Common control loops

This chapter will describe some common loops encountered in process control. The loop characteristics, type of controller to use, response, tuning, and limitations will all be examined. 

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All of these systems have some common control loops. The system pressure is controlled by manipulating the fresh feed of A (F0A). The concentration controller with ratio control is used to control reactor inlet gas composition by manipulating the fresh feed of B (F0B). Bypassing (Fhy) around the FEHE is used to control gas mixture temperature Tmix. Reactor inlet temperature (Tin or T ) is controlled by manipulating the furnace heat input QF. The setpoints of these two temperature controllers are the same, and the controller output signals are split-ranged so that bypassing and furnace heat input cannot occur simultaneously. 

Flow control is probably the most common control loop in most processes. Typically, a liquid or gas flow rate is maintained in a pipe by a throttling valve downstream of the measurement, as shown in Figure 3.4(A). Locating the valve upstream of the measurement is not recommended because many measurement problems can arise. 

Common Control Loop Control with Adaptive Sensing... 

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