General Piston Pressure Gauge Considerations | 2 |
Measurement of Pressure with the Piston Pressure Gauge |
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Figure 2-5. Head Correction Measurement
PH = (Pm − PAIR )* h * g
Where:
his the vertical distance between the reference plane of the Standard and the reference plane of the DUT (Device Under Test)
ρair | is the density of the air |
ρm | is the density of the test media |
gis the acceleration due to local gravity
L1 is the vertical distance from the mass loading location to the effective bottom of the piston.
Dis the vertical distance from the mass loading location to the bottom of the Hanger Mass
Note
For instances where the reference plane of the DUT is LOWER than the reference plane of the standard, the h is a negative number and therefore
PH becomes a negative number.
In addition, gas lubricated piston pressure gauge calculations should account for the fact that the pressure gradient mentioned in the preceding paragraph changes as system pressure is changed. This is because the specific gravity of gas varies as a function of pressure, not remaining approximately constant, as does a hydraulic fluid.
