ControlMaster CM30 and CM50
Universal process controllers,
1
/4 and
1
/2 DIN 8 Templates and Functionality
IM/CM/ED–EN Rev. B 69
8.3.3 Cascade with Feedforward
This template connects 2 PID loops together in order to enhance the control of a Master variable (loop) by
manipulation of a slave loop. The first (master) controller provides the set point for the second (slave)
Controller. The 2 controllers are linked internally.
To the Master output a feedforward signal is added. This signal is a disturbance variable which is weighted
by the feedforward ratio and bias values. . When the auto/manual mode is changed via the front panel or by
a digital signal both the master and slave controllers change mode, the slave setpoint can then be adjusted
from the front panel, and this value is then tracked by the Master controller (taking account of the
feedforward signal) to ensure a bumpless transfer back into auto mode.
8.3.4 Ratio Controller (Internal / External Ratio)
The ratio controller template configures the ControlMaster to regulate one process variable against another
based on a specified ratio. The unregulated variable or 'wild' variable is weighted by ratio and bias values
and this forms the control setpoint for the process variable. The ratio value applied to the wild variable can
either be a local value set on the front panel or a remote signal on an analog input.
A/M
DV
L/R
MSP
AIN 1
AIN 2
x Ratio
+ Bias
LSPT1
LSPT2
LSPT3
LSPT4
Local
Set Point
Local
Set Point
Loop 1 PID
Control (Master)
PID
O/P
2
OP
Time Prop
Output
Motorized
Valve
Split
Output
AO1
RLY1
RLY2
RLY1
OP2
OP1
Output Type
Analog
Output
Manual
Output
MPV
SSP
LR
SPV
Loop 2
PID
Control
(Slave)
AIN 4
AIN 3*
x FF Gain
*Source can be changed in Control / FeedForward configuration – see Section 7.4, page 36
RSP
PID
PID
O/P 1
AIN 1
AIN 2
AIN 3
Local
Ratio
Manual
Output
A/M
OP
PID
O/P
Loop1
PID Control
PV
S
P
Analog
Output
Output Type
AO1
PV – Bias
WV
WV
WV x Ratio
+ Bias
A
c
t
u
a
l
R
a
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