Today we will learn about difference between gauge pressure
and absolute pressure. Pressure is defined as a normal force exerted by a fluid
per unit area. It is defined only in liquid or gas state. In the solid state
the normal force per unit area is called stress. SI unit of pressure is Pascal.
One Pascal is equal to one newton per meter square pressure. MTS unit of
pressure is KG/cm2. Sometimes pressure
is measure in respect of water column. Ten meter water column (mmwcl) is equal
to one KG/cm2 pressure.
These all are small unit of pressure. The atmospheric or
large quantity of pressure is measured in bars where one bar is equal to 100000
Pa pressure. One bar is also defined as 1.019 Kg/cm2 pressure. The standard value of atmospheric
pressure is one bar.
According to the measurement pressure can be divided into
two categories. The first one is known as gauge pressure and other one is
absolute pressure. We will learn the difference between them in detail.
Difference between Gauge Pressure and Absolute Pressure:
Absolute Pressure:
The actual pressure at a given position is called the
absolute pressure and it is measured relative to absolute vacuum. One concept remembers
in mind that to measure any quantity we required a base line with respect we are
going to measure it.
To learn this concept supposes we need to measure distance
of Bombay. Distance can be measured in meter. Can we measure distance of Bombay by this input? Obviously your answer is no because we need a reference from
which we want to measure distance. Now suppose we need to measure distance of
Bombay from Delhi. Now we are able to measure this distance in some meters or kilometers.
Similarly pressure cannot be measured without a reference.
When we take vacuum or no pressure condition as reference the measured pressure
is called absolute pressure.
Gauge Pressure:
When we take atmospheric pressure as reference to measure
pressure of any system, the measured pressure is known as gauge pressure. Most
of pressure devices work in atmospheric condition always measure gauge
pressure. We can convert this gauge pressure in absolute pressure by adding
atmospheric pressure in gauge pressure.
P (absolute) = P
(Gauge) + P (Atmospheric)
Most of gauge read zero in atmosphere but there is some
atmospheric pressure. They read atmospheric pressure as absolute zero pressure.
Pressure below atmospheric pressure is called vacuum pressure and is measured
by vacuum gauges that indicate the difference between the atmospheric pressure
and absolute pressure.
P (vacuum) = P (Atmospheric) – P (Absolute)
This is all about gauge pressure and absolute pressure. If
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