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Tune Mode Operation 3.4
Proportional output control 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.
3.4.1 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 certian 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(s) 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, if used) at the factory
default settings. Obtain the best possible process reaction by adjusting the Proportional
Bandwidth 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 70).
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 with the best possible proportional band adjustment)
Manual Reset may be added to eliminate this offset.
8. Auto Reset may be added to eliminate offsets and improve response to setpoint and load
changes. 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.
9. If necessary, Rate may be added. Rate is a dynamic tuning parameter. Rate may be
required to compensate for process lags or to help inhibit reset windup when a large
amount of Auto Reset (4 or 5 repeats per 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.
