DH Instruments PPC3 - Interrupting Automated Pressure Control; Automated Pressure Commands for Zero Pressure

PPC3™ OPERATION AND MAINTENANCE MANUAL
© 2002-2007 DH Instruments, a Fluke Company Page 48
For PPC3 to set pressures under atmosphere and/or to reliably set pressures under
20 kPa (3 psi) gauge other than zero gauge, a vacuum pump must be connected to the
EXHAUST port (see Section 2.3.6) and PPC3 must be set up for control using a vacuum
reference (see Section 3.5.7.2). Setting zero gauge pressure does not require a vacuum.
The [ ] and [ ] direct pressure control keys can be used while controlling to jog the
pressure control target value up or down by the jog step value (see Section 3.1.3).
These keys also jog the target value when in the ENTER target value screen.
3.3.10.1 INTERRUPTING AUTOMATED PRESSURE CONTROL
Automated pressure control is interrupted by:
• Pressing [ESC]: Suspends control and remains in MAIN RUN screen.
Does not vent pressure. PPC3 passively measures the pressure applied to
its TEST(+) port.
• Pressing any direct pressure control key other than the jog keys (see
Section 3.1.3): Suspends control and executes direct pressure control.
• Pressing any function key: Suspends control and goes to the selected
function. Does not vent pressure. PPC3 passively measures the pressure.
• Pressing [ENT/SET P]: Suspends control and goes to ENTER target
pressure value screen. Does not vent pressure. PPC3 passively measures the
pressure applied to its TEST(+) port.
To resume automated pressure control, press [ENT/SET P] and ENTER a target pressure
value.
3.3.10.2 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 or negative gauge measurement mode is interpreted in the same
manner as if the [VENT] direct pressure control key had been pressed
(see Section 3.1.3). A Ready condition occurs when the vent sequence has
completed, including running AutoZ if applicable (see Section 3.5.1).
Zero in
absolute
mode:
In response to a command for automatic pressure control to a target value of
zero when in absolute measurement mode, PPC3 opens its down control valves
fully to the EXHAUST port allowing the vacuum source connected to the
EXHAUST port to pull down the pressure as far as possible (see Figure 12). The
down valves stay open until another pressure command is given or control is
aborted. In addition, on all PPC3 controllers except PPC3-A10M, a bypass is
closed to interrupt the natural flow of gas out the EXHAUST port through the
pneumatic module pressure regulators. How low the pressure in the PPC3 and
the system connected to the PPC3 TEST(+) will go is a function of the quality of the
vacuum pump used, the characteristics of the volume connected to the TEST(+)
port and PPC3’s internal restrictions.
A Ready condition occurs when the pressure control stability limit is reached (see
Section 3.2.2).