4-20 ma Current Loops – Answering a Few Questions

Wow, there must be a lot of people interested in current loops;  that’s the most comments I’ve received in a short period of time after the post.  I’m going to take a few minutes here to address a few questions.  Meanwhile, I’m just about finished with the “how to assemble the panel post” and hope to have that up some time tomorrow if not sooner.

Big D.  wondered if the panel was U.L. listed and the answer to that is that the assembled panel is not listed, but all of the components used in the assembly, with the exception of the data logger are (more on the data logger in a minute).  That’s one of the advantages you get by using the commercial and process grade components vs. Radio Shack components.  I would have to be a listed panel fabrication shop to actually put a U.L. label on the panel.

That being said, I can tell you that to the best of my knowledge, we have not had any problems deploying the loggers and the power panels in any of the jurisdictions we work in.  I’m up and down the West Coast a lot and into the Rockies, but as a company, we work all over the United States.  In the few instances where this topic came up, the fact that the parts were U.L. listed, were enclosed in a U.L. listed enclosure, and were for temporary monitoring rather than a permanent installation were the keys to not having a problem with the authorities.  Having the assembly be neatly assembled probably didn’t hurt either.

I think things might be different if we intended to permanently install the panel in some locations.  I that case, I think the panel would need to be assembled by a fabricator who could label the assembly in addition to having listed components.  The two products would be virtually identical with the exception of the label on the assembly.  So, what I am saying here is that everything in the post would be applicable, it would just need to be assembled by someone with the proper certifications if you wanted to install it permanently.  I suspect if you dig around in some of your control panels that are legacy systems using current loops, you would find an arrangement similar to what we are discussing in this string of posts.

TECNOS asked about wireless data acquisition, which is a rapidly emerging technology. I personally have not had much direct experience with it as of yet, but I know of folks like Mike Brambley at Pacific Northwest National Laboratory (PNNL) who have been doing research and development work for several years now.  Mike publishes a lot including a fairly recent paper titled Are Wireless Sensors and Controls Ready for the Building Automation Industry? Selected Case Studies and Technology Development Activities, so you may want to take a look at that and some of the other stuff he has published.

Incidentally, inserting the links reminds me that we are still working out some of the bugs with the move to the new blogging platform, one of them being that when I embed a link, it doesn’t seem to work.  I suspect that the bug is me, and am planning a conference call with the development guys tomorrow or the next day so they can set me straight.   Until then, if you mouse over the link, you can read it, even if you can click on it and have it work (at least that’s the case on my system).

I also see that several comments have come in from previous posts, some of which appear to be spam of some kind, but a few of which are questions I will try to answer in a post later this week.   Meanwhile, thanks for your support and taking the time to read the blog.  I hope everyone is having an enjoyable spring weekend.

David Sellers
Senior Engineer – Facility Dynamics Engineering

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