TYPES OF

PRESSURE MEASUREMENTS

The relationships between gauge and absolute pressure are critical 2

Pressure Line

0 PSIA 14.7 PSIA

100 PSIA 114.7 PSIAVacuum Range

14.7 PSIV-1 ATM0 “ Hg

0 mB/hPa0 Torr A

0 PSIVATM

29.92 "Hg1013 mB / hPa

760 Torr A

Atmospheric Pressure-14.7 PSIG 0 PSIG

85.3 PSIG 100 PSIG

85.3 PSIC

Absolute Pressure

Definition: Pressure measured relative to full vacuum (refers to a true zero reference)

Units of Measure:Pounds per square inch absolute or (PSIA)

Applications: best used in applications that require higher accuracies over large temperature range or for comparative studies at different elevations

Atmospheric Pressure

Definition: Pressure of the atmosphere at the earth’s surface. At sea level this pressure is not constant (it varies with the weather) but averages around 100 kilopascals (kP). One atmosphere is also approximately the ambient pressure at sea level and is equal to 14.7 PSIA

Units of Measure:pounds per square inch (psi), atmospheres (atm), mb, hPa can measure ambient pressure in other circumstances

Applications: remote weather stations, test stand reference pressure

Barometric Pressure

Definition: The measure of atmospheric pressure

Units of Measure:Often measured in millibars, in Hg (inches of mercury), or hector pascalsIn other circumstances ambient pressure may be measured in pounds per square inch (PSIA)

Applications: airports, AWOS systems, humidity measurements, data buoys

Compound Pressure

Definition: Pressure measured from full vacuum (-14.7 PSIV) through atmospheric pressure to a positive gauge pressure, being referenced to current atmospheric pressure

Units of Measure:pounds per square inch compound (PSIC)

Applications: autoclaves, instrument sterilization, pumps

Differential Pressure

Definition: Pressure measured relative from one pressure to another

Units of Measure:pounds per square inch differential or (PSID)

Applications: filter status, static pressure, chillers, sealed tank

Gauge Pressure

Definition: A form of atmospheric pressure measured relative to ambient atmospheric pressure

Units of Measure:pounds per square inch (PSIG)

Applications: measuring pressure in vented tank (link to app note), pumps, compressors, test stands

Vacuum Pressure

Definition: Generally refers to pressures below atmospheric pressure

Units of Measure:pounds per square inch vacuum (PSIV) or 0-30”Hg

Applications: semiconductor fabs, plasma sterilizers, vacuum packaging