Process Control Instructions
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018 183
The function block is equipped with an internal tuner (modeler). The purpose of
the tuner is to identify the process model parameters and to use these parameters
as internal model parameters (gain, time constant, and deadtime). The tuner also
calculates an optimal response time constant. Set the tuner by configuring the
following parameters for each CV - PV process.
ProcessType Integral (level, position control) or nonintegrating (flow, pressure control)
ProcessGainSign Set to indicate a negative process gain (increase in output causes a decrease in PV); reset to
indicate a positive process gain (increase in output causes an increase in PV).
ResponseSpeed Slow, medium, or fast, based on control objective.
NoiseLevel An estimate of noise level on PV-low, medium, or high-such that the tuner can distinguish
which PV change is a random noise and which is caused by the CV step change.
StepSize A nonzero positive or negative number defining the magnitude of CV step change in either
positive or negative direction, respectively.
PVTuneLimit (only for integrating process type) in PV engineering units, defines how much of PV change
that is caused by CV change to tolerate before aborting the tuning test due to exceeding this
limit.
The tuner is started by setting the appropriate AtuneStart bit (AtuneCV1Start,
for example). You can stop the tuning by setting the appropriate AtuneAbort bit.
After the tuning is completed successfully, the GainTuned, TCTuned, DTTuned,
and RespTCTuned parameters are updated with the tuning results, and the
AtuneStatus code is set to indicate complete.
You can copy these parameters to the ModelGain, ModelTC, and ResponseTC,
respectively, by setting the AtuneUseModel bit. The control variable will
automatically initialize the internal variables and continue normal operation. It
will automatically reset the AtuneUseModel bit.
See also
CC Function Block Tuning Procedure on page 184
If an error occurs during the tuning procedure, the tuning is aborted, and an
appropriate AtuneStatus value is set. Also, a user can abort the tuning by setting
the AtuneAbort parameter.
After an abort, the CV will assume its value before the step change, and the
GainTu
ned, TCTuned, DTTuned, and RespTCTuned parameters are not
updated. The AtuneStatus parameter identifies the reason for the abort.
Tuning Errors
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