Using PID basic functions
7.3 TCONT_CP
PID control
236 Function Manual, 03/2017, A5E35300227-AC
Adjust the default factor (0.8) in the following situations, in particular:
● Process type I with PID (0.8 →0.6): Setpoint step changes within the control zone still lead
to approximately 18% overshoot with PFAC_SP = 0.8.
● Process type III with PID (0.8 →0.96): Setpoint step changes with PFAC_SP = 0.8 are
attenuated too strongly. This leads to a significantly slower response time.
Attenuation of control parameters
When a closed-loop control circuit oscillates or if overshoot occurs after setpoint step
changes, you can reduce the controller GAIN (e.g., to 80% of the original value) and
increase integral time TI (e.g., to 150% of the original value). If the analog output value of the
continuous controller is converted to binary actuating signals by a pulse shaper, quantization
noise may cause minor permanent oscillation. You can eliminate this by increasing the
controller deadband DEADB_W.
Modifying control parameters
Proceed as follows to modify control parameters:
1. Save the current parameters with SAVE_PAR.
2. Modify the parameters.
3. Test the control response.
If the new parameter settings are worse than the old ones, retrieve the old parameters with
UNDO_PAR.
Performing fine tuning manually
Requirements
● The instruction and the technology object have been loaded to the CPU.
To manually determine the optimal PID parameters, proceed as follows:
1. Click the "Start" icon.
If there is no online connection, this will be established. The current values for the
setpoint, process value and output value are recorded.
2. Select "Manual" from the "Mode" drop-down list.
3. Enter the new PID parameters.
4. Click on the icon
"Send parameter to CPU" in the "Tuning" group.
5. Select the "Change setpoint" check box in the "Current values" group.
6. Enter a new setpoint and click in the "Current Values" group on the icon
.
7. Clear the "Manual mode" check box.
The controller works with the new PID parameters and controls the new setpoint.
8. Check the quality of the PID parameter to check the curve points.
9. Repeat steps 3 to 8 until you are satisfied with the controller results.
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