Instructions
9.1 PID_Compact
PID control
Function Manual, 03/2017, A5E35300227-AC
251
Sampling time of the PID algorithm
The controlled system needs a certain amount of time to respond to changes in the output
value. It is therefore not advisable to calculate the output value in every cycle. The sampling
time of the PID algorithm represents the time between two calculations of the output value. It
is calculated during tuning and rounded to a multiple of the cycle time. All other functions of
PID_Compact are executed at every call.
If you use Output_PWM, the accuracy of the output signal is determined by the ratio of the
PID algorithm sampling time to the cycle time of the OB. The cycle time should be at least 10
times the PID algorithm sampling time.
An increase of the output value is generally intended to cause an increase in the process
value. This is referred to as a normal control logic. For cooling and discharge control
systems, it may be necessary to invert the control logic. PID_Compact does not work with
negative proportional gain. If InvertControl = TRUE, an increasing control deviation causes a
reduction in the output value. The control logic is also taken into account during pretuning
and fine tuning.
Input parameters of PID_Compact V2
Table 9- 1 Input parameters of PID_Compact V2
Setpoint of the PID controller in automatic mode
Input REAL 0.0 A tag of the user program is used as source for the
process value.
If you are using parameter Input, then Con-
fig.InputPerOn = FALSE must be set.
Input_PER INT 0 An analog input is used as the source of the process
value.
If you are using parameter Input_PER, then Con-
fig.InputPerOn = TRUE must be set.
Disturbance variable or precontrol value
ManualEnable BOOL FALSE
• A FALSE -> TRUE edge activates "manual mode",
while State = 4, Mode remains unchanged.
As long as ManualEnable = TRUE, you cannot
change the operating mode via a rising edge at
ModeActivate or use the commissioning dialog.
• A TRUE -> FALSE edge activates the operating
mode that is specified by Mode.
We recommend that you change the operating mode
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