Pressure is an important process variable.
Pressure is defined as force per unit area.
Pressure = Force / Area
Force can be represented as Pound force,Kilogram force,Newton,dyne
Area can be represented as Square inches,Square feet,Suare Centimeter, Square Meters
Common units of Pressure include:
1.Pounds per square inch (psi)
2.Newton/m2 (=Pa) : SI unit
Inches(or mm) of water(or Hg)
Atmosphere(1 atm = 760 mm Hg)
Torr (1 mm of Hg)
Gauge Absolute and Atmospheric pressure
Gauge pressure : Pressure above atmospheric is called gauge pressure.
Vacuum Pressure: Pressure below atmospheric is a vacuum (negative gauge pressure)
Absolute pressure: Absolute pressure is measured from a perfect vacuum