Fisher 4194B Series Instruction Manual page 34

4194A, B, and C Series
Fault
1. Process wanders or cycles about
set point
2. Controlling off set point as
reflected by process and set point
indicators.
Note: Some offset is inherent with
proportional only controllers (4194A
Series). The amount of offset is a
function of the proportional band
setting.
5–2
Table 5-1. Troubleshooting Chart
Possible Cause
1.1 Proportional band and reset
settings
1.2 Supply pressure varying
1.3 Process pointer rubbing on
cover or scale
1.4 Input element failure
1.5 Linkage failure
1.6 Relay malfunction
1.7 Anti-Reset Windup differential
relief valve set too low (suffix letter
F only)
2.1 Supply pressure not set
correctly
2.2 Linkage not connected
correctly.
2.3 Leak in input element/tubing
assembly.
2.4 Indicators out of calibration.
2.5 Flapper not aligned.
2.6 Leak in feedback system.
Check
1.1 Refer to the Start-up section for
controller settings.
1.2 Monitor the supply pressure
with an external gauge. Ensure that
it is set correctly and does not
fluctuate. Note the number of
instruments being supplied by the
regulator.
1.3 Note if the pointer is bent.
1.4 Inspect the element for loose
screws and damaged flexures,
links or pivots. Using a soap
solution, check the sensing
element for leaks.
1.5 Check for links bent or not
connected properly, flexures bent
or broken, pivots broken.
1.6 By changing the process
differential pressure and observing
the output, verify that the output
moves at about the same speed in
both directions.
1.7 The minimum relief valve
setting is dependent on the loop
dynamics and the controller
settings if, under normal load
changes the relief valve opens,
instability can occur. Check by
observing the controller reaction to
a set point or load change under
closed loop conditions.
2.1 Check with an external source.
2.2 Inspect for loose screws and
damaged flexures, links or pivots.
2.3 Using soap solution, check the
input element and tubing for leaks.
2.4 Refer to the process indicator
and remote set point (if applicable)
zero and span calibration
procedures in section 3 or 4.
2.5 Refer to the Flapper alignment
procedures in section 3 or 4.
2.6 Open the reset valve to .01
minutes/repeat. Adjust output
pressure to 20 psig (1.4 bar). Using
soap solution, check for leaks in
the proportional and reset bellows
and in the tubing that connects
these bellows.
–Continued–
Correction
1.1 If stable control cannot be
attained, and all other elements of
the loop are functionally correct,
examine other possible causes
related to the controller.
1.2 Correct as necessary. One
regulator per instrument is
recommended.
1.3 Bend pointer to provide
clearance.
1.4 Repair or replace parts as
necessary.
1.5 Replace or repair as necessary.
1.6 If the output moves fast in one
direction and sluggishly in the
other, replace the relay.
1.7 If the anti-reset windup
differential relief valve appears to
be set too low, perform the
anti-reset windup calibration
procedures in section 4.
2.1 Reset the supply pressure if
necessary. If the condition occurs
again, rebuild or replace the
regulator.
2.2 Repair or replace parts as
necessary.
2.3 Repair or replace parts as
necessary.
2.4 Adjust as necessary.
2.5 Align the flapper as necessary.
2.6 Repair as necessary.