Difference Between Gauge Pressure and Absolute Pressure (With Table)

These two important terms play a major role in physics or mechanical engineering. We all know the basic term pressure. The force applied per unit area to an object perpendicular to the surface of the object. The SI unit is Pascal. Next, we will learn about two main types of pressure. Understand the difference between overpressure and absolute pressure.

Gauge Pressure vs Absolute Pressure

The main difference between gauge pressure and absolute pressure is that gauge pressure is the difference between absolute pressure and atmospheric pressure. Absolute pressure is the sum of excess pressure relative to atmospheric pressure.  Atmospheric pressure here refers to the atmospheric pressure of the entire earth or the Air Force. 

Another name of gauge pressure is “Overpressure” which means the pressure of the system applied above atmospheric pressure. Gauges pressure measured in the gauges means one by one. The formula to calculate is Pg=P-Pa means the subtraction of system pressure and atmospheric pressure. It is denoted by “g”.An example of gauge pressure is pressure measurement.

As the name suggests so when we measure Absolute pressure gives the exact value while measuring. In this Absolute pressure, we calculate the pressure of vacuum space with no matter. The formula for calculating is Pabs= Pg+ Patm. An example of absolute pressure is a measurement of barometric pressure.

Comparison Table Between Gauge Pressure and Absolute Pressure

Parameters of ComparisonGauge PressureAbsolute Pressure
FormulaPg=P-Pa.Pabs+Pg+Patm.
ApplicationUsed to measure the vapor pressure of vacuum reactors, blood pressure, liquid pressure, vehicle tires,  etc.Used to measure pressure for industrial purposes, refineries, scientific calculations, etc.
Instrument.Most of the time Bourdon tube pressure gauge is used to measure pressure.A barometer or manometer is used to measure absolute pressure.
Preciseness.Measurement of gauge pressure is not so precise.Measurement of absolute pressure is always precise.
Referenced.It is zero referenced against ambient pressure.It is zero referenced against vacuum space.
ValuesIts value can be a positive value or negative value.Absolute pressure always comes in positive.
UnitsUnits of gauge pressure measurement are psig,kPag, and barg. P is pascal and g is a suffix of gauge.Units of absolute pressure measurement are Asia and kpaa. Here P is pascal and a is a suffix of absolute.

What is Gauge Pressure?

The gauge pressure gives readings of the pressure to the weight of the atmosphere. Its value varies according to weather conditions or height above sea level. It is also called overpressure. When the value of overpressure is positive, absolute pressure is greater than atmospheric pressure. 

when the value of overpressure is negative means absolute pressure is less than atmospheric pressure. This can be measured with a membrane sensor that faces the pressure medium on one side and atmospheric pressure on the other side. When measuring overpressure, keep in mind that weather conditions can change at any time, so the values ​​can fluctuate. The diaphragm is made of ceramic and steel. The term overpressure is used when the pressure in the system is higher than the local atmospheric pressure. The gauge pressure scale is based on zero and shows a zero value when opened to the atmosphere. 

That’s why it is also named gauge pressure zero-referenced against atmospheric pressure. It is the most useful pressure measurement for any practical application. It is easy to calculate when you have one value. The gauge can be determined by the difference of total pressure by the pressure of one atmosphere.

What is Absolute Pressure?

This pressure is a measure of the amount of pressure applied by a gas, liquid, or vapor in a complete vacuum. Complete vacuum means a fixed reference for measuring absolute pressure. This is measured by an electrofilm sensor that measures pressure on one side or is exposed to a closed vacuum on the other side and is firmly fixed. 

Provides accurate measurements. In most cases, barometric pressure is required for accurate altitude pressure measurements. We mainly find the absolute pressure that weather conditions change in high and low. We are also looking for absolute pressure at the atmospheric level. If pressure above zero is observed, the absolute pressure is known. It is also called complete vacuum pressure because it applies atmospheric pressure and overpressure. 

Sometimes it happens that the atmosphere changes its condition constantly then we have to measure pressure in pounds per square inch absolute i.e. PSIA. The best example of Absolute pressure is to predict weather changes. Furthermore, an example of Absolute pressure is in food packaging, gas analysis, aeronautics systems. As the name suggests absolute(complete)  so it is very important to measure pressure with full concentration because any wrong value of pressure measurements leads to major data errors.

Main Differences Between Gauge Pressure and Absolute Pressure

  1. The most common and important difference you see is that gauge pressure measurement is not so accurate whereas absolute pressure measurement gives an accurate measurement.
  2. For small measurement work, we find gauge pressure whereas Absolute pressure measurement is used for industrial purposes.
  3. Gauge pressure is not used for gas or liquid pressure calculations because it does not give a true pressure value whereas Absolute gives a more precise value while calculating the pressure of the gas, liquid.
  4. Gauge pressure is referred to as atmospheric pressure whereas  Absolute pressure is referred to against a perfect vacuum.
  5. Gauge pressure is also called overpressure whereas Absolute pressure is named total system pressure.
  6. Whenever changes occur in the atmosphere, the gauge pressure value is affected whereas the change in the atmosphere doesn’t affect the value of absolute pressure measurement.

Conclusion

We hope you understand all the terms related to pressure and its main types: gauge pressure and absolute pressure. I try my best to explain all these two terms with their differences. These all terms are a part of the mechanical department. We all see the weather measurement value and all other pressure measurements value all these measurements come from the use of these absolute and gauge pressure instruments.

Most basic terms are used in this article like surroundings, system, etc. For that, you need to understand the first thermodynamics chapter clearly. Because all these practical terms are correlated to each other.

References

  1. https://link.springer.com/article/10.1007/s12647-019-00328-6
  2. https://iopscience.iop.org/article/10.1088/1361-6501/aa92ea/meta
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