The pressure gauge is measured above the local atmospheric pressure. And the total pressure is the some of atmospheric pressure and gauge pressure. The differential pressure is the difference of pressure measured in two points. Some other technical terms are absolute pressure(measured above total vacuum or zero) and zero absolute (represents the total lack of pressure).
There are a number of things to take into account while specifying the right pressure gauge for your application. This goes from choosing the right measuring range, choosing the diameter of the dial, to preventing the pressure gauge from being subject to vibrations and even more of this kind of choices.
Types of pressure gauges
Manometers
Manometers used as the primary standards for pressure measurement. Due to temperature variation the expansion of fluid filled in manometer affects their density and precision of measurement is affecting by the thermal expansion of the read out scale.
The filling fluid is subjected to vaporization at high temperature and vacuum. Evaporation of fluids at low pressure and high temperature conditions. Toxicity of mercury.
U-tube Manometer
For high pressure conditions U-tube type manometer is used. U-tube manometer consist of two limbs,often made of steel, where one limb have a larger diameter than the other.
Ring Balance
The function of Ring Balance is like mechanical displacement. It is mechanical displacement type pressure measuring devices.
Inverted Bell Manometer
An inverted bell manometer is another pressure measuring device that is of the mechanical displacement type. As name suggests the bell is immersed in the sealing fluid in an upside down position. The inverted bell moves in the vertical direction due to the different pressure arising out of the pressure between interior and exterior surfaces of the bell.
The type of manometer is capable of measuring absolute, positive, negative and differential pressure.
