PPC2 AF OPERATION AND MAINTENANCE MANUAL
© 1998 DH Instruments, Inc. Page 28
3.2.3.1.2 Automated Pressure Commands for Zero Pressure
Zero in gauge mode:
A command for automated pressure control 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:
Even with a vacuum pump connected to its reference EXHAUST,
PPC2 AF cannot set absolute zero pressure due to internal
restrictions and the continuous gas flow through its EXHAUST port.
When a command for automated pressure control of zero when in
absolute pressure measurement mode is given, PPC2 AF 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 with the control down fast remaining open.
Due to the manner in which PPC2 AF handles an automated pressure
command for zero in absolute pressure measurement mode, a ready
condition can occur at a pressure well outside of the hold limit. When setting
zero in absolute measurement mode, the "ready" condition should not be
used as an indication that the pressure is zero. "Ready" is an indication that
the PPC2 AF has reduced the pressure as far as possible and that the
pressure is now stable. The current displayed pressure should be used as
the value of pressure applied to the device or system under test.
3.2.4 UPPER LIMIT
PURPOSE
To set the upper limit pressure value for a pressure range.
PRINCIPLE
The UPPER LIMIT function provides the capability to enter a maximum pressure not to be
exceeded when using a specific range. Automated pressure control target values above the
upper limit will not be accepted and direct pressure control keys will shut off when the upper
limit is reached.
The UPPER LIMIT function is most often used to protect the device or system that the
PPC2 AF is testing from accidental overpressure.
If no upper limit value is entered by the user, the upper limit for each range is set by
default to 105 % of the active range for ranges L3 and H3 and to 115 % of the active range
for all other ranges.
OPERATION
When the UPPER LIMIT function key is pressed from the main run screen the display is:
1. Entry field to enter desired upper limit value.
RngH3 upper limit
1050 psi a
Enter the desired upper limit value and PPC2 AF returns to main run screen with new upper
limit value active.
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