DH Instruments PPC2+, Manual

Page: 58 / 166

PPC2+™ Operation and Maintenance Manual
©2001 DH Instruments, Inc.
Page 50
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PRINCIPLE
The PPC2+ exhaust (down) control valves and the output of the exhaust pressure
regulator are connected to the PPC2+ EXHAUST port (see Section 5.8.1.7).
The response of the pneumatic module used to control pressure, particularly when
controlling pressure near and under atmospheric pressure, changes depending on
whether the EXHAUST port is connected to a vacuum source or left open to atmosphere.
To use the proper pressure control algorithms, PPC2+ must know the condition of the
exhaust port.
The ControlRef function allows the PPC2+ to know whether its exhaust port is at vacuum
or atmospheric pressure. An independent exhaust pressure sensor measures the
pressure present at the EXHAUST port. Normally, the exhaust sensor output is used
automatically by PPC2+ to determine the exhaust port condition. If desired, this automatic
determination can be overridden and the exhaust port condition set manually.
The ControlRef function allows setting of whether the EXHAUST port condition will be
determined automatically using the exhaust sensor or set manually. It also allows viewing
of the current status of the EXHAUST port.
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OPERATION
To access the ControlRef function, press [SETUP],
and select <1ControlRef>. The display is:
Make the appropriate selection.
Selecting <1auto> sets the PPC2+ to determine the EXHAUST port condition
automatically using its internal exhaust sensor. This is the normal control ref setting.
Selecting <2vac> sets the PPC2+ to assume that a vacuum supply is connected to the
EXHAUST port.
Selecting <3atm> sets the PPC2+ to assume that the EXHAUST port is open to
atmospheric pressure.
2vac 3atm 4view