Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 367)

Chapter 26
PID Instruction
26–23
PID Tuning
PID tuning requires a knowledge of process control. If you are
inexperienced, it will be helpful if you obtain training on the process control
theory and methods used by your company.
There are a number of techniques that can be used to tune a PID loop. The
following PID tuning method is general, and is limited in terms of handling
load disturbances.
When tuning, changes should be made in the manual mode, followed by a
return to auto. Output limiting is applied in the manual mode.
Important: This method requires that the PID instruction controls a
non-critical application in terms of personal safety and
equipment damage.
The method requires only a few simple calculations.
Procedure
1. Create your ladder program. Make certain that you have properly scaled
your analog input to the range of the process variable PV and that you
have properly scaled your control variable CV to your analog output.
2. Connect your process control equipment to your analog modules.
Download your program to the processor. Leave the processor in the
program mode.
Important: Ensure that all possibilities of machine motion have been
considered with respect to personal safety and equipment
damage. It is possible that your output CV may swing between
0 and 100% while tuning.
3. Enter the following values: The initial setpoint SP value, a reset T
i
of 0, a
rate T
d
of 0, a gain K
c
of 1, and a loop update of 5.
Set the PID mode to STI or Timed, per your ladder diagram. If STI is
selected, ensure that the loop update time equals the STI time interval.
Enter the optional settings that apply (output limiting, output alarm, Smax
– Smin scaling, feedforward).
4. Get prepared to chart the CV, PV, analog input, or analog output as it
varies with time with respect to the setpoint SP value.
5. Place the PID instruction in the MANUAL mode, then place the
processor in the Run mode.
6. While monitoring the PID display, adjust the process manually by writing
to the CO percent value.
7. When you feel that you have the process under control manually, place
the PID instruction in the AUTO mode.