The PID parameters are displayed in the "PID Parameters" configuration window. The PID parameters will be adapted to your controlled system during controller tuning. You do not need to enter the PID parameters manually.
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Note The currently active PID parameters are located for PID_Compact V1 in the sRet structure and as of PID_Compact V2 in the Retain.CtrlParams structure. Change the currently active PID parameters only in "Inactive" mode online to prevent malfunction of the PID controller. If you want to change the PID parameters in "Automatic mode" or "Manual mode" online, change the PID parameters as follows:
Online changes to the PID parameters in "Automatic mode" can result in jumps at the output value. |
The PID algorithm operates according to the following equation:
|
Symbol |
Description |
|
y |
Output value of the PID algorithm |
|
Kp |
Proportional gain |
|
s |
Laplace operator |
|
b |
Proportional action weighting |
|
w |
Setpoint |
|
x |
Process value |
|
TI |
Integration time |
|
a |
Derivative delay coefficient (derivative delay T1 = a × TD) |
|
TD |
Derivative action time |
|
c |
Derivative action weighting |
The diagram below illustrates the integration of the parameters into the PID algorithm:
All PID parameters are retentive. If you enter the PID parameters manually, you must completely download PID_Compact.
Downloading technology objects to device
Proportional gain
The value specifies the proportional gain of the controller. PID_Compact does not work with a negative proportional gain. Control logic is inverted under Basic settings > Controller type.
Integration time
The integration time determines the time behavior of the integral action. The integral action is deactivated with integration time = 0.0. When the integration time is changed from a different value to 0.0 online in "Automatic mode", the previous integral action is deleted and the output value jumps.
Derivative action time
The derivative action time determines the time behavior of the derivative action. Derivative action is deactivated with derivative action time = 0.0.
Derivative delay coefficient
The derivative delay coefficient delays the effect of the derivative action.
Derivative delay = derivative action time × derivative delay coefficient
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0.0: Derivative action is effective for one cycle only and therefore almost not effective.
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0.5: This value has proved useful in practice for controlled systems with one dominant time constant.
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> 1.0: The greater the coefficient, the longer the effect of the derivative action is delayed.
Proportional action weighting
The proportional action may weaken with changes to the setpoint.
Values from 0.0 to 1.0 are applicable.
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1.0: Proportional action for setpoint change is fully effective
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0.0: Proportional action for setpoint change is not effective
The proportional action is always fully effective when the process value is changed.
Derivative action weighting
The derivative action may weaken with changes to the setpoint.
Values from 0.0 to 1.0 are applicable.
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1.0: Derivative action is fully effective upon setpoint change
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0.0: Derivative action is not effective upon setpoint change
The derivative action is always fully effective when the process value is changed.
PID algorithm sampling time
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 sampling time of the PID algorithm is used as the period duration of the pulse width modulation. The accuracy of the output signal is determined by the ratio of the PID algorithm sampling time to the cycle time of the OB. It is therefore recommended that the cycle time is a maximum of one tenth of the PID algorithm sampling time.
Rule for tuning
Select whether PI or PID parameters are to be calculated in the "Controller structure" drop-down list.
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PID
Calculates PID parameters during pretuning and fine tuning.
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PI
Calculates PI parameters during pretuning and fine tuning.
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User-defined
The drop-down list displays "User-defined" if you have configured different controller structures for pretuning and fine tuning via a user program.