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Absolute Pressure:
When any pressure is deducted from the absolute zero pressure, it is called absolute pressure. It is measured using a barometer and it is equal to measuring pressure plus the atmospheric pressure.
Diagram showing absolute pressure vacuum and gauge
Absolute pressure formula is given by
Pabs = Patm + Pgauge
Where,
Pgauge is the gauge pressure.
PATM atmospheric pressure
The vacuum pressure is calculated as:
Vacuum pressure = atmospheric pressure – absolute pressure.
At sea level it is around 14.7 Pounds per square inch.
What is absolute pressure?
There is absolute zero pressure in space that is in a vacuum.
We have two ways of measuring pressure depending on which we use as a reference these are
- Absolute pressure
- Gauge pressure
One way to measure pressure is to use absolute zero pressure such as in space. This will be like the base value against which other pressures are measured.
Therefore, the pressure measured relative to this absolute zero pressure in a vacuum is called absolute pressure. A pressure measurement below this atmospheric pressure is called negative pressure also as vacuum pressure.
Scientists have found such a vacuum through behind a diaphragm in the sensor.
They do this by removing the air and then selling it to prevent it from direct contact with the outside.So absolute pressure is also known as sealed pressure. It’s a unit of psi (i.e) pound per square inch absolute. This is very helpful because even if the outside ambient pressure changes, we may have an accurate method to measure the pressure.
Solved problem :
Problem: 1
Find the absolute pressure for cage pressure 29 PSI and atmospheric pressure 13 PSI.
Solution:
Since Pabs = Patm + Pgauge
Here Patm = 13 psi and Pgauge = 29 psi
Pabs = 13 + 29 psi = 42 psi
Problem: 2
Find the absolute pressure for cage pressure 45 PSI and atmospheric pressure 20 PSI
Solution:
Since Pabs = Patm + Pgauge
Here Patm = 45 psi and Pgauge= 20 psi
Pabs = 45 + 20 psi = 62 psi
