Temperature (Piston/Cylinder); Ambient Conditions - WIKA CPB 3000 Betriebsanleitung

Pressure Balance
CPB 3000

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:
=
True pressure Nominal
Example:
Reference temperature: 20°C
Temperature during use: 23°C
TK: 0.0022%
=
True pressure 100
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:
=
Weight Nominal weight
The air density is typically 1.2 kg/m
The density of the weights (non-magnetic steel) is 7900 kg/m
A fluctuation of 5% in the relative humidity causes an additional uncertainty in the measurement of
about 0.001%.
WIKA Operating Instructions Pressure Balance Version 1.1
⋅
( (
value
+
1 t
Appl
1
⋅
(
bar
( )
+ − ⋅
1 23 20 2 2 .
⎛
Air density
⎜ ⎜
⋅ −
1
⎝
Weight density
3
1
) )
− ⋅
t TK
Re ference
=
)
99 . 99340 bar
−
5
⎞
⎟ ⎟
⎠
3
GB
.
.
8