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4194A, B, and C Series
the system again by changing the set point. Continue
this procedure until the system cycles. At this point,
double the proportional band setting (proportional
band setting
2).
Tuning reset action: Disturb the system. If the sys-
tem does not cycle, speed up the reset by changing
the setting to a lower value (faster reset). Disturb the
system again. Continue this procedure until the sys-
tem cycles. When the system cycles, multiply the re-
set time setting by a factor of three (reset setting
and slow down the reset by changing the reset setting
to the higher value. The reset is now tuned.
Tuning rate action: For a controller with rate (4194C
Series), adjust the rate toward the higher setting until
cycling occurs. When the system cycles, divide the
rate value by a factor of three (rate setting 3) and
decrease the rate by changing the setting to the lower
value. The rate is now tuned.
7. Check the stability of the recommended proportion-
al band settings by introducing a disturbance and
monitoring the process.
8. Once stable control is attained, the process pointer
and set point indicator should be in line. If they are
aligned, adjust the set point to the desired value. If
they are not, readjust the set point to the desired con-
trol point and proceed with step 9.
9. If the process pointer is within 5 percent of the set
point indicator, turn the link 3 adjustment (see figure
5-13 for location) until the process pointer aligns with
the set point indicator. Turn the link 3 adjustment
screw clockwise to increase the process indication or
counterclockwise to decrease it. If the process pointer
is misaligned with the set point indicator by more than
5 percent of the scale span, perform the calibration
procedures for 4194B and C Series controllers.
Calibration of 4194B and C Series
Controllers
General Calibration Instructions
If the controller has the auto/manual sta-
tion (suffix letter E), be sure the control-
ler is in the automatic mode before per-
forming calibration.
If the prestartup checks, or startup, reveal faulty con-
troller operation, perform the calibration described in
this section. These instructions are valid for either
shop or field calibration, provided that open process
loop conditions exist. Unless otherwise noted, key
numbers are found in figure 5-21.
4–4
Note
Do not use the gauges supplied with the controller dur-
ing calibration. Monitor process pressure, supply pres-
sure, controller output pressure, and, if applicable, re-
mote set point pressure with external gauges.
Process Indicator Zero and Span
Calibration
Before starting this procedure:
3)
Provide a regulated process differential pressure
to the controller and a means of measurement exter-
nal to the controller.
Provide a means of measuring the controller out-
put pressure by connecting the controller output to a
pressure gauge (open-loop conditions must exist).
Provide a regulated supply pressure to the controller.
Do not exceed the normal operating pressure in table
1-4.
Any change to the process pointer span
adjustment will require readjustment of
the process pointer zero adjustment.
Refer to figures 4-1 and 4-3 for adjustment locations.
1. Remove the two screws (key 6) and lift off the pro-
portional band indicator cover (key 36).
2. Set the proportional band between DIRECT and
REVERSE.
3. Apply process differential pressure equal to the
process scale span lower limit.
4. The process pointer should indicate the process
scale lower limit. If not, adjust the process pointer to
the process scale lower limit by loosening the zero
adjustment locking screw and turning the zero adjust-
ment screw. Tighten the zero adjustment locking
screw.
5. Apply process differential pressure equal to the
process scale span upper limit.
6. The process pointer should indicate the process
scale upper limit. If not, adjust the span screw to cor-
rect one-half the error as follows: clockwise to in-
crease span for a low indication (below the upper lim-
it); counterclockwise to decrease span for a high
indication (above the upper limit).
7. Repeat steps 3 through 6 until the error is elimi-
nated.
8. Apply process differential pressure equal to the
mid-scale value on the process scale span. The pro-
cess pointer should indicate the mid-scale mark, 2
percent of span. If the error is greater than 2 percent,
refer to the Maintenance section and perform the zero
and span adjustment procedure.
Note
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