Fluke RUSKA 2470 - Manual (Page 61)

Explanation of "Pressure Calculation Worksheet"
Introduction
A
A-3
For SI Units
:
( ) [ ]
b a
g K
ρ ρ
/ 1 / 1
1 2
− =
where:
1
g = acceleration due to local gravity in m/sec 2
air
ρ
= density of air in g/cm 3 ; see Equation A-4
am
ρ
= density of apparent mass;
for Apparent Mass versus Brass, 8.4 g/cm 3
for Apparent Mass versus Stainless Steel, 8.0 g/cm 3
When selecting masses from the calibration report, assure that the values selected are in the same
Apparent Mass unit of measure that was used to calculate the
1
K or
2
K values.
The apparent mass (Column 9) is obtained from:
2
K F M
A
=
where:
A
M = apparent mass versus brass; record in Column 9
F = force required on piston; as found in Column 8
2
K = multiplier which was obtained by previous equation
When the masses are applied to the piston in an evacuated bell jar, the above equations for
1
K
and
2
K can still be used. In this situation, the density of air (
air
ρ ) will be zero which will cause
the buoyancy portion of the equation to become 1. Also, the results will indicate the quantity of
true mass (not apparent mass) that must be applied to the piston.
E. Column 1,
B
P , is the desired pressure at the reference plane of the device being calibrated.
F. Column 2 is the mass density of the pressure medium being used in the piston pressure gauge
system. For hydraulic piston pressure gauges, this number can be considered constant for
all pressures. RUSKA Instrument has two types of hydraulic piston fluids available. One is
a Spinesstic 22 ™ part number 55-500 which has a density of 0.031 pounds per cubic inch
(858 kilograms per cubic meter). The other is a Dioctyl Sebacate (DOS) part number
55-521-1 which has a density of 0.033 pounds per cubic inch (913 kilograms per cubic meter).
For gas medium piston gauges, the values in Column 2 will be different for different system
pressures. Equations are provided to calculate the density of air or nitrogen as a function of
the system pressure.
G. Column 3 is required to adjust the mass density of the pressure medium for local gravity. It is
also used to correct the pressure head that exist between the reference ports of the piston
gauge and device under test.
H. Column 4,
H
P , is the pressure correction that is required if the reference plane of the device
being calibrated is not the same plane as the reference plane of the piston pressure gauge.
The difference between the two planes, h, is positive if the reference plane of the device
being calibrated is higher than the reference plane of the piston pressure gauge.