red lion PXU10020, Instructions Manual

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Released 2018-01-12 Drawing No. LP0932
Auto-Tune Progress
The controller will oscillate the controlling output(s) for four cycles. The
AT annunciator will flash during this time. Parameter viewing is permitted
during Auto-Tune. The time to complete the Auto-Tune cycles is process
dependent. The controller should automatically stop Auto-Tune and store
the calculated values when the four cycles are complete. If the controller
remains in Auto-Tune unusually long, there may be a process problem.
Auto-Tune may be stopped by entering
NO
in
N
.
PID Adjustments
In some applications, it may be necessary to fine tune the Auto-Tune
calculated PID parameters. To do this, a chart recorder or data logging
device is needed to provide a visual means of analyzing the process.
Compare the actual process response to the PID response figures with
a step change to the process. Make changes to the PID parameters in
no more than 20% increments from the starting value and allow the
process sufficient time to stabilize before evaluating the effects of the
new parameter settings.
In some unusual cases, the Auto-Tune function may not yield
acceptable control results or induced oscillations may cause system
problems. In these applications, Manual Tuning is an alternative.
PROCESS RESPONSE EXTREMES
SP
TIME
INPUT
SLOW RESPONSE
TO QUICKEN RESPONSE:
- INCREASE OR DEFEAT SETPOINT RAMPING.
- EXTEND OUTPUT POWER LIMITS.
- DECREASE PROPORTIONAL BAND.
- DECREASE INTEGRAL TIME.
- DECREASE DERIVATIVE TIME.
MANUAL TUNING
A chart recorder or data logging device is necessary to measure the
time between process cycles. This procedure is an alternative to the
controller’s Auto-Tune function. It will not provide acceptable results if
system problems exist.
1. Set the Proportional Band (
ProP
) to 10.0% of the input range for
temperature inputs and 100.0% for process inputs.
2. Set both the Integral Time (
In
) and Derivative Time (
dr
) to 0
seconds.
3. Set the Output Cycle Time in Output Module
2-OP
to no higher than
one-tenth of the process time constant (when applicable).
4. Place the controller in Manual (
r
) Control Mode (
rnF
) and adjust the
% Power to drive the process value to the Setpoint value. Allow the
process to stabilize after setting the % Power. Note:
rnF
must be set
to
id
in Parameter Lockouts Module
3-LC
.
5. Place the controller in Automatic (
Auo
) Control Mode (
rnF
). Place the
value of % power into the Output Power Offset (
OPOF
). If the process will
not stabilize and starts to oscillate, set the Proportional Band two times
higher and go back to Step 4. Also put Output Power Offset (
OPOF
) back
to zero.
6. If the process is stable, decrease Proportional Band setting by two
times and change the Setpoint value a small amount to excite the
process. Continue with this step until the process oscillates in a
continuous nature.
7. Set the Proportional Band to three times the setting that caused the
oscillation in Step 6.
8. Set the Integral Time to two times the period of the oscillation.
9. Set the Derivative Time to 1/8 (0.125) of the Integral Time.
DIGITAL POTENTIOMETER
A PXU with an analog type Control Output 1 can be used as a digital
potentiometer. To use the PXU as a digital pot, configure the PXU for
Manual control mode. Also configure OP1 parameter to be displayed and
adjusted on display line 2. OP1 output terminals provide the analog
output (digital pot) signal. The OP1 parameter displayed on line 2 is
viewed in units of % output (0.0 to 100.0) only. If desired, the PXU line 1
display can be wired and configured to display the output signal level in
engineering units. To do this, wire the OP1 output signal (in series for
current signals and parallel for voltage signals) to the PXU’s input and
scale the input display for the desired Engineering units. For more
detailed information regarding using a PXU as a digital potentiometer,
see the “Digital Pot” Tech Note at www.redlion.net.
TIME
INPUT
Aut1 Aut4
AUTO-TUNE
START
SETPOINT
AUTO-TUNE COMPLETE, PID
SETTINGS ARE CALCULATED
AND LOADED INTO MEMORY
Aut2 Aut3
ON OFF ON OFF OUTPUT (r) :
PHASE
AUTO-TUNE OPERATION
(REVERSE ACTING)
TIME
SP
INPUT
OVERSHOOT AND OSCILLATIONS
TO DAMPEN RESPONSE:
- USE SETPOINT RAMPING.
- USE OUTPUT POWER LIMITS.
- INCREASE PROPORTIONAL BAND.
- INCREASE INTEGRAL TIME.
- INCREASE DERIVATIVE TIME.
- CHECK CYCLE TIME.