Is the pump shutdown signal designed to be “fail-safe”?
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In the DCS system, a pump stop signal is required; this signal is isolated through an intermediate relay and then provides a contact signal to the electrical MCC. The question is whether this relay should be designed to be energized when the pump is operating normally. If it is energized, a failure of the relay can lead to abnormal shutdown of the pump; if it is designed to be de-energized under normal conditions, such an issue will not occur. Do any experts working on the production front line have experience in this area?
Relays should be designed to remain energized under normal conditions, mainly for safety reasons.
The number of points is probably not high; there’s no need to use ESD even if the level of safety is high. It’s better to use a relay-based interlocking system. If you’re worried, you can use solid-state relays, but it seems like an overreaction. As for contact-type relays, their lifespan depends on the number of times they are switched; the likelihood of coil failures is low, as long as the contacts are in good condition
Whether it is designed to be \"fault-safe\" probably depends on your process. However, petrochemical facilities are generally designed with \"fault safety,\" meaning that the relays remain energized under normal conditions, which helps to detect power supply failures. If the relay is not powered, then in the event of an interlock requirement, a power failure could prevent the relay from operating, which would be serious. That’s why in petrochemical applications, it is common to design them to remain powered at all times, ensuring \"fault safety\"”
To add a few more points, the general design principle is to \"prefer malfunctioning rather than failing to operate when it’s necessary\", and this is done to ensure safety