DH Instruments PPCK PLUS, Operation And Maintenance Manual

Page: 52 / 150

PPCK+™ Operation and Maintenance Manual
©2001 DH Instruments, Inc .
Page 44
In dynamic control mode, whenever the pressure is Ready (inside the hold limit), the
display of measured pressure is equal to the target pressure. This is because in
dynamic control mode, when the pressure is
Ready , it is assumed that the measured
pressure equals the target pressure. This is not true when setting zero in absolute
measure mode (see Section 3.2.10.1).
A target pressure entry that exceeds the current upper limit (see Section 3.2.4) or
that is out of range will not be accepted as the target value when [ENTER] is pressed
and the buzzer will sound. The minimum and maximum in range target will be set.
See Section 6 if PPCK+ is unable to control pressure or appears to control
pressure poorly.
Pressing the [
←
] and [
→
] editing keys on the 4 x 4 keypad can be used while
controlling to jog the pressure control target value down or up by the current
hold limit. These keys also jog the target value when in the [SET P] screen (see
Section 3.2.11).
3.2.10.1 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] manual pressure control key
had been pressed (see Section 3.1.2.2). A Ready condition
occurs when the vent valve has been opened and the pressure
meets the current stability test.
Zero in
absolute
mode:
Since PPCK+ has no provision for setting pressure lower than
atmosphere, a command for automated pressure control to a
target value of zero when
absolute pressure measurement
mode is interpreted in the same way as a command for zero in
gauge measurement mode . PPCK+ executes the [VENT]
function (see Section 3.1.2.2) and a Ready condition occurs when
the vent valve has been opened and the pressure meets the
current stability test. The vented condition (atmospheric pressure)
is the lowest pressure that PPCK+ can set.
Due to the manner in which PPCK+ handles an automated pressure command for
zero in absolute pressure measurement mode, a Ready condition will occur at an
atmospheric pressure, not zero. When setting zero in absolute measurement
mode, the
Ready condition should not be interpreted to mean that the pressure is
zero within the hold limit. Ready is an indication that the PPCK+ TEST port is open
to atmospheric pressure and the rate of change of pressure has reached the
current stability limit. The current displayed pressure should be used as the
measured value of pressure applied to the device or system under test.