Fluke 2470 specifications K2 = 1/ g1 1 − ρa / ρb, For SI Units

		Explanation of "Pressure Calculation Worksheet"	A
		Introduction
For SI Units:		K2 = 1/ [g1 (1 − ρa / ρb )]
where:
g	=	acceleration due to local gravity in m/sec2
1
ρ air	=	density of air in g/cm3; see Equation A-4
ρ am	=	density of apparent mass;
		for Apparent Mass versus Brass, 8.4 g/cm3
		for Apparent Mass versus Stainless Steel, 8.0 g/cm3

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 K1 or K2 values.

The apparent mass (Column 9) is obtained from:

	M A = F K2
where:
M A =	apparent mass versus brass; record in Column 9

F= force required on piston; as found in Column 8

K2 = multiplier which was obtained by previous equation

When the masses are applied to the piston in an evacuated bell jar, the above equations for K1 and K2 can still be used. In this situation, the density of air ( ρ air ) 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, PB , 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, PH , 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.

A-3