What is Pressure?
The pressure is the force extorted by a medium like liquids, gases, and solids. The pressure is measured by the force per unit area. So we have a mathematical formula of pressure that is
Pressure = Force/Area
Let say, force is in N (Newton) and Area is in mm (millimeters) than, SI unit of pressure is N/mm².
The pressure is the measurement quantity that describes a system. Usually, the pressure differences are used as a means of measuring the flow rate of the fluids. The pressure is invariably significant process parameter.
What is the pressure gauge?
The pressure gauge is measured above the local atmospheric pressure. And the total pressure is some of the 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)
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Types of pressure gauge
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 readout scale,
Some Disadvantages of Manometers
- 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.
For high-pressure conditions, U-tube type manometer is used. U-tube manometer consist of two limbs, often made of steel, where one limb has a larger diameter than the other.
The function of Ring Balance is like mechanical displacement. It is mechanical displacement-type pressure measuring devices.
It looks like a composed ring, the lower section of the annular ring is also filled with a sealing fluid like water or mercury. The main ring balanced on a knife-edge on its center for the reason of free rotation.
An additional mass is attached to the lower part of the ring.
Let’s say, P1 = High pressure
P2= Low pressure and the turning moment is defined by Tm=(P1-P2)Ari
Inverted Bell Manometer
An inverted bell manometer is another pressure measuring device that is of the mechanical displacement type.
As the 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 the interior and exterior surfaces of the bell.
The type of manometer is capable of measuring absolute, positive, negative and differential pressure.
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Preview, Chapter-7 | Temperature Measurement