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2.3 Cascade Control (Template 11)
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.
Profile Set Point
Local
Set Point
LSPt 1
Master PV Input
I/P1
Slave PV Input
I/P2
361 . 5
360. 0
Master
Deviation
888
PRG SEG
•1 With the Ramping Set Point function enabled (see Section 4.3, Set Points/ Ramp Rate), the
deviation bargraph shows the difference between the process variable and the actual (ramping)
set point value. The digital display shows the target set point value.
•2 Program selection can only be adjusted when the current program is stopped and program
selection is enabled – see Section 3.4/Profile Control/ Front Panel Program Select.
•3 Segments can only be skipped if a program is in Run or Hold mode and Segment Skip is enabled
– see Section 3.4/Profile Control/ Front Panel Skip Enable.
Slave Set
Point
S.SPt
Master
M.OP
MSPt
PID
Control Loop
MPV
M.OP x
CrtO + CbIA
SPV
Fig. 2.3 Cascade Controller
•1
2 OPERATOR LEVEL...
LOC
SSPt
Slave PID
Control Loop
CAS
Master Process Variable (MPV)
Master Control Set Point (MSPt)
['SPt.L' to 'SPt.H' – see Section 5.5]
Adjustable in local control only.
Local Set Point 1 is used for the profile set point and
is selected automatically when a profile is run.
Current Program/Segment
[1.01 to L.99 ]
X.NN
When the profile is in Run or Hold mode:
Press
to skip forward to the start of the next
segment.
Press
to skip back to the start of the current
segment.
When the profile is Stopped:
Press
or
be run.
Note. Only valid programs (i.e. those not
switched off) can be selected.
Continued on next page
Manual Output
Current Segment Number
Current Program Number
to select the profile program to
OP1
13
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