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Explanation of Pressure Calculation Worksheet
(Pages A9 and A11)
These tables may be used with gas and hydraulic piston pressure gauges that are operated
with an atmospheric reference or vacuum reference.
piston reference gauge level,
P
and
is the head pressure created by the pressure medium and the difference in height
H
between the piston pressure gauge and the device under test.
A. A minimum of six significant figures must be used in all calculations involving
reported constants, masses, etc. The manufacturer's claims for accuracy assume the
local gravity to be known to at least six significant figures
B. When the piston pressure gauge is used as a standard of pressure, it is convenient to
perform the pressure-to-mass calculations in advance of operating the standard. Since
the piston gauge temperature fluctuates while it is operated, a confusing point in the
procedure is the necessity for the temperature of the gauge to be predicted prior to
operation. This "expected temperature" however is used to allow the pressure
calculations to be performed. Once the piston pressure gauge is floating at the
intended pressure, a final temperature observation is made and then "trim" masses are
loaded onto the piston gauge to correct for any temperature variations that exist
between the expected and the actual temperatures. The final column in the worksheet
is used to calculate the temperature coefficient, which defines the amount of trim that
is required to correct for this temperature change.
It is usually prudent to select an expected temperature
temperature that will be experienced. This is so that the operator can always add mass
to correct for the actual temperature. Adding mass is generally more convenient than
subtracting mass from the planned loading arrangement. Standard metric trim mass
set is entirely suitable for this purpose.
P
represents the pressure desired at the device under test,
B
Appendix A
Calculations
P
represents the pressure at the
A
( )
t
, which is lower than any
A-1
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