Cables for niche applications

Nothing is easy in machine vision, not even cables. Take Clean Rooms for example. I didn’t know this, but apparently when cables rub together the resulting particles can be a big headache. Makes sense I suppose.

So if you’re putting a vision system in to that kind of environment you should talk to someone about the cables. Ron Folkeringa of Intercon 1would suggest you talk to him. And to help you out, he wrote “Connectors and Cables Revisited”, published on the Quality Magazine website January 3^rd, 2014.

It’s a useful article, especially for anyone dealing with hazardous environments, or the aforementioned Clean Rooms. But you might also want to check out my comment on cables from two years back, “Cables, the Rodney Dangerfield of machine vision?”

Going the distance

Picking a camera is hard work. There’s resolution and lens format, sensor type and frame rate, and then there’s the interface standard, in terms of both speed and range. Now if you’re able to put the PC close to the camera pretty much any interface – GigE, FireWire, USB, or CameraLink - will span the distance, but there are many applications where the two are, of necessity, separated.

As a rough guide, if you have more than 3m between them you should give some thought to the most appropriate standard. Sometimes though this limits your choice of camera, but never fear, Andy Wilson is here.

No, Andy’s not going to stretch your cables, but he does have some advice on how to make them reach further. “Clearing Up Choices for Cabling and Connectors,” (Vision Systems Design, September 1^st, 2012, points out that most of the standard interfaces now have some kind of extender technology. If this is something you might need to deal with, I suggest you click the link above and save Andy’s article in your Favorites.

Cables, the Rodney Dangerfield of machine vision?

Cables – those plastic-coated wires that enable your vision system to do something useful – can’t get no respect. They’re bent, twisted and folded to fit in the tightest of spaces, and the connectors …. They get shoved in and pulled out like a … well I had a crude analogy in mind but I shan’t print it here. You know what I mean.

If you want your vision system to be robust and industrial, (and who doesn’t?) then you need to look after your cables, AND use industrial connectors. Thumbscrews are good, but what I really like are the M12-type connectors I’ve seen on the latest cameras from Matrox and NI.

And according to “Connectors and Cables 101” (another Vision & Sensors article, January 4^th, 2012,) I am not alone in this. Click the link to learn what Intercon 1 has to say on the subject.

Cables for GigE machine vision

I’ve only recently made the move into GigE vision (I’m not really a “leading edge” kind of guy,) and I wasn’t aware that I needed to think about what type of Ethernet cables I needed. Call me simple-minded if you want, but I though all cables with a RJ45 end connector were the same.

Oh how naive of me.

Turns out that it’s actually quite important to buy CAT6 rather than CAT5 cabling. Apparently even CAT5e, (the highest grade of CAT5,) isn’t as good as CAT6. The main differences seem to be that CAT6 allows more data to be transmitted over longer distances with greater reliability, thanks to it having more than double the frequency range and less significantly attenuation.
If you’re interested in learning more, here are a couple of links:

http://www.lanshack.com/cat5e-tutorial.aspx
http://www.broadbandutopia.com/caandcaco.html

On a separate note, can I just mention that I will be taking a few days off over the Holidays but hope to get a coupple of posts in before New Year.

Best wishes to you all.

Another source for machine vision cables

Cables are the unsung heroes of machine vision: if it weren’t for their sterling efforts all that camera work in converting photons to bits would be for naught. Yet so often the cable is an afterthought. And when we do come to hook camera to PC, how often do we find that the cable on hand wont reach, or the connector doesn’t fit? Add to that the need for screw-in connectors and suddenly you’re scratching your head wondering where to go for parts.

Wonder no more, because today I would like to share with you a new cable vendor. Well they’re new to me but I believe they’ve been in business for some time. I’m talking about Newnex Technology Corp.

California-based Newnex offer an extraordinarily wide range of Firewire, USB and GigE cables, and if you still can’t find what you need they’ll even make up a custom cable for you.

Something to add to your “Favorites” if nothing else.

Shielding: Sexy? No. Important? Yes

The signals that travel from camera to PC are pretty darned important, so you’d do well to ensure they don’t get contaminated by electrical noise. For a concise introduction to the arcane subject of shielding electrical cables, read “An Update on Shielding” by Jon Titus, published in Design News November 1st, 2009.

To reinforce the message, let me share with you a note posted on the Cognex/DVT SmartList discussion board. A questioner had asked if he could make up his own cable, to which the extremely knowledgeable Ken Scofield of Cognex replied, “Cognex sells only cables that we have extensively tested for resistance to various forms of interference. We do run into very significant problems with customers using home-made cables. Long cable runs or improperly constructed cables can easily pick up induced signals that are strong enough to be mistaken as real signals, or which degrade true signals enough to drop communications.”

In other words, don’t be tempted to cut corners on cabling.

Cables – your weakest link?

When you think about it, the cables that you use to connect your machine vision camera to your PC are pretty darned important. You rely on them to transport your data bits quickly and without error, and to do so for many years without complaint.

That’s why I recommend you read “Clean Connections” by Andy Wilson, published in the September Vision Systems Design. It’s not the sexiest topic, to be sure, but Andy does a great job of explaining what can go wrong, how cables are tested, and why you should care.

I’m not going to repeat what he has to say, but I would like to add a few cable hints of my own:

1. Keep the camera still. If your system is designed so that the camera has to be moved you’ve added a potential failure mode, so try very hard to avoid camera motion.
2. Use screw connectors. Even if nothing moves in your system, there will be some vibration that could cause push fit connectors to work loose.
3. Keep cable runs as short as possible.
4. Watch out for sources of electromagnetic interference. Welding is perhaps the most obvious but there can be others.

Minimizing electrical noise

Factories are electrically noisy places, (acoustically too, I know,) and from time to time this can cause problems with sensitive electronics, as found in machine vision systems. One tip, building on my previous post, “Who needs long cables?” is to keep cable runs to the absolute minimum, and definitely avoid coiling up cables that are too long.

There’s a lot more information in a fascinating (no, seriously,) paper I found on the Basler web site, with the snappy title of “Avoiding EMI and ESD Problems in Basler Camera Link, IEEE1394, and GigE Camera Installations.”

You can probably just skim the text, but the diagrams are genuinely interesting. Apparently, and this was news to me, the big issue is ground loops, which create electrical noise and are best avoided by having a single point ground.

So next time you’re struggling with strange or seemingly random events, remember to consider electrical noise.

Who needs long cables?

I’ve tended to scratch my head when the subject of maximum cable lengths comes up. In my world, which is industrial manufacturing, I can pretty much always put a PC close to the camera. As a result, I’ve never paid much attention to the sales people whose chief claim is that I can put the camera a hundred meters away from the PC. I just tend to wonder why I would ever want to do that.

But from the latest Basler newsletter comes an interesting story of a machine vision/security application. This concerns the inspection of shipping containers at harbor gates, and clearly it’s an application where cable length matters. You should read the article for full details, but suffice to say that this seems to be a great application for GigE camera technology.