How to draw an interlock logic diagram?
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The pH control tank activates or deactivates the alkali addition pump based on the pH value; when pH ≥ 8.5, the alkali addition pump stops operating； If PH ≤ 6.5, start the alkali addition pump. If there is a reset button, does that mean that when drawing the interlock logic diagram, it’s sufficient to show only the high-interlock pump shutdown? Do I need to draw both high interlock and low interlock? For example, if the pump stops due to a high interlock, then pressing the reset button should either stop the pump from stopping again or start it up, right? So, what exactly should be done? I’m a bit confused now; if anyone knows, please give me some guidance. Thank you!
This post was last edited by jlshnlhj on 2022-2-20 21:26. Both high interlock/low interlock controls need to be drawn; otherwise it is incomplete. (If you are the designer, you need to make it clear to the constructors) ； It is a DCS configuration, designed to be clear for operators and easy for future personnel to understand). There are various methods to implement the high interlock/low interlock control scheme; a reset button should use an RS flip-flop approach.
Yes, I basically use RS flip-flops to draw interlock diagrams these days. If both high and low interlocks are shown, is the reset button the same?
It depends on the specific logic: is the reset button connected to the reset terminal of the RS flip-flop, or is it used to reset the logical program? Are you doing design or DCS configuration? If it is a configuration, the design drawing shall prevail.
All of them need to be done. Comparison — Output plus SR
This post was last edited by jlshnlhj on 2022-2-28 at 19:45. The design department in our company used to be part of the factory’s design team; it became an independent unit after the restructuring. The design drawings they provided were either principle block diagrams or logic diagrams (as shown below). They paid no attention to things such as automatic/manual switches, reset functions, switches for starting/maintaining the primary components, or interlock mechanisms for operation/shutdown – these had to be handled through DCS configuration. I wonder if you have such good luck. The logic is simple: reset does not refer to initialization after the machine stops; the DO output is 1, which activates the pump (the pump generally does not start with a value of 0, otherwise the circuit will be disconnected...). In addition, manual setting/reset is available (RS for setting/resetting), as manual control is required in certain special situations.