Pressure:  The difference between two unknown pressures.  Sensor has a high side port and a low side port and the output is the difference between the two. Common applications for differential pressure sensors include flow (across an orifice) and level of a fluid in a sealed container.

Compound Pressure:
  Pressure measured above and below local ambient atmospheric pressure.  The reference side of the sensor is open to atmosphere.  Application: Automotive manifold pressure.

Elevated Pressure:  Pressure measured above a reference usually atmospheric (gage) but could also be a vacuum (absolute) with an artificial (suppressed) zero.  A common application is water tower level measurement where only the level in the elevated tank is needed not the head pressure in the pipe leading up to the tank.