Instructions
9.3 PID_Temp
PID control
Function Manual, 03/2017, A5E35300227-AC
387
Monitoring signal validity
The values of the following parameters are monitored for validity when used:
● Setpoint
● SubstituteSetpoint
● Input
● Input_PER
● Disturbance
● ManualValue
● SubstituteOutput
● PID parameters in the structures Retain.CtrlParams.Heat and Retain.CtrlParams.Cool.
Monitoring the sampling time PID_Temp
Ideally, the sampling time is equivalent to the cycle time of the cyclic interrupt OB. The
PID_Temp instruction measures the time interval between two calls. This is the current
sampling time. On every switchover of operating mode and during the initial startup, the
mean value is formed from the first 10 sampling times. Too great a difference between the
current sampling time and this mean value triggers an error (Error = 0000800h).
The error occurs during tuning if:
● New mean value >= 1.1 x old mean value
● New mean value <= 0.9 x old mean value
The error occurs in automatic mode if:
● New mean value >= 1.5 x old mean value
● New mean value <= 0.5 x old mean value
If you deactivate the sampling time monitoring (CycleTime.EnMonitoring = FALSE), you can
also call PID_Temp in OB1. You must then accept a lower control quality due to the
deviating sampling time.
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