What is the difference between closing permitted by the process and tripping due to process interlocks?
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The signal sent by the instrument to the electrical system – what is the difference between closing allowed by the process and closing due to process interlocks?
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Of the two you mentioned, the former are startup conditions, while the latter are interlock conditions. The condition permitting startup is a status check to be performed before the machine starts; if the conditions are not met, startup is not possible. The interlock condition is that once the machine has started up, it will be interlocked and stopped if the conditions for triggering are met. The difference is that one is before startup, and the other is after startup.
As a supplementary point, allowing the switch to close generally does not affect the operation of the unit even if it is disconnected after the motor starts. Logically, after the switch is closed, the contactor that drives the motor ensures that the power supply circuit for the motor remains locked in place; the node that permits the switch to close is located within this locking circuit, whereas the node for process interlock shutdown is located outside of it. After the motor starts and self-locking is established, the closing signal can be disconnected, allowing the motor to operate normally ； The process interlock trip signal is disconnected, and the motor stops operating.
After closing, the contactor that drives the motor causes the motor’s power supply circuit to self-lock; the node that permits the closing signal is located within the self-locking circuit, whereas the process interlock shutdown node is located outside of this self-locking circuit. After the motor starts and self-locking is established, the closing signal can be disconnected, allowing the motor to operate normally ； The process interlock trip signal is disconnected, and the motor stops operating.
I understand the working principle, but I don’t know how to set the conditions for the process! In some processes, it is difficult to distinguish between allowing the circuit to be closed and using interlocking to cause it to open; it is thought that in any case, if the conditions are not met, closing the circuit will have the same effect