Technology instructions
10.2 PID control
S7-1200 Programmable controller
588 System Manual, V4.2, 09/2016, A5E02486680-AK
STEP 7 provides the following PID instructions for the S7-1200 CPU:
● The PID_Compact instruction is used to control technical processes with continuous
input- and output variables.
● The PID_3Step instruction is used to control motor-actuated devices, such as valves that
require discrete signals for open- and close actuation.
● The PID_Temp instruction provides a universal PID controller that allows handling of the
specific requirements of temperature control.
hanges that you make to the PID configuration and download in RUN do not take effect
until the CPU transitions from STOP to RUN mode. Changes that you make in the "PID
parameters" dialog using the "Start value control" take effect immediately.
All three PID instructions (PID_Compact, PID_3Step, and PID_Temp) can calculate the P-, I-
, and D-components during startup (if configured for "pre-tuning"). You can also configure
the instruction for "fine tuning" to allow you to optimize the parameters. You do not need to
manually determine the parameters.
Note
Execute the PID instruction at constant intervals of the sampling time (preferably in a cyclic
OB).
Because the PID loop needs a certain time to respond to changes of the control value, do
not calculate
the output value in every cycle. Do not execute the PID instruction in the main
program cycle OB (such as OB
1).
The sampling time of the PID algorithm represents the time between two calculations of the
output value (control value). The output value is calculated during self-tuning and rounded to
a multiple of the cycle time. All other functions of PID instruction are executed at every call.
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