Figure 8-20: PID Function Block Diagram for Feedforward Control
A. Outlet temperature input
B. AI function block
C. PID function block
D. AO function block
E. Out
F. Inlet temperature input
Cascade control with master and slave loops
Situation
A slave loop is added to a basic proportional/integral derivative (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.
Figure 8-21 illustrates the process instrumentation diagram.
Manual FOUNDATION
™
Fieldbus
00809-0500-4880 December 2022
Rosemount OCX8800A 187
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