West Control Solutions MRC 7000 Controller Manual - Manual (Page 42)

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Tune Mode Operation 4.3
Proportional output controllers may require the adjustment (tuning) of the PID and other
related parameters. This provides a means for the instrument's control algorithm to be
adjusted to meet specific application requirements.
4.3.1 SYSTEMATIC TUNING METHOD
1. Changes in tuning parameters should be made one at a time.
2. After making any changes in tuning parameters, a disturbance should be introduced into
the process so that the process reaction may be observed. This process reaction, or
recovery, will tell whether the tuning parameters provide the desired control. It is usually
easiest to make a step change in setpoint to introduce this disturbance.
3. The change in setpoint or disturbance, referenced above should be large enough to cause
an observable deviation of process from setpoint. However, this change should not be so
large that it will cause the controller output to proceed to either extreme limit.
4. Controller tuning for optimal control is not hard and fast, BE PATIENT: The process will
take a certain amount of time to react to the setpoint changes during tuning. The amount
of time depends upon the specific process, however, a period of 8 to 12 minutes should
be allowed between changes. The important point to remember is to allow the process to
react completely, do not rush through tuning of the controller. If the complete process
reaction is not observed, optimum control may never be achieved.
5. Time Proportioning control output(s) require the cycle time to be adjusted for the
application. Short cycle times typically result in the most accurate process control, but will
cause the quickest "wear out" of any mechanical components.
6. Leave all other tuning parameters (except for the alarm settings) at the factory default
settings. Obtain the best possible process reaction by adjusting the Proportional Band
width parameter. The setting that achieves the best response for the process should be
left in the controller programming, and should be noted on the Software Reference Sheet
in Appendix E (page 72).
7. If there are to be no setpoint or load changes in the process, the Proportional Band
adjustment may be all that is necessary for proper control. If an offset still exists (the
process does not settle out at setpoint for the best possible proportional band adjustment),
Manual Reset may be added to eliminate this offset.
8. Auto Reset may be added to eliminate process offsets with respect to setpoint. Increase
Auto Reset from 0 to 0.2 increments. Start with a small amount. Increase this increment if
there is no apparent reaction. Remember to allow the process 8 to 12 minutes to react to
any changes.
9. If necessary, Rate may be added. Rate is a dynamic tuning parameter. Rate may be
required to compensate for load changes or to inhibit process oscillations that occur when
a large amount of auto reset (4 or 5 repeats/minute) is being used.
10. Controller tuning is not hard and fast. It may be necessary to adjust the tuning
parameters over a period of time to obtain optimal control of the process.