LSPt
M.SPt
L
L
R
I/P1
I/P2
OP1
Master Process Variable Input
Slave Process Variable Input
M.PV
Master
PID
Control Loop
Set Point
Ramp
DV
I/P3
Feedforward Disturbance Variable
M.OP
S.SPt
S.PV
•1
•1 The feedforward signal can be multiplied by the control output (instead of added) using the PC configurator
•2 Feedforward operation is disabled by setting '
FFGN
' to '
OFF
'
Local Set Point
•2
FFGn = 0FF
Profile
Set Point
Manual Output
Slave
PID
Control Loop
Slave Set Point
M.PV–
M.SPt
∑
DV x FFGn + FFbS
M.OP x C.rtO + C.bIA
PV–
CSPt
A6 Cascade Controller with Feedforward (Template 13)
Note. This template cannot be used for heat/cool or boundless control
Cascade with Feedforward Control. Two PID controllers are implemented within the COMMANDER 350 with the first (master) controller
providing the set point for the second (slave) controller. The two controllers are linked internally. To the master output (sla
ve set point) a feedforward
signal is added. This signal is a disturbance variable which is weighted by the feedforward gain (
FFGn
) and the feedforward bias (
FFbs
) values.
When the auto/manual mode is changed (from the front panel or by a digital signal) both the master and slave controllers change
mode. In manual
the slave set point can be adjusted by the user and the value is tracked by the master controller (taking account of the feedfo
rward signal) to ensure
bumpless transfer back into auto. The slave can also be taken out of cascade mode using the front panel
To Next Page
Loading...
