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Process control instructions
Body
The standard function MOVE copies the value 16#8000 to the member Control of the DUT
PidParameters when the variable EnableAutoTuning turns from FALSE to TRUE (i.e. activates the
control mode auto-tuning in the function F355_PID_DUT).
The variables Set_Value_SP and Process_Value_PV are assigned to the members SP and PV of
the DUT PidParameters. They receive their values from the A/D converter channel 0 and 1.
Because the F355_PID_DUT function block has an EN output connected directly to the power rail,
the function is carried out when the PLC is in RUN mode. The calculated controller output stored by
the member MV of the DUT PidParameters is assigned to the variable Output_Value_MV. Its value
is returned via a D/A converter from the PLC to the output of the system.
LD
ST
When programming with structured text, enter the following:
(* Auto Tuning: *)
if
DF(EnableAutoTuning)
PidParameters.Control:=16#8000;
end_if;
(* Fill the DUT PidParameters with the corresponding input values: *)
PidParameters.SP:=Set_Value_SP;
PidParameters.PV:=Process_Value_PV;
(* Carry out the PID arithmetic: *)
F355_PID_DUT(PidParameters);
(* Write the manipulated value to the output: *)
Output_Value_MV:=PidParameters.MV;
944
then
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