The pressure on a fluid is measured in two different system. In one system, it is measured above the absolute zero or complete vaccum and it is called the absolute pressure and in other system pressure is measured above the atmospheric pressure and it is called gauge pressure.
Absolute pressure:-
It is defined as the pressure which is measured with reference to absolute vaccum pressure.
Gauge pressure:-
It is defined as the pleasure which us measured with the help of pressure measuring instrument, in which atmospheric pressure is taking as datum.
Atmospheric pressure on the scale is marked as zero.
Vaccum pressure:-
It is defined as the pressure below ther atmospheric pressure.
Mathematically:-
i. Absolute pressure
= Atmospheric pressure + Gauge pressure
ii. Vaccum pressure
= Atmospheric pressure - Absolute pressure
- The atmospheric pressure at sea level at 15°C is 101.3 KN/m^2 or 10.83 N/cm^2.
- MKS unit of atmospheric pressure is equal to 1.033Kgf/cm^2.
Measurment of pressure:-
The pressure of fluid is measured by ther following devices:-
1. Manometer
2. Mechanical gauge
1. Manometer:-
It is defined as the device's used for measuring the pressure at a point in a fluid by balancing the column of fluid by ther same or other column of the fluid.
They are classified as:-
a. Simple Manometer
b. Differential Manometer
2. Mechanical gauge:-
Mechanical gauge are defined as the device used for measuring the pressure by balancing the fluid column by ther shoring or dead weight.
The commonly used mechanical pressure gauge are:-
a. Diaphragm pressure gauge
b. Bourdon pressure gauge
c. Dead weight pressure gauge
d. Belows pressure gauge.
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