How to read a linkage map
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How do I read this sequential logic diagram? ? ? ?
A very standard chain diagram. Valve shutdown condition: DCS HS switched to CLOSE, or HH is triggered. At this point, the on-site output remains at 0, and the valve stays closed. Valve opening condition: DCS HS set to OPEN, HH disappears, and the reset button is pressed simultaneously. At this point, the on-site output remains at 1, and the valve stays open.
This is logical operation; the notation A is used rarely – most of the time the & symbol or AND is employed. Chain diagrams should include symbolic annotations; once one understands RS flip-flops, one can understand how valves are switched on and off
The signal generated by the DCS is only sent out when the liquid level is below the set value; if there is a high-level alarm, then S will be locked and will not meet the output requirements. R is the reset button – pressing it allows operation once the liquid level drops. That’s how I understand it