[With Images] Solving PID Interlock Examples
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1. A rectangle enclosed by a diamond, containing the letter I and a circuit number – this must be the interlock function of SIS. For example, in I-0117 shown in the diagram, 4 signals are fed in and 1 signal causes the pump to stop; the specific logical judgments are likely shown in the logic interlock diagram. 2. A single diamond shape containing the letter I without a loop number – is this DCS interlocking? Is there any logical judgment in this? Without a circuit number, how can I find the logic interlock diagram?
Take a look at the logical or control scheme; it should be clearly stated there. I guess the pump stops and the shut-off valves HV0111 HV0112 are closed due to low flow rate or low liquid level in R101, or perhaps an emergency stop button is present on site that directly stops the pump and closes those shut-off valves, or there are soft buttons on the DCS system that do the same. Feel free to point out any mistakes!
In the P&ID diagram, the interlock section only shows the signal transmission relationships; it does not reveal the interlock logic. The logic of the interlock section should be presented in the ‘Interlock System Logic Diagram’.
Right! I just guessed based on common reasoning; you’re absolutely right! It should be understood according to the logical expression given in the logic diagram!
I-0117 should have a dedicated logical description or logic diagram, which includes three I’s; HS0121 involves the buttons on-site as well as the soft control buttons on the DCS for performing corresponding operations