Basic Principle Of The Pressure Balance; Factors At Work; Local Fluctuations In The Gravity-Value - WIKA CPB 3000 Betriebsanleitung

Pressure Balance
CPB 3000

2.2 Basic principle of the Pressure Balance

Their operating principle is based on the physical definition of pressure, the quotient of force and
surface.
Force
essure =
Pr
Area
The key element of the pressure balance is a precision-manufactured piston/cylinder system with a
precisely measured cross-sectional surface.
To apply a pressure charge to the system, the piston is placed under a load with (calibrated) weight
pieces.
Each holding disk from the set of weights is identified by a nominal weight, which generates a
pressure value in the system (assuming standard reference conditions). Each weight has a number
and in the calibration certificate there is described the mass value to each weight with its resultant
pressure value. The weights are chosen according to the desired pressure value.
After that, the integrated spindle pump increases the pressure until the weights are in a floating state.

2.3 Factors at work

The piston pressure gauge is calibrated to standard reference conditions when it leaves the factory
(depending on customer specifications).
If there are significant deviations between the application conditions and the defined reference
conditions, appropriate corrections must be made.
Following are the main factors that enter into play and must be considered.
These corrections can be made automatically with the CalibratorUnit CPU 5000
(see accessories point 8)!

2.3.1 Local fluctuations in the gravity-value

The local force of gravitation is subject to major fluctuations caused by geographical variation.
The value may differ from one place on earth to another by as much as 0.5 %. Since this value has a
direct effect on the measurement, it is essential that it be taken into consideration.
The weight pieces can even be adjusted during manufacturing to match the location where they will be
used. Another option, especially if the device will be used at multiple locations, is to perform a
calibration to the standard gravity,
"Standard-g = 9.80665 m/s
Then a correction must be performed for each measurement according to the formula below:
=
True pressure Nominal
Example:
Local gravity set during manufacturing:
Locale gravity at application site:
Nominal pressure: 100 bar
=
p p
True pressure:
Nominal
Without the correction, measurements would all be "off" by 0.05 %.
WIKA Operating Instructions Pressure Balance Version 1.1
2
".
−
g Applicatio
⋅
value
S tan dard
9.806650 m/s
9.811053 m/s
g . 9
=
Local
100 bar
g . 9
S tan dard
n site
−
g
2
2
81105
=
100 . 0449 bar
80665
GB
.
.
.
7