Installation of remote IO boxes in explosion-proof areas
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Hello, experts. The customer’s control room is located far away from the workshop (over 100 meters), and there are a large number of valve devices. If a cable were to be run from each device to the control room, the cost would be extremely high. The customer is now asking whether it is possible to install the IO module in the explosion-proof control box on site. Each flameproof box is connected to the control room via fiber optic cables, which significantly reduces cable installation work. The site is in a Zone 2 explosion-proof environment. But some people say this method works, while others say it doesn’t. Has anyone had similar experiences or approaches? Moreover, the regulations do not state that IO modules cannot be installed inside explosion-proof boxes.
Sure, that’s exactly what Emerson did at Wanhua. There’s a page from his family’s PPT introduction that you can take a look at.
Yes, the fiber optic communication used at Baosteel’s Zhanjiang plant works
That’s great; I really need these things right now
If it has to be done when there is no other option, then maintenance becomes an issue, as it is not allowed to open the control cabinet on site
It can be placed on-site, but there are distance requirements; I remember it must be more than 30 meters away from the device location. Follow the **provisions; otherwise, the cost of making corrections later will be higher
It’s very picky about the environment; after all, the conditions on-site are certainly not as good as those in a control room. It’s also unknown what the failure rate will be in the long term, but maintenance efforts will definitely be substantial
Indeed, maintenance is a problem; the cover cannot be opened while it’s powered on. 100 meters is considered a relatively short distance; it’s best to be able to reach the control room. Alternatively, use intrinsically safe accessories and conduct a comprehensive certification for the entire cabinet (at least at the increased safety level Exe); this way, certain preventive measures can be in place during maintenance, allowing the cabinet doors to still be opened.
Wanhua’s 1 million tons per year ethylene plant adopted this approach, primarily to save money. However, this solution was opposed by all the instrument engineers working on the ethylene plant, whose main concern was related to maintenance issues. In the end, it was the management who decided to go with this approach. Although all the equipment on site are positive-pressure explosion-proof cabinets, in the event of a failure later on, there might be an awkward situation where no one is available to sign the relevant form. When formulating a plan, consideration should not be given only to costs, but also to subsequent issues such as ease of maintenance. Relatively speaking, I think Honeywell’s solution might be a bit better. His technology is similar to Emerson’s, except that he places the positive pressure explosion-proof control cabinet outside the unit, which saves costs and facilitates maintenance. The above is for the original poster’s reference.