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Have you ever seen a ratio controller? One that controls, lets say, the flow into, two different vessels, in this case two reactors. We set the ratio flow on two different control loops controlling two different control valves. This way you can choose to increase or decrease flow to the reactors as long as the total percentage equals 100.
The problem is that the feed to these two valves come from another vessel that has it's own level control valve. What happens in an upset situation is that if the ratio controllers have satisfied their ratio at one flow rate and the flow rate through the level control valve swings, you get out of control and wind out your level control loop and never catch up, because the ratio control is still at the same ratio, i.e.,same output. You end up having to put the ratio controllers on manual and sling them open until the level can find set point.
I thought about running the level with the ratio loops and just put the level loop in manual at 100%, but I am not sure how to do the ratio logic if I do so.
Anyone have any suggestions...
The problem is that the feed to these two valves come from another vessel that has it's own level control valve. What happens in an upset situation is that if the ratio controllers have satisfied their ratio at one flow rate and the flow rate through the level control valve swings, you get out of control and wind out your level control loop and never catch up, because the ratio control is still at the same ratio, i.e.,same output. You end up having to put the ratio controllers on manual and sling them open until the level can find set point.
I thought about running the level with the ratio loops and just put the level loop in manual at 100%, but I am not sure how to do the ratio logic if I do so.
Anyone have any suggestions...