In this process, raw maple syrup is heated by steam to evaporate water and make it more concentrated. An analytical sugar-concentration analyzer at the end monitors the concentration of the finished syrup:
A flowmeter has been installed on the raw syrup line to monitor changes in feed flow rate. Operations personnel have determined that variations in feed flow rate are adversely affecting product quality, and have asked you to implement a solution to stabilize product quality (syrup concentration) despite changes in flow rate.
Modify the control strategy shown in the diagram to achieve better sugar-concentration control despite significant changes in raw syrup feed flow.
Feedforward action from the feed flow transmitter to the steam valve is one solution to this problem:
Question For You:
Perhaps the single most common mistake we make when planning a feedforward system is mis-placing the location of the summing function block, where the load signal adds to the feedback control signal.
Explain why the load signal should always be added to the feedback controller output signal, and never to the feedback controller PV signal.
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