PPC2+™ Operation and Maintenance Manual
©2001 DH Instruments, Inc.
Page 32
Automated Pressure Commands for Zero Pressure
Zero in
gauge
mode:
A command for automated pressure control to a target value of
zero when in gauge pressure measurement mode is interpreted
in the same manner as if the [VENT] direct pressure control key
had been pressed (see Section 3.1.2.2). A Ready (<*>) condition
will occur when the vent valve has been opened and the pressure
meets the current stability test.
Zero in
absolute
mode:
When attempting to set a target pressure of zero in absolute
measurement mode, PPC2+ opens its down control valves fully
and closes a bypass interrupt valve to interrupt the natural flow of
gas out the EXHAUST port through its pressure regulators once
pressure is under 3.5 psia (25 kPa). However, even with a vacuum
pump connected to its EXHAUST port, there is a limit to how low
the pressure in PPC2+ can be pulled down. This is a function of
the quality of the vacuum pump used, the characteristics of the
volume connected to the TEST port and PPC2+’s internal
restrictions. When a command for automated pressure control to a
target value of zero is given when in absolute pressure
measurement mode, PPC2+ responds by reducing the pressure
as far as possible using down fast pressure control. A Ready (<*>)
condition will be indicated when the stability limit is reached and the
control down fast valve will remain open keeping the vacuum pump
connected to the PPC2+ pneumatic module and TEST port. When
pressure control is suspended or a non-zero pressure target is
executed, the bypass interrupt valve is opened.
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Summary of Contents for PPC2+
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