2 Instruction Descriptions
2-396
NJ-series Instructions Reference Manual (W502)
The meanings of the variables that are used in this command are described below.
z Run (Execution Condition)
This is the execution condition for the instruction. PID control is performed while the value is TRUE.
PID control is stopped when the value changes to FALSE.
z ManCtl (Manual/Auto Control)
This instruction can be executed in one of two modes: Manual operation or automatic operation. The
value of ManCtl determines which mode is used.
z StartAT (Autotuning Execution Condition)
This is the execution condition for autotuning the PID constants. If the value of StartAT is TRUE
when the value of Run changes to TRUE, autotuning is performed when PID control is started. If the
value of StartAT changes to TRUE during PID control (i.e., when the value of Run is TRUE), autotun-
ing is performed during PID control. In either case, autotuning is canceled if the value of StartAT
changes to FALSE during autotuning. Autotuning is described in more detail later.
z PV (Process Value)
This is the process value of the controlled system.
z SP (Set Point)
This is the set point for the controlled system.
z MVLowLmt (MV Lower Limit) and MVUpLmt (MV Upper Limit)
You can limit the value of MV. MVLowLmt and MVUpLmt are the lower and upper limits to MV.
MVLowLmt must always be less than MVUpLmt.
If stop MV StopMV, error MV ErrorMV, or manual MV ManMV is set in manipulated variable MV, limit
control is not applied.
z ManResetVal (Manual Reset Value)
This is the value of MV when the deviation (i.e., the difference between PV and SP) is 0 for the pro-
portional action. The value of ManResetVal determines the location of the proportional action band.
z MVTrackSw (MV Tracking Switch)
MV tracking is a function that sets the MV to an external input value (called the MV tracking value)
during automatic operation. MV tracking is performed while the value of MVTrackSw is TRUE. When
the value of MVTrackSw changes to FALSE, the value of MV returns to the result of PID processing.
The value of MV is changed smoothly at this time (bumpless).
Meanings of Variables
Value of ManCtl Operation mode Value of MV
TRUE Manual Value of ManMV (PID control is not performed.)
FALSE Automatic Value that is calculated for PID control
MV from PID processing Value of MV
Less than MVLowLmt MvLowLmt
Between MVLowLmt and MVUpLmt, inclusive MV from PID processing
Greater than MVUpLmt MvUpLmt
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