Description and operation
SF
6
gas monitoring
L20--001EN/04
4/6
01--2003
E ALSTOM
Measuring density
Pressure units
D The international unit pressure is the Pascal (Pa).
D The practical unit is the bar (14.503 p.s.i.)
1 bar = 1,000 hPa
1 bar = 100 kPa
10 bar = 1 MPa
D Standard atmospheric pressure is equal to 101.3 kPa at sea level and an
air temperature of 20°C(68°F).
Measuring density
When it is not possible to directly measure density, this may be checked
using an industrial pressure gauge capable of measuring the
effective
pressure
.
An effective pressure value corresponds to the rated density, determined
for normal atmospheric pressure (101.3 kPa) and an ambient temperature
of 20°C(68°F).
For each pressure reading (filling, inspection of densimeter thresholds...),the
rated effective pressure should be corrected according to the ambient tem-
perature and atmospheric pressure of the site at the time the reading is taken.
See the module “Calculation of the SF
6
gas filling pressure to using the
pressure gauge (tool)”.
The real pressure is therefore :
P
real
= P
rated effective in accordance with temperature
+ ∆Pp
*
*
∆Pp : correction in accordance with atmospheric pressure.
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