Figure 91. Auto Cascade Operation
Master Controller Remote slave
setpoint tracks
master output.
Local setpoint on
Master
.
Slave Controller
Section 8 Operation Examples Cascade Operation in Auto
3BUR002418-600 A 207
• The slave setpoint tracks (automatically remains equal to) the slave process
variable while in manual. This feature eliminates the need for the slave to
respond immediately to any deviation when the mode is changed from manual
to auto (cascade). Without setpoint tracking, the response to any deviation
would be to ramp the slave output at the reset rate.
• The output of the master tracks the setpoi
nt of the slave while the slave is in
manual. This ensures that the local (slave) setpoint and remote setpoint (master
output) are in balance prior to placing the slave loop in cascade (auto) mode.
• The setpoint of the master tracks the master proce
ss variable while the slave is
in manual. This causes the setpoint of the master to vary indirectly in response
to manual output changes in the slave loop. When the system is switched to
auto, the master setpoint switches from track to local, and there is no process
upset because the track function eliminates any deviation in the master loop.
• Since the control element is directly manipulated by the sla
ve, the master is
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