DH Instruments PPCK PLUS, Operation And Maintenance Manual

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PPCK+™ Operation and Maintenance Manual
©2001 DH Instruments, Inc .
Page 22
3.1.2.4 AUTOMATED PRESSURE CONTROL MODES
PPCK+ automated pressure control provides automated adjustment and control of
pressure to a user designated target value. This feature allows pressure values to
be set precisely by simple numerical entry. Pressing
[SET P] from the main run
screen allows a pressure control target value to be entered and executed.
Pressing [ESCAPE] or a manual pressure control key causes active pressure control
to be interrupted (see Section 3.1.2.2).
PPCK+ supports two pressure control modes to meet different pressure setting and
controlling requirements. The two control modes are designated
static and
dynamic . Pressure control parameters for each control mode are automatically set
to optimal default values for each PPCK+ range when the control mode is selected
in the active range (see Sections 3.2.1, 3.2.3). If desired, control parameters can be
customized by the user using the CUSTOM CONTROL function (see Section 3.2.6).
Control parameters:
•
Target Value: The pressure setpoint specified by the operator.
•
Hold Limit: A symmetrical positive and negative limit around the target value
within which the controlled pressure is to be maintained.
•
Stability Limit: A rate of change of pressure limit in units of pressure/second
used as a criterion for the Ready/Not Ready condition in static control or when
automated control is not active.
See STATIC CONTROL and DYNAMIC CONTROL in this section for a detailed
explanation of each control mode and its advantages, the default control parameters
and the Custom Control options. See Table 4 for a summary of the two
control modes.
Table 4. Static and Dynamic Pressure Control Modes Summary
CONTROL
MODE ADVANTAGES DISADVANTAGES BEST USED
Static
•
Control error can be
completely
eliminated.
•
Minimizes pressure
setting time ( Ready
to Ready ).
•
Provides maximum
tolerance for leaks in
test volume.
•
May require
averaging of DUT
readings for best
results.
•
When testing
multiple DUTs, final
pressure is not
exactly the same for
each DUT at a set
point.
•
Set pressure is not
equal to target
pressure.
•
When data
acquisition from the
DUT is automated
allowing averaging
of the DUT
readings.
•
When minimizing
uncertainty is a
priority.
•
When reducing
pressure setting time
is a priority.
Dynamic
•
Set pressure is equal
to target pressure.
•
When testing
multiple DUTs, final
pressure is the same
for all DUTs at each
set point.
•
Control error is
added to
measurement
uncertainty.
•
Increases pressure
setting time ( Ready
to Ready ).
•
Limited tolerance of
leaks in test volume.
•
When DUT readings
must be recorded
manually.
•
When it is
imperative that the
final pressure be
equal to the set
pressure requested.