PPC2 AF OPERATION AND MAINTENANCE MANUAL
© 1998 DH Instruments, Inc. Page 122
SYMPTOM POSSIBLE CAUSE SOLUTION
Will not set pressure.
Pressure and/or vacuum supply
incorrectly connected or not adequate.
Correct pressure and/or vacuum
supply (2.3.3, 2.3.4).
Disagreement between Hi and Lo
reference transducer or between
transducer ranges appears excessive.
Difference is actually in tolerance and
represents “natural” disagreement..
Compare differences observed to
tolerances on reference transducer
measurements (1.3.2)
Disagreement between
measurements made by different
ranges at the same pressure is not
zero but an autozero routine was just
executed.
Readings by different ranges at the
same pressure can disagree even
after a valid autozero.
Check that disagreement between
ranges is within tolerance (1.3.2, 5.2).
Will not set pressure. Target exceeds UL range. Check UL (3.2.4) and range (3.2.1).
Will not set pressure.
There is a very large leak in the test
system or TEST port is not connected.
Correct leak.
Poor pressure control at low
pressures.
ControlRef not properly set to reflect
pressure conditions at EXHAUST port.
Set ControlRef properly (3.3.1).
Poor pressure control at pressures
under atmosphere or inability to reach
pressures under atmosphere.
Vacuum supply is incorrectly
connected, is not low enough or is
unstable.
Correct vacuum supply (2.3.4, 3.3.1).
Poor pressure control characterized
by "hunting" around target.
Pneumatic control module needs to be
reconfigured.
Reconfigure control module (5.1.1)
Poor pressure control characterized
by control stopping completely near
the target pressure.
Control mode is set to static rather
than dynamic.
Set control mode to dynamic (3.1.2.3,
3.2.3)
There is a restriction in the test
connection between the PPC2 AF and
the test.
Remove the restriction to allow free
flow between the PPC2 AF and the
test.
Poor pressure control characterized
by excessive overshooting and/or
undershooting, inability to "lock-on"
target.
A filter in the PPC2 AF, the SPLT or an
accessory is dirty and causing a restriction.
Clean and dry or replace the filter
element (5.1.3).
Poor pressure control characterized
by excessive pressure noise at control
point and/or hunting around target.
Excessive leak present in system.
Correct internal or external leak (3.2.8,
5.1.2).
Poor pressure control characterized
by minor overshooting.
Some overshooting is part of normal
operation to speed up operation.
Check whether overshooting is within
normal limits (3.1.2.3).
Poor pressure control characterized
by very slow slew rate.
Test volume is beyond normal limits.
Reduce test volume if slew rate is
unacceptable (1.3.3)
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