DH Instruments FPG8601, Руководство по эксплуатации и обслуживанию

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7. PISTON-CYLINDER MAINTENANCE
Page 117 © 2007 DH Instruments, a Fluke Company
7.8 DETERMINING EFFECTIVE AREA
There are several ways to determine the effective area of the FPG piston-cylinder. The two most common
ways are to cross float with another piston gauge and to compare using a high accuracy null indicator. Since
DHI
determines the effective area of the FPG by cross floating with a PG7000, this section focuses on the
cross float procedure with a piston gauge.
For the best results, determine the effective area in gauge mode. There is added uncertainty caused by
measuring the residual vacuum of the FPG and a piston gauge in absolute mode. In addition, the testing time
is significantly increased due to the time required to achieve a vacuum at each piston gauge mass load.
Performing a cross float in absolute mode is still valid and recommended for comparison to gauge mode only.
It is recommended that at least 5 test pressures distributed throughout the 15kPa span of the FPG be used
when cross floating the FPG. Each point should be repeated 3 times to make sure that proper leak rate
adjustment is achieved.
7.8.1 SETTING UP THE SYSTEM
Set up the piston gauge and the FPG for operation in gauge mode. Make sure that the
FPG has an isolation valve connected to the test port on the upper left side of the
mounting post.
Using FPG Tools, create a DUT that is the reference piston gauge and activate it (see
Section 5.5). If a
DHI
PG7000 is the reference piston gauge, remote operation is
recommended. Use the
[Run w/Point Log]
menu choice to enable data acquisition. It is
important that the FPG pressure is averaged at each test point. Select kPa as the
pressure unit to simplify the effective area calculations.
Obtain a static pressure controller (ex. MPC1) that will allow generation of pressures up
to 15kPa.
It is important that a common atmospheric reference is used between the piston gauge
and the FPG. Connect the atmospheric reference of the piston gauge to the lower
mounting post of the FPG. In Figure 63 the PG is connected to the output of valve 9.
This connection is used for convenience only. The output of valve 9 is a KF25 fitting so
an adaptor is not necessary.
Connect a low flow metering valve to the FPG manifold control isolation port as indicated
in the diagram. Adjust the metering valve approximately 1/4 turn from fully closed.
The valve is used to compensate for the lubrication flow of the FPG at each test
pressure. Without the metering valve, the lubrication flow will increase the FPG pressure
relative to the piston gauge and cause the piston gauge piston to continually rise.
Figure 63.
FPG8601 and PG7000 Cross Float Setup