Instructions
9.4 PID basic functions
PID control
Function Manual, 03/2017, A5E35300227-AC
473
Calculation of the parameters:
● PV_FAC = range of PV_NORM/range of CRP_IN;
● PV_OFFS = LL (PV_NORM) - PV_FAC * LL(CRP_IN);
where LL: Low limit
The scaling is switched off with the default values (PV_FAC = 1.0 and PV_OFFS = 0.0). The
effective process value is output at the PV output.
Note
With pulse control, the process val
ue must be transferred to the block in the fast pulse call
(reason: mean value filtering). Otherwise, the control quality can deteriorate.
Example of Process Value Scaling
If you want to enter the setpoint as a percentage, and you have a temperature range of -20
to 85 °C applied to , CRP_IN you must normalize the temperature range as a percentage.
The diagram below shows an example of adapting the temperature range -20 to 85 °C to an
internal scale of 0 to 100 %:
Forming the control deviation
The difference between the setpoint and process value is the control deviation before the
dead band.
The setpoint and process value must exist in the same unit.
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