102BTechnology instructions
9.2 PID control
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
339
Table 9- 19 Sample configuration settings for the PID_3Step instruction
Settings
Description
Controller type
Selects the engineering units.
Invert the control logic Allows selection of a reverse-acting PID loop.
If not selected, the PID loop is in direct-acting mode, and the output of PID loop
increases if the input value < setpoint).
If selected, the output of the PID loop increases if the input value > setpoint.
Enable last mode after
CPU restart
Restarts the PID loop after it is reset or if an input limit has been exceeded and
returned to the valid range.
Input
Selects either the Input parameter or the Input_PER parameter (for analog) for the
process value. Input_PER can come directly from an analog input module.
Output
Selects either to use the digital outputs (Output_UP and Output_DN) or to use the
analog output (Output_PER) for the output value.
Basic
Feedback
Selects the type of device status returned to the PID loop:
No feedback (default)
Feedback
Feedback_PER
Process
value
Scales both the range and the limits for the process value. If the process value goes below the low limit or
above the high limit, the PID loop goes to inactive mode and sets the output value to 0.
To use Input_PER, you must scale the analog process value (input value).
Motor transition
time
Sets the time from open to close for the valve. (Locate this value on the data sheet or
the faceplate of the valve.)
Minimum ON time Sets the minimum movement time for the valve. (Locate this value on the data sheet or
the faceplate of the valve.)
Minimum OFF
time
Sets the minimum pause time for the valve. (Locate this value on the data sheet or the
faceplate of the valve.)
Error behavior
Defines the behavior of the valve when an error is detected or when the PID loop is
reset. If you select to use a substitute position, enter the "Safety position". For analog
feedback or analog output, select a value between the upper or lower limit for the
output. For digital outputs, you can choose only 0% (off) or 100% (on).
Actuator
Scale Position
Feedback
1
"High stop" and "Lower limit stop" define the maximum positive position (full-open)
and the maximum negative position (full-closed). "High stop" must be greater than
"Lower limit stop".
"High limit process value" and "Low limit process value" define the upper and lower
positions of the valve during tuning and automatic mode.
"FeedbackPER" ("Low" and "High") defines the analog feedback of the valve
position. "FeedbackPER High" must be greater than "FeedbackPER Low".
1
"Scale Position Feedback" is editable only if you enabled "Feedback" in the "Basic" settings.