Allen-Bradley Logix5000

530 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 13 Special Instructions (FBC, DDT, DTR, PID)
PID Theory
The following figures show the process flow for PID instructions.
PID Process
PID Process with Master/Slave Loops
+
-
-1
+
SP
Displayed
as EUs
Error
Displayed
as EUs
Software A/M
or
A/M Station Mode
Control
Action
Auto
SP-PV
(Error)
Manual
No
Yes
PVT
SP
PV-SP
Converts Binary to
Engineering Units
(PV-mini)(maxs-mins)
+ mins
maxi-mini
PV
PV
Displayed
as EUs
Converts Units
to %
Error X 100
maxs-mins
PID
Calculation
Output
Bias %
Software A/M
Mode
Auto
Auto(Out%)
Set
Output %
Converts Tieback Units
to %
tieback-mintie
maxtie-mintie
x 100
Manual
Manual
Output
Limiting
Set
Output %
A/M Station
Mode
Output (CV)
Displayed as %
of EU Scale
Convert % to CV Units
CV%(maxcv-mincv)
100
+ mincv
CV
+
-
-1
+
+
-
-1
+
SP
Auto
Manual
PVT
No
Yes
Converts Binary to
Engineering Units
(PV-mini)(maxs-mins)
maxi-mini
+ mins
PV
SP-PV
PV-SP
(Error)
Converts Units
to %
Error X 100
maxs-mins
PID
Calculation
Output
Bias %
Software A/M
Mode
Auto
Auto(Out%)
Output
Limiting
Set
Output %
A/M Station
Mode
Set
Output %
Manual
Manual
(Master.Out)
SP
PV
Master
Loop
Software A/M
or
A/M Station Mode
Control
Action
Slave
Loop
(Master.Out)
Converts Binary to
Engineering Units
(PV-mini)(maxs-mins)
maxi-mini
+ mins
(SP)
PV
Converts % to
Engineering Units
Converts Tieback Units
to %
tieback-mintie
maxtie-mintie
x 100
Converts Units
to %
Error X 100
maxs-mins
Converts Units
to %
Error X 100
maxs-mins
X (maxs-mins)
100
+ mins
Control
Action
SP-PV
PV-SP
PID
Calculation
Output
Bias %
Set
Output %
Auto
Auto
Manual
Manual
A/M Station
Mode
Output
Limiting
Software A/M
Mode
Set
Output %
Convert % to CV Units
CV%(maxcv-mincv)
100
+ mincv
Items referenced in this box are
parameters, units, and modes as they
pertain to the designated Slave loop.
Manual
Manual
Auto
Software A/
M Mode