GAUGE PRESSURE AND ABSOLUTE PRESSURE - Gauge pressure and absolute pressure are the two most common pressure measurement systems. They have a huge significance in the different fields of engineering. The basic difference between the two is that the Gauge pressure uses atmospheric pressure as the zero point and the absolute pressure uses absolute zero as the zero point. The gauge pressure doesn’t give the precise measure due to the continuous change in the atmospheric pressure whereas the absolute pressure always gives the accurate readings.

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Gauge Pressure And Absolute Pressure

Difference Between Gauge Pressure And Absolute Pressure Explained

engineeringinsider.org

Pressure is the force applied per unit surface area. Yes, it is the simplest way to define the pressure.

There are various systems through which pressure is measured.

Gauge pressure and absolute pressure are the two most common pressure measurement systems. They have a huge significance in the different fields of engineering.

Both the pressure systems have their own applications. The basic difference between the two is that the Gauge pressure uses atmospheric pressure as the zero point and the absolute pressure uses absolute zero as the zero point.

The gauge pressure doesn’t give the precise measure due to the continuous change in the atmospheric pressure whereas the absolute pressure always gives the accurate readings.

Let us go through both of them-

Gauge pressure

Denoted by ‘g’ after mentioning the pressure unit. It is the most common pressure reference and is measured in reference to the atmospheric pressure.  

However, change in the atmospheric pressure will directly result in the varying output of the gauge pressure sensor.

Gauge pressure higher than the ambient pressure is positive pressure and below is negative pressure or vacuum gauge pressure.

Usually, the gauge pressure sensor has got only one pressure port. The atmospheric air pressure is directed by a vent tube to the sensing element.

Since it always measures the pressure with respect to the atmospheric barometric pressure, the outside air can meet the negative side of the pressure sensing diaphragm which is allowed by the transmitter.

This is the reason why the vented gauge pressure shows zero reading when the connection of process pressure is kept open to atmospheric air.

Absolute pressure -

It can be defined as the pressure of perfect vacuum space. Absolute zero is taken as the reference point for measuring the absolute pressure.

The measurement of barometric pressure is the perfect example of absolute pressure.

The manufacturer seals a high vacuum with a sensing diaphragm to produce an absolute pressure sensor.

Therefore, the barometric pressure will be shown in the actual reading if the process pressure connection of the absolute pressure transmitter to the air is held open.

If you want to control a pressure or measure it, that is affected by the atmospheric pressure, for example, the level of water in an open tank, you would select a vented gauge pressure as you want the pressure reading minus atmospheric pressure.

Also, if you want to measure the pressure that is not affected by the change in atmospheric pressure, like for leak testing of a completely sealed non-flexible container, you would use the absolute pressure sensor.

The final reading will var if the gauge pressure sensor is used to measure the container pressure. 

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