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RUSKA 2465A-754
Users Manual
A-2
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
( )
t o
A
represents the effective area of the piston and its cylinder at
atmospheric pressure, when operating at temperature
( )
t
; it is obtained from the
relation
( ) ( )
( )
t c A A
o t o
Δ + =
1
23
where:
( )
23 o
A
= reported area of the piston at 23 degrees Celsius
c
= thermal coefficient of superficial expansion
t
Δ
=
( )
23
−
t
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
1
K
(or
2
K
) 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
( ) ( )
[ ]
air am am s
g g K
ρ ρ ρ
− =
/ /
1 1
where:
s
g
= acceleration due to standard gravity, 980.665 cm/sec
2
1
g
= acceleration due to local gravity in cm/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.