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[Neilsen]

hello, i am currently working on design a waste heat boiler and i need to accomplish the control of this boiler. But there is an instrument called "summing relay" in my control system, can somebody tell me what it is about and its usage? and can someone give opinion about my control system? thanks in advance!!

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[Padmakar Katre]

Dear,
From your drawing it seems that you are asking about the three element control in which you have a linear signal from Level Transmitter and Non-linear signal from the two flow transmitters (steam and boiler feed water), inthis case you always need to linearize the the signal from the Flow Transmitters by sqaure rooting the electronic signal representating the differential pressure across the flow element so the function of the summing relay is to linearize flow signal and add the linear level signal and send it to the controller as PV feed back. Hope you will understand. Please do ask if the doubt persists.