Pid Theory; Pid Process; Pid Process With Master/Slave Loops - Allen-Bradley Logix5000 Reference Manual

Chapter 13 Special Instructions (FBC, DDT, DTR, PID)

PID Theory

SP
Displayed
as EUs
Software A/M
or
A/M Station Mode
SP-PV
Auto
+
-
SP
Manual
-1
PVT
No
Yes
Converts Binary to
Engineering Units
(PV-mini)(maxs-mins) + mins
maxi-mini
PV
Master
Loop
Software A/M
or
A/M Station Mode
Auto
SP-PV
+
-
SP
Manual -1
PVT
No
Yes
Converts Binary to
Engineering Units
(PV-mini)(maxs-mins)
+ mins
maxi-mini
PV
Slave
Loop
Converts % to
(SP)
(Master.Out) Engineering Units
X (maxs-mins)
+ mins
100
Converts Binary to
Engineering Units
(PV-mini)(maxs-mins)
maxi-mini
530
The following figures show the process flow for PID instructions.

PID Process

Error
Displayed
as EUs
Control
Action
Converts Units
(Error)
to %
PID
Calculation
Error X 100
PV-SP maxs-mins
PV
Displayed
as EUs
Converts Tieback Units

PID Process with Master/Slave Loops

Control
Action
Converts Units
(Error)
to %
PID
Calculation
Error X 100
PV-SP
maxs-mins
Set
Output %
Converts Units
SP
to %
Error X 100
PV
maxs-mins
Control
Action
SP-PV
Converts Units
to %
+
-
Error X 100
-1
PV-SP maxs-mins
+ mins
Converts Tieback Units
PV
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Output
Bias %
Software A/M
Mode
(Out%) Auto
+
Auto
Manual
Manual
Set
Output %
to %
tieback-mintie
x 100
maxtie-mintie
Output
Bias %
Software A/M
Mode
A/M Station
Mode
(Out%) Auto
+
Auto
Output
Manual
Limiting
Manual
Software A/
M Mode
Auto
Manual
Manual
Items referenced in this box are
parameters, units, and modes as they
pertain to the designated Slave loop.
Output
Bias %
Software A/M
Mode
A/M Station
Auto
PID
+
Calculation
Auto
Manual
Set
Manual
Output %
to %
tieback-mintie
x 100
maxtie-mintie
Set
Output %
A/M Station
Mode
Convert % to CV Units
Output
CV%(maxcv-mincv)
Limiting
+ mincv
100
Output (CV)
Displayed as %
of EU Scale
Set
Output %
(Master.Out)
Set
Output %
Mode
Convert % to CV Units
Output
Limiting
CV%(maxcv-mincv)
+ mincv
100
CV