Description and Functionalities
Monitoring of SF
6
gas
P20--0001EN/02
3/6
01--2011
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GRID
Calculating the pressure
Relative pressure?
Absolute pressure?
Absolute pressure = relative pressure + atmospheric pressure
Pressure Description Illustration
Relative
The pressure of the SF
6
gas is
measured using an industrial---
type pressure guage. This
pressure gauge has a
distortable membrane that
guides an indicating needle.
Onse side of the membrane is
in contact with the SF
6,the
other with the atmosphere. The
pressure difference between the
gas and the atmosphere is
measured : with the
atmospheric pressure as a
reference, only the relative
pressure of the SF
6
is
measured. The relative
pressure of the SF
6
gas
therefore depends on the local
atmospheric pressure at the
time of measurement.
SF
6
Atmospheric pressure
Industrial pressure guage
Absolute
If the membrane is distortable,
in contact on one side with the
SF
6 gas, on the other a
vacuum, the pressure gauge
measures the pressure
difference between the SF
6 and
the vacuum. As the vacuum has
a value of zero, the pressure
gauge measures the absolute
pressure of the mix. The
absolute pressure of the SF
6
gas, which is independent of the
atmospheric pressure,
descrives the quantity of gas
introduced in the compartment,
and therefore characterises the
the density of the SF
6
gas at a
given temperature. To measure
it, an absolute pressure gauge
is required,which is an
instrument that is less common
and more delicate than a
relative pressure gauge. This
is
why a relative pressure
gauge
is used, making corrections
for
atmospheric pressure
variations
due to atmospheric
distur-
bances and altitude variations
.
SF
6
Vacuum compartment
Absolute pressure
gauge
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