RUSKA 2470
Users Manual
All of the calculations will be performed to this expected temperature ( t ). A final trim would be calculated to adjust the piston gauge to the temperature of the piston at the time of the actual measurement. This correction is calculated in the last column of the worksheet. This column represents the number of grams to be added to the stack of masses for a difference in the actual temperature from the expected temperature, ( t ). The final trim is computed using the following formula and loaded onto the piston gauge;
“Temp. Coef.” x (actual temperature – expected temperature)”
C.The Symbol Ao(t ) represents the effective area of the piston and its cylinder at atmospheric pressure, when operating at temperature ( t ); it is obtained from the relation
Ao(t ) = Ao(23) (1 + c Δt)
where:
Ao(23) = reported area of the piston at 23 degrees Celsius
c= thermal coefficient of superficial expansion
Δt = ( t − 23)
D.Gravity and Buoyancy Correction: When the masses are applied to the piston in the presence of the buoyant atmosphere, buoyancy corrections are necessary and are combined with gravity corrections. For convenience, the combined correction K1 (or K2) is applied as a multiplier with the result indicating the quantity of apparent mass that is required to produce the desired force (F) on the piston.
For English Units
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| K1 = (gs / g1 ) [ ρ am /(ρ am − ρ air )] |
where: |
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gs | = | acceleration due to standard gravity, 980.665 cm/sec2 |
g | = | acceleration due to local gravity in cm/sec2 |
1 |
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ρ air | = | density of air in g/cm3; see Equation |
ρ am | = | density of apparent mass; |
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| for Apparent Mass versus Brass, 8.4 g/cm3 |
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| 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 K1
where:
M A = apparent mass; record in Column 9
F= force required on piston; as found in Column 8
K1 = | multiplier which was determined by previous equation |
