Technology instructions
10.2 PID control
S7-1200 Programmable controller
596 System Manual, V4.2, 09/2016, A5E02486680-AK
PID_Compact instruction Process value limits
"Process value limits" are normally used in conjunction with the analog input; however, you
can use them for other purposes.
The Process value limits configuration serves two functions:
● Sets the upper and lower limits for the Setpoint High/Low alarm outputs on the PID block
● Sets a limit so that the process variable cannot exceed or go below those limits
regardless of the setpoint. This configuration defines fixed limits for the process.
On the PID block, you can use four alarm outputs:
● SetpointLimit_H: Setpoint exceeds the High Limit.
● SetpointLimit_L: Setpoint exceeds the Low Limit.
● InputWarning_H: Process Variable exceeds the input high limit.
● InputWarning_L: Process Variable exceeds the input low limit.
When you set the Process value limits, the points that trigger the Setpoint high and low
alarm outputs to go true are set to the same value. For example, with the settings shown
above, if you enter a setpoint that is greater than 120%, the "SetpointLimit_H" output goes
true. This action is the same for the low limit. If you enter a setpoint that is lower than 0%,
then the "SetpointLimit_L" goes true. This gives your program an indication that the entered
setpoint is out-of-range. This alarm can prompt you to re-enter the setpoint.
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