Figure 90. Manual Cascade operation
Master Controller Slave setpoint
tracks slave
process variable.
Master output
t
racks slave
setpoint.
Slave output can
be
adjusted
manually.
Master setpoint
t
racks master
process variable.
Slave Controller
Cascade Operation in Auto Section 8 Operation Examples
206 3BUR002418-600 A
Meanwhile, the output of the master controller tracks a signal from the slave
controller which represents the setpoint of the slave automatically adjusted for ratio
or bias. The requirement for balancing the local and remote setpoint signals prior to
placing the slave controller in cascade mode is eliminated.
It may also be desirable for the setpoint of the master to track the master process
variable. This depends on the desirability of permitting the setpoint of the master to
vary indirectly in response to changes at the slave controller.
Cascade Operation in Auto
The cascade master is configured to permit only auto mode as the control element
(valve, air damper, etc.) is directly manipulated by the slave. The auto mode
simplifies operations by ensuring that all mode transfers and manual intervention
can be accomplished exclusively at the slave.
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