ABB C505 User Manual page 28

...2 OPERATOR LEVEL
2.8 Cascade with Feedforward (Template 13)
For cascade control, two internally-linked PID controllers are used, with the first (master) PID
controller providing the set point for the second (slave) controller. The feedforward disturbance
variable signal is added to the master output (slave set point). The disturbance signal is weighted by
the feedforward gain (FFGn) and the feedforward bias (FFbs) values.
Local Set Point
LSPt
MSPt
Master PV Input
MPV
I/P1
Feedforward Disturbance Variable
I/P3
Slave PV Input
SPV
I/P2
Master
•1
Set Point
(MSPt)
MST
Master
Process
Variable
(MPV)
OP1
Slave
Set Point
(SSPt)
SLV
Slave
Process
Variable
(SPV)
OP1
•1 With the Ramping Set Point function enabled (see Section 3.3, Set Points/ Ramp Rate), the
bargraph shows the actual (ramping) set point value and the digital display shows the target set point
value.
24
Local Slave
Set Point
SSPt
Master
M.OP x
PID
CrtO + CbiA
Control Loop
DV x FFGn + FFbS
Fig. 2.7 Cascade Controller with Feedforward
450. 2
500. 0
•1
70
1997
2000
70
L L R
SSPt
∑
FFGn
= 0
Master Process Variable (MPV)
Master Control Set Point (MSPt)
['SPLO' to 'SPHI' – see Section 4.5]
Adjustable in Local control only
Slave Control Output
[0 to 100% (–10 to 110% for analog outputs)]
Adjustable in Manual mode only.
Slave Process Variable (SPV)
Slave Set Point (SSPt)
['SPLO' to 'SPHI' – see Section 4.5]
Adjustable in Manual mode only
Note. The key can be used in this frame to
L L R
change between cascade and local slave set points.
Continued...
Manual
Output
Slave
PID
Control Loop
OP1