L33354-XA28UEN-E1-S01, REV. A CLOSED-LOOP TUNING
Copyright © 2020 Amatrol, Inc.
S01-10
SKILL 1 TUNE A CONTROL LOOP USING THE AUTO-TUNE METHOD
11. Perform the following substeps to evaluate the response using the auto-tuned PID values.
NOTE
For a process in a plant or factory, before you adjust PID values, verify that no mechanical issues are causing the
less than desirable results. For example, if the controller increases its output steadily, but the PV does not respond
for a while, but then makes a large jump, you should suspect a valve that is sticking and releasing. Also, if the
controller output for a steady state is above 90% or below 10%, then suspect the valve is not sized correctly. No
amount of PID fine tuning will correct these mechanical issues.
A. Determine the desired outcome for this process.
This sounds too obvious, but it is important. Is speed the most important or is stability the most important? Does
the process need to arrive at SP as quickly as possible and overshoot with diminishing oscillations is acceptable?
Does the process need to operate at a stable PV during variable conditions and oscillations are undesirable? Your
instructor may decide to make up arbitrary conditions for you.
B. Determine if the process is currently too fast and too unstable.
If you determine it is too unstable, the proper correction depends on the cause of the instability.
•If the proportional band is set too low, try doubling the present value.
•If the integral time is set too short, try multiplying the time by two or three.
•If the derivative is set too low, then increase it or eliminate it by setting it to zero. Derivative is not really needed
in a level process. A derivative that is set way too long can cause oscillations.
C. Determine if the process is currently too slow and sluggish.
If you determine it is too sluggish, the proper correction depends on the cause of the sluggishness.
•If the proportional band is set too wide, try cutting in half the present value.
•If the integral time is set too long, try decreasing the time. If you go too short a time, it will cause oscillations.
•If the derivative is set too high, then decrease it or eliminate it by setting it to zero.
D. Write down your proposed new PID values to try below.
It may be that the auto-tuned values gave acceptable results. If so, you would be done. However, you might
try some slightly different values to see if you can improve the response a little. Be prepared to explain to your
instructor why you think your new values may be better.
P _______________________________________________________________________________________
I ________________________________________________________________________________________
D _______________________________________________________________________________________
E. Repeat step 10 and record the results on a new graph.
Determine if the new values produced a better response than the auto-tuned values. For a process in a plant, you
may need several adjustments over a period of days before you reach the ideal PID values.
12. Perform the following substeps to shut down the 990-PC1.
A. Place PB1 in the OFF position (out).
This stops the circulation pump.
B. Place PB2 in the OFF position (out).
This closes the solenoid drain valve SV 100C (SV3).
C. Open (fully counterclockwise) the process tank’s right manual drain valve, HV 100C (HV4), to drain the right side
of the tank. Leave the left drain valve, HV 300 (HV3), closed. When the right side of the tank is empty, close (fully
clockwise), the right drain valve.
The water should remain in the left side of the process tank.
D. Turn off the main circuit breaker.
E. Disconnect the control circuit.
