GE SF6, Instruction Manual

Page: 35 / 300

Description and operation
SF
6
gas monitoring
GE Information
07- 2016 L20- 001EN/08
3/6
Pressure measurement
Effective pressure ?
Absolute pressure ?
Absolute pressure = effective pr atmospheric pressure
Pressure Description Diagram
Effective
The pressure of SF
6
gas is meas-
ured by of a standard pressure
gauge with a deformable dia-
phragm actuating an indicating
pointer.
One surface of the diaphragm is
in contact with the SF
6
gas, while
the other is in contact with the
atmosphere. The difference
between the gas and the atmo-
sphere is thus measured, taking
atmospheric pressure as a refer-
ence. This is the measurement of
the effective pressure of the SF
6
gas.
SF
6
Atmospheric pressure
Standard pressure gauge
Absolute
If the deformable diaphragm, one
surface of which is in contact with
the SF
6
gas, blocks a volume
where a vacuum has been
developed, the pressure gauge
measures the pressure differ-
ence between that of the SF
6
gas
and the vacuum. Since the latter
is zero, the pressure gauge
measures the absolute pressure
of the gas.
The absolute pressure of the SF
6
gas, independent of atmospheric
pressure, reflects the quantity of
gas introduced into the compart-
ment and hence its density at the
present temperature.
This is measured by means of an
absolute pressure gauge which
is less generally used and more
delicate than a effective pressure
gauge. This is the reason why a
effective pressure gauge is used,
provision being made for correc-
tions required by atmospheric
pressure variations resulting
from atmospheric disturbances
and differences of elevation.
SF
6
Vacuum volume
Absolute
pressure gauge