Should the SIS interlock be activated in case of a loss of instrument signal?
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As shown in the figure, it is an interlock device signal based on temperature, pressure, and an emergency button; both of the input values set are HH. However, I have considered whether a signal disconnection or short circuit in the instrument, resulting in a loss of monitoring, would cause the interlock to activate If it isn’t implemented, does that mean there is no protection? If implemented, can such logic meet the requirements? Thank you~!
The fail-safe type must definitely operate when the signal is lost. But on the other hand, I wonder if the level of reliability at this point is sufficient; perhaps a majority-of-three voting system should be employed?
If the signal is lost, the SIS system must take action; if it happens to reach a very high value, wouldn’t that be dangerous?
If no action is taken, then what’s the point of making such settings? It is itself a logical circuit; regardless of whether the signal is true or false, interlocking is triggered once the conditions are met!
Yes, in my previous job I worked in power plants where there was a high level of signal redundancy; signal loss would cause the equipment to shut down. But this is a reactor, and I decided to use just these 2 variables, with HH as the trigger condition. I also suggested a \"three-out-of-two\" mechanism for the industrial control design, but since this is a reactor, there are no extra openings available, and making changes would incur high costs.
I don’t quite understand it either; it involves on-site maintenance of hardware instruments, and I’m also learning about the software aspect
What you say makes sense, but what I mean is which internal program triggers an action when a signal is lost – that’s the concept. In industrial control design, a loss of signal does not trigger interlocks
Yes, given the condition of protection, loss of monitoring should trigger it. What I don’t understand is through which signal input it gets triggered; isn’t it taken from HH? I don’t see it mentioned that it’s lost; I’m not very familiar with this software, so I hope you can help~ Thank you
If it’s for SIS, a proper hazop/LOPA analysis must be conducted first to determine how many points or just one point is needed to ensure achievement of the desired SIL level; the associated instruments also need to meet the required standards – it can’t be decided arbitrarily. However, power plants generally don’t have SIS, so this process doesn’t exist. But ESD and things like that are similar as well.
The input signal should be adjustable, that is, to determine what value appears on the channel when the signal is lost; otherwise, the way the program is written will need to be changed