PPC3™ OPERATION AND MAINTENANCE MANUAL
© 2002-2007 DH Instruments, a Fluke Company Page 78
PRINCIPLE
A PPC3 or an RPM4 equipped with a Gxxx (gauge) or BGxxx (bi-directional
gauge) Q-RPT has a TEST(-) vent valve in its Q-RPT module (see Figure 13).
The TEST(-) vent valve connects the TEST(-) port to the VENT port which also
connects the Q-RPT and the device or system under test low side to
atmosphere. In normal PPC3 operation, the TEST(-) valve is closed
automatically whenever the PPC3 is performing fine pressure control to isolate
the TEST(-) circuit from fluctuations in ambient pressure. The valve is opened at
all other times. This assures that the pressure in the TEST(-) circuit does not
move too far away from atmospheric pressure as it might if it were permanently
shut off. In normal RPM4 operation as an external device to a PPC3, the TEST(-
) valve is normally closed. It is only opened when PPC3 is controlling with
coarse pressure control.
[SPECIAL], <7internal>, <5lo vnt> allows the TEST(-) vent valve to be set to be
permanently open, permanently closed or to operate in its default automated
condition. It also allows the current status of the valve to be viewed.
OPERATION
The normal setting for the TEST(-) vent valve is <1auto> in which PPC3
automatically controls the valve based on current PPC3 operation. Settings
other than <1auto> should only be selected by advanced users.
When the active Q-RPT is an external RPM4 Q-RPT, the Lo Vent operation
applies to the RPM4 Q-RPT module. The Lo Vent settings made from the
PPC3, apply only as long as the RPM4 is a PPC3 external device. When the
RPM4 power is cycled, the RPM4 Lo Vent will return to its original state.
To access the LO VNT function press [SPECIAL], <7internal>, <5lo vent>. If a Gxxx
(gauge) or BGxxx (bi-directional gauge) Q-RPT is not active, the display is:
<Available with Gxxx or BGxxx RPT only>.
If a Gxxx or BGxxx Q-RPT is active, the
display is:
Test(-) vent:1auto
2open 3close 4view
Select <1auto> for the TEST(-) vent valve operation to be controlled automatically
by PP3 based on current operation. This is the default and recommended setting.
Select <2open> to cause the TEST(-) valve to open and remain open regardless
of PPC3 operation until the setting is changed. If PPC3 detects a condition in
which it determines there could be a risk of overpressure to the RPT by opening
the TEST(-) vent valve, the message <Cannot open lo vent, DP overpressure
risk> is displayed. If this message is displayed, return to normal operation, vent
the PPC3 and try again.
Select <3close> to cause the TEST(-) valve to close and remain closed
regardless of PPC3 operation until the <lo vnt > setting is changed.
Select <4view> to view the current condition of the TEST(-) valve. The display
indicates whether current valve operation is controlled by the PPC3
(<Auto TEST(-) vent>) or has been set manually (<Manual TEST(-) vent>)
followed by the current valve status (<Open> or <Close>).
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