WIKA CPB5000HP - Handbuch (Seite 8)

Pressure Balance High-Pressure GB
CPB 5000 HP
WIKA Operating Instructions Pressure Balance High-Pressure Version 2.3 8
2.3.2 Temperature (Piston/Cylinder) .
The effective cross-sectional surface of the piston/cylinder system depends on the temperature.
The effect depends on the material used and is described by the temperature coefficient (TK).
In the event of deviations from standard reference conditions (typically 20°C), the following formula
must be used to make a correction:
( ) ( )
TK t t
pressure True
ference Appl
⋅ − +
⋅ =
Re
1
1
value Nominal
Example:
Reference temperature: 20°C
Temperature during use: 23°C
TK: 0.0022%
( )
( ) bar bar pressure True 99340 . 99
2 . 2 20 23 1
1
100
5
=
⋅ − +
⋅ =
−
Without the correction, measurements would all be "off" by 0.007 %.
2.3.3 Ambient conditions .
The effects of ambient conditions
air pressure
room temperature
relative humidity
should always be taken into consideration if the highest level of accuracy is required.
Fluctuations in ambient conditions change air density.
The air density affects the pressure through the buoyancy of the weights:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
− ⋅ =
density Weight
density Air
Weight 1 weight Nominal
The air density is typically 1.2 kg/m
3
The density of the weights (non-magnetic steel) is 7900 kg/m 3
A fluctuation of 5% in the relative humidity causes an additional uncertainty in the measurement of
about 0.001%.