Two tanks are connected in parallel, and each tank has high/low level interlocks; feeding is controlled via a single DCS. What’s wrong with this setup?
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As shown in the diagram, the two tanks are connected in parallel; both tanks have high level/high low level interlocks, which via a DCS interlock control the feeding to the automatic dosing unit. What is wrong with this setup? Why don’t design institutes recommend doing this?
As a supplementary note, these two slots are not connected
Has one DCS not fulfilled the role of one in operation and one as a backup?
Under normal circumstances, when both liquid levels are at the HH level, the activation of both signals will cause the motor to stop; in such a case, there should be two interlock circuits. If it is a chain system, a change in the HH value of one of the liquid levels will cause a change in the digital signal of the chain (from 1 to 0), which will result in the motor stopping. If at that time the other liquid level is not full, it will be necessary to restart the motor manually, and in such a case the chain design would be unreasonable. If there are two chains, the motor will stop only when both levels are high (i.e., when there is a change in both digital signals); this design is more reasonable.
I roughly understand what it means: AB represents an \"AND\" logic, rather than an \"OR\" logic; the system can be shut down only when all the shutdown conditions are met.