ABB C505 User Manual page 25

2.7 Cascade Control (Templates 11 and 12)
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 master output is weighted
using the cascade ratio (C.rtO) and bias (C.bIA) values to create the slave set point value.
Local
Set Point
LSPt
Remote Set Point
input
RSPt x
•1
I/P3
RSPt
rAtO + bIAS
Master PV Input
MPV
I/P1
Slave PV Input
I/P2
•1 Template 12 Only
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.
L
L R
Master
M.OP
PID
Control Loop
M.OP x
CrtO + CbIA
SPV
Fig. 2.6 Cascade Controller
450. 2
500. 0
•1
70
450. 2
500. 0
70
Slave Set
Point
L
L R
SSPt
SSPt
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.
Note. With template 12 the
to change between local/remote set point values.
Slave Process Variable (SPV)
Slave Set Point (SSPt)
['SPLO' to 'SPHI' – see Section 4.5]
Adjustable in manual or local slave set point modes
only.
Note. The
change between cascade and local slave set points.
Continued...
2 OPERATOR LEVEL...
Manual Output
Slave PID
Control Loop
key can be used
L L R
key can be used in this frame to
L L R
OP1
21