Types of pressure

Types of pressure

Pressure is an expression of force exerted on a surface per unit area. In this article, you found Types of pressure.

Gauge Pressure

The most common measurement of pressure is gauge pressure which is the pressure difference between the measured pressure and ambient pressure.

The term pressure is used if the measured pressure is higher than the atmospheric pressure. The term vacuum is used if the measured pressure is below atmospheric pressure.

The use of either of these terms automatically implies that the pressure (or vacuum) being measured is with respect to ambient pressure

(i.e. gauge pressure or vacuum).

In order to distinguish absolute pressure measurements, the words “absolute pressure” must be used.

Gauge Pressure uses a reference to the atmosphere around the sensor. Because the sensing element has a deflection due to a pressure change, a reference point is needed to know exactly what pressure is being measured.

Pressure sensors that use gauge pressure—typically seen in PSIG, BARG, and kPaG —have some type of vent.

This vent can be built into the sensor or even through a tube in the electrical connection. The vent is positioned to use atmospheric pressure as a reference point for the sensor to measure the media.

One common reason for using gauge pressure is to ensure that with any location throughout the world, the sensor will always reference the location in which it is installed.

Absolute Pressure

The most definite reference point is absolute zero pressure.

This is the pressure of empty space in the universe. When pressure is based on this reference point, it is called absolute pressure.

To distinguish it from other types of pressures it is accompanied by the suffix “a” or “abs” (from the Latin: absolutus = independent, separate from).

Absolute Pressure a perfect vacuum as its reference. This type of pressure reference is the gauge pressure of the media plus the pressure of the atmosphere.

As locations change, especially when dealing with elevation changes, the reference point can change because of atmospheric pressure differences.

Using an absolute pressure sensor eliminates the reference to a varying atmospheric pressure and relying on a specific pressure range for reference.

Differential pressure

Differential Pressure can be a little more complex than gauge or absolute but is simply measuring the difference between two media.

Although most gauge pressures are technically a differential pressure sensor—measuring the difference between the media and atmospheric pressure—a true differential pressure sensor is used to identify the difference between the two separate physical areas.

For example, the differential pressure is used to check the pressure drop—or loss—from one side of an object to the other.

The difference between the two pressures P1 and P2 is referred to as the pressure differential                ΔP = P1 – P2.

The difference between two independent pressures is called the differential pressure

Atmospheric pressure

The most important pressure for life on earth is atmospheric air pressure pamb (amb = ambient, surrounding).

It is produced by the weight of the atmosphere surrounding the earth up to an altitude of about 300 miles.

Atmospheric pressure decreases continuously up to this altitude until it practically equals zero (full vacuum).

Atmospheric air pressure undergoes climatic changes, as shown by the daily weather report.

At sea level, pamb has an average value of 29.90 inches of Mercury (“Hg). In high or low-pressure weather zones it can fluctuate by as much as ± 5%.

 Five main units of pressure

The unit of pressure in the SI system is the pascal (Pa), defined as a force of oneNewton per square meter. The conversion between atm, Pa, and torr is as follows: 1 atm = 101325 Pa = 760 torr.

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