Can the pumps interlocked by the SIS system be controlled in the DCS?
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If the feed pump in the tank area is interlocked with the liquid level in the SIS system for emergency shutdown, can it be operated via the DCS when there is no such interlock? How can this be achieved?
Sure, send a shutdown signal from the SIS system to the DCS
It is generally not started from the DCS; instead, it should be stopped from the DCS, by sending a DO signal to SIS, which then stops the pump. However, this reduces the security of the system.
Yes, you can set on/off buttons in DCS; if necessary, automatic start can also be configured. However, the SIS interlock pump-shutdown signal should be sent to the DCS and incorporated into the startup circuit, so that when the interlock triggers a shutdown, the DCS cannot start the pump. The rest can be implemented by the electrical engineering team.
Can the electrical engineering team achieve this by connecting two contactors in series within the motor control cabinet?
Yes, in the electrical control circuit, the DCS startup node and the SIS interlock shutdown node can be connected in series within the same circuit. But this is less secure and convenient than imposing restrictions between control systems, as one DCS engineer can control the processes on all system sides. To be honest, most electrical systems use relay control, and their reliability is still somewhat inferior compared to that of integrated systems.
It’s not that I’m against anything; it’s just since the Tianjin incident. The locals are filled with fear; they treat foreign standards such as IEC61508 and IEC61511 as precious treasures without even trying to understand them or incorporate them. Just force it to fit. Think about it: during the Type 3 gauge era, when there was no control system, problems arose. DCS is also unreliable; a whole new system is needed. Following this logic, I think it’s safer to have one system per circuit. That’s how humans are; they’re afraid of this and worried about that, never at ease with anything.
I’m not a professional; should the signal be sent to the advanced SIS first, with another route going to the DCS, or what should be done? What’s the difference?
The interlock stop signals are fed directly into the SIS, while the normal start/stop signals go to the DCS; the activation and deactivation of interlocks are handled by the SIS.
It’s complicated to have a pump that receives signals from two different systems; it’s better to carry out the operations within the SIS system as well, since this won’t add many extra points.
Is it feasible to add a separate valve in front of the feed pump, controlled separately by the SIS? ? ? ?