Ny-Series Instructions Reference Manual (W560 - Omron NY532-5400 Reference Manual

2 Instruction Descriptions
Control Status and Manipulated Variable
Manipulated variable MV is determined according to the control status as shown in the following table.
Control status
Error end
MV tracking
during automatic
operation
Autotuning
during automatic
operation
Not autotuning
during automatic
operation
Instruction exe-
cution stopped
Manual opera-
tion
Autotuning
The 2-PID parameter α is not adjusted very often, so the main parameters that are adjusted for this
instruction are the PID constants. The PIDAT instruction supports autotuning of the PID constants. The
limit cycle method is used for autotuning. With the limit cycle method, the manipulated variable is tem-
porarily changed to the upper and lower limits of the manipulated variable to find the optimum PID con-
stants based on the resulting changes in the process value. If autotuning is executed when the set point
is greater than the process value, the manipulated variable is first set to the upper limit. When the devi-
ation reaches 0, the manipulated variable is set to the lower limit. When the deviation becomes greater
than the autotuning hysteresis, the manipulated variable is set to the upper limit again. This process is
repeated twice to calculate the optimum PID constants.
If autotuning is executed when the set point is less than the process value, the manipulated variable is
first set to the lower limit. Then, the optimum values for the PID constants are calculated with the proce-
dure that is given above.
2-676
Value of variable
ManCtl
Run (exe-
(man-
cution con-
ual/auto
dition)
control)
TRUE
FALSE
FALSE
TRUE ---
Error MVTrackSw
(error (MV tracking
end) switch)
TRUE ---
TRUE
FALSE
FALSE
---
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NY-series Instructions Reference Manual (W560)

Manipulated vari-
ATBusy
able MV
(autotun-
ing busy)
ErrorMV (error MV)
MVTrackVal (MV
FALSE
tracking value)
TRUE Value repeatedly
changes between
upper limit of MV
and lower limit of
MV.
FALSE Value calculated
with current PID
constants.
StopMV (Stop MV)
ManMV (manual
manipulated vari-
able)