Basics of Pressure Measurement

Both liquids and gases have the ability to flow, which is why they are collectively called fluids and tend to disperse any force applied to them.

It is especially useful to quantify force applied to a fluid in terms of force per unit area.

P = F/A

In the metric system, it is the pascal (Pa), defined as one Newton (N) of force per square meter (m2) of area.

In the British system, it is pounds per square inch (PSI), pounds (lb) of force per square inch (in2) of area.

For conversion from the metric system to the British system and vice versa following the link:

https://www.unitconverters.net

Generally,100 Kpa or 1 Bar = 14.5 PSI

Atmospheric Pressure (P_atm): It is the pressure within the atmosphere of Earth.

https://en.wikipedia.org/wiki/Atmospheric_pressure

Gauge Pressure (P_g): It is the pressure relative to atmospheric pressure. Positive for pressures when above atmospheric pressure and negative for pressures when below it.

Absolute Pressure (P_abs): Absolute pressure is the sum of gauge pressure and atmospheric pressure.

P_abs = P_g + P_atm

Pressure is the primary process variable for a wide range of process measurements. Many types of industrial measurements are inferred from pressure, such as:

• Flow (measuring the pressure drop across a restriction)
• Liquid level (measuring the pressure created by a vertical liquid column)
• Liquid density (measuring the pressure difference across a fixed-height liquid column)
• Weight (hydraulic load cell)

Pressure Measurement Technologies/Methods:

1. Manometers
2. Mechanical Pressure Sensors
3. Electronic Pressure Sensors

Pressure Measuring Instruments:

1. Manometers
2. Gauges
3. Transmitters
4. Switches

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