Instructions
9.3 PID_Temp
PID control
Function Manual, 03/2017, A5E35300227-AC
383
Mode of operation of PID_Temp
Monitoring process value limits
You specify the high limit and low limit of the process value in the Config.InputUpperLimit
and Config.InputLowerLimit tags. If the process value is outside these limits, an error occurs
(ErrorBits = 0000001h).
You specify a high and low warning limit of the process value in the
Config.InputUpperWarning and Config.InputLowerWarning tags. If the process value is
outside these warning limits, a warning occurs (Warning = 0000040h), and the
InputWarning_H or InputWarning_L output parameter changes to TRUE.
You specify a high limit and low limit of the setpoint in the Config.SetpointUpperLimit and
Config.SetpointLowerLimit tags. PID_Temp automatically limits the setpoint to the process
value limits. You can limit the setpoint to a smaller area. PID_Temp checks whether this area
is within the process value limits. If the setpoint is outside these limits, the high or low limit is
used as the setpoint, and output parameter SetpointLimit_H or SetpointLimit_L is set to
TRUE.
The setpoint is limited in all operating modes.
You can specify a substitute setpoint at the SubstituteSetpoint tag and activate it with
SubstituteSetpointOn = TRUE. In this way, you can temporarily specify the setpoint directly,
for example for a slave controller in a cascade, without having to change the user program.
The limits set for the setpoint also apply to the substitute setpoint.
With the default setting, PID_Temp only uses the outputs for heating (OutputHeat,
OutputHeat_PWM, OutputHeat_PER). The output value of the PID algorithm
(PidOutputSum) is scaled and output at the outputs for heating. You specify with
Config.Output.Heat.Select if OutputHeat_PWM or OutputHeat_PER is calculated.
OutputHeat is always calculated.
With Config.ActivateCooling = TRUE, you can also activate the outputs for cooling
(OutputCool, OutputCool_PWM, OutputCool_PER). Positive output values of the PID
algorithm (PidOutputSum) are scaled and output at the outputs for heating. Negative output
values of the PID algorithm are scaled and output at the outputs for cooling. You specify with
Config.Output.Cool.Select if OutputCool_PWM or OutputCool_PER is calculated. OutputCool
is always calculated.
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