Interlock logic
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1 Can this diagram implement the logic of starting the pump when the liquid level is high and stopping it when the liquid level is low? 2 How can the output status on the right side be related to the motor schematic? In the motor schematic, stopping the pump is represented by a normally closed contact, while starting the pump is represented by a normally open contact. On this diagram, low liquid level corresponds to output 1; how can the contact be in a closed state when the output is 1? It should be turned on, right? The motor can stop only when the contacts are open. The requirement for Process 3 is that two pumps operate one after the other as a backup system; there is a manual selection for which pump to use. Does this need to be shown in the logic diagram? 4 Is the interlock bypass on the right a soft switch configured by the DCS? Because this switch cannot be seen in the schematic diagram
3. The process requirements are not met; this logic applies to both pumps simultaneously, with no design options available.
1 It’s logically possible, but it should be able to be optimized further. 2. As can be seen from the diagram, there should be one DO point per pump. If your actual circuit uses two contacts for start/stop control, you need to use an output relay to make the conversion; the normal open or normal closed configuration can be achieved depending on the wiring of the relay. 3 If it is one in use and one as a backup, this needs to be indicated, just like in the case of a \"chain bypass\" – there must be a switch for switching between them. 4 Which one does the interlock bypass on the right refer to? I didn’t notice.
Thank you for your reply. Regarding the second point: in the actual circuit, two contacts are used to control start and stop – the contact that stops the pump is a normally closed contact, while the contact that starts the pump is a normally open contact. Do you mean the output relay for conversion as referring to the output relay of the PLC system? When the liquid level is low, the output is 1; I want to stop the pump, which means that the normally closed contact should be opened. In that case, the PLC’s output relay should be energized, and this corresponds exactly to the output of 1 when the liquid level is low. Is that correct? Regarding the third point: if a changeover switch is to be added, how should it be installed? As for the fourth point, I made a mistake; it should be the interlock bypass on the left. Is this bypass switch a software switch configured within the DCS system?
Thank you for your reply. Regarding the second point: in the actual circuit, two contacts are used to control start and stop – the contact that stops the pump is a normally closed contact, while the contact that starts the pump is a normally open contact. Do you mean the output relay for conversion as referring to the output relay of the PLC system? When the liquid level is low, the output is 1; I want to stop the pump, which means that the normally closed contact should be opened. In that case, the PLC’s output relay should be energized, and this corresponds exactly to the output of 1 when the liquid level is low. Is that correct? Regarding the third point: if a changeover switch is to be added, how should it be installed? As for the fourth point, I made a mistake; it should be the interlock bypass on the left. Is this bypass switch a software switch configured within the DCS system?
Relays have normally open and normally closed contacts; you can tell just by looking at them. The relay can be located on the PLC side or on the power cabinet side; the principle remains the same. Just add a switch like before, so that only the circuit to which it is switched will be active. I’m not quite sure what that ‘A’ means:P