IMC Function Block Tuning
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.
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 variable. |
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 AtuneStart bit. You can stop the tuning by setting the 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 function block will automatically initialize the internal variables and continue normal operation. It will automatically reset the AtuneUseModel bit.
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