Siemens SIMATIC S7-200 System Manual page 403

To the right of the Chart Options region is a Legend that identifies the colors used to plot the PV,
SP, and Output values.
Directly beneath the Current PID
selection region is an area that is used to
display information pertinent to the
operation being performed.
The Advanced ... button in the Tuning
Parameters region allows you to further
configure parameters for the auto-tuning
process. The advanced screen is shown
below in Figure 15-3.
From the advanced screen you can
check the box that will cause the
auto-tuner to automatically determine the
values for the Hysteresis and Deviation
(default setting) or you can enter the
values for these fields that minimize the
disturbance to your process during the
auto-tune procedure.
In the Other Options region you can
specify the initial output step size and specify the initial output step size and
enter the zero crossing watchdog
timeout period.
In the Dynamic Response Options region click the radio button that corresponds to the type of
loop response that you wish to have for your process. Depending upon your process a fast
response may have overshoot and would correspond to an underdamped tuning condition. A
medium speed response may be on the verge of having overshoot and would correspond to a
critically damped tuning condition. A slow response may not have any overshoot and would
correspond to an overdamped tuning condition. A very slow response may not have overshoot
and would correspond to a heavily overdamped tuning condition.
Once you have made the desired selections, click OK to return to the main screen of the PID
Tuning Control Panel.
Once you have completed the auto-tune
sequence and have transferred the
suggested tuning parameters to the
PLC, you can use the control panel to
monitor your loop's response to a step
change in the setpoint. Figure 15-4
shows the loop's response to a setpoint
change (12000 to 14000) with the
original tuning parameters (before
running auto-tune).
Notice the overshoot and the long,
damped ringing behavior of the process
using the original tuning parameters.
PID Auto-Tune and the PID Tuning Control Panel
Figure 15-3 Advanced Parameters
Figure 15-4 Response to a Setpoint Change
Chapter 15
389