Cascade Control With Master And Slave Loops - Emerson Rosemount OCX 8800 Reference Manual

Figure 7-20:
7.9.11

Cascade control with master and slave loops

Situation
A slave loop is added to a basic PID control configuration to measure and control steam
flow to the steam heater. Variations in the steam pressure cause the temperature in the
heat exchanger to change. The temperature variation will later be sensed by TT101. The
temperature controller modifies the valve position to compensate for the steam pressure
change. The process is slow and causes variations in the product temperature.
illustrates the process instrumentation diagram.
Reference Manual
PID function block diagram for feedforward control
Foundation Fieldbus
Figure 7-21
167