2 Instruction Descriptions
2-398
NJ-series Instructions Reference Manual (W502)
z DirOpr (Action Direction)
This variable specifies if MV is increased or decreased for changes in the value of PV. These are
called a forward action and a reverse action.
The difference between a forward action and reverse action are described here for temperature con-
trol. A forward action is used to control the MV for a cooler. That is, the higher the process tempera-
ture, the larger the MV of the cooler must be. On the other hand, a reverse action is used to control
the MV for a heater. That is, the lower the process temperature, the larger the MV of the heater must
be.
z ProportionalBand (Proportional Band)
This is one of the three PID constants. Refer to the description of the proportional action for details.
The larger the ProportionalBand is, the greater the offset is. Hunting occurs if the ProportionalBand
is too small.
z IntegrationTime (Integration Time)
This is one of the three PID constants. Refer to the description of the integral action for details. The
larger the value of IntegrationTime is, the weaker the integral action is.
z DerivativeTime (Derivative Time)
This is one of the three PID constants. Refer to the description of the derivative action for details.
The larger the value of DerivativeTime is, the stronger the derivative action is.
z ManMV (Manual Manipulated Variable)
MV is set to this value during manual operation (while ManCtl is TRUE). However, immediately after
changing from automatic to manual operation, the value of MV from automatic operation is used. MV
is set to the value of ManMV only when it changes after operation switches to manual operation.
When operation changes from manual to automatic operation, the value of MV from manual opera-
tion is used. The value of ManMV does not have to be between MVLowLmt and MVUpLmt.
Value of DirOpr Meaning Value of MV
TRUE Forward action Increases with the value of PV.
FALSE Reverse action Decrease with the value of PV.
MVUpLmt
MVLowLmt
MVUpLmt
MVLowLmt
PV
PV
MV
MV
Forward Action (DirOpr = TRUE)
Reverse Action (DirOpr = FALSE)
Cooler
The MV increases as the process temperature rises.
Heater
The MV increases as the process temperature falls.
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