Control loop limit
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1. What is the effect of the soft limit of the main circuit 20908A on the secondary circuit 20901A in terms of the cascade control between the furnace outlet temperature 20908A and the furnace inlet flow rate 20901A? 2. Does it serve to set a control limit for the flow rate in the secondary circuit, or to limit the valve position in that circuit (since the secondary circuit has a soft limit control)?
1. Temperature control constitutes the main circuit; its output value serves as the setpoint for the FIC. The limits of this main circuit prevent large fluctuations in the setpoint for flow control. There are four parallel feed streams, which help to ensure uniform feeding； 2. The secondary circuit has a low output limit to prevent the flow rate of a single stream from being too low. 3. The above stability is only maintained under stable conditions; when there are significant external fluctuations, the four feed streams may compete with each other for flow rate.