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24
350.0
351.5
70
Master
Deviation
OP1
•1
207.0
207.0
70
OP1
MST
SLV
Slave
Deviation
…2
OPERATOR LEVEL
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.
Fig. 2.6 Cascade Controller
Master Process Variable (M.PV)
Master Control Set Point (MSPt)
['SPLO' to 'SPHI' – see Section 5.5]
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
L
L
R
key can be used
to change between local/remote set point values.
Slave Process Variable (S.PV)
Slave Set Point (S.SPt)
['SPLO' to 'SPHI' – see Section 5.5]
Adjustable in manual or local slave set point modes
only.
Note. The
L
L
R
key can be used in this frame to
change between cascade ( R symbol is lit) and
local slave set points.
Continued…
•1 With the Ramping Set Point function enabled (see Section 4.3, Set Points/ Ramp Rate), the
bargraph shows the actual deviation (PV/Ramping Set Point value). The digital display shows
the target set point value.
RSPt
M.SPt
I/P3
I/P1
I/P2
OP1
Local
Set Point
Remote Set Point
input
Master PV Input
Slave PV Input
Slave Set
Point
Slave PID
Control Loop
M.PV
Master
PID
Control Loop
•1
•1 Template 12 Only
LSPt
SSPt
L
L
R
Manual Output
RSPt x
rAtO
+
bIAS
M.OP x
CrtO
+
CbIA
L
L
R
S.SPt
M.OP
Profile Set Point