Spring Sizzle and Placebos
Dear Reader:
Spring!
Two forlorn sticks with little resemblance to arms are all that remain from my final snowman of the season. The kid’s sleds are stowed away. Cold rains have washed the salt from the roads, clearing the way to bring Dad’s toys out of the garage. Kids are playing in the streets, enjoying the extra hour of Daylight Savings Time (even if my headlights are back on for my drive into work each morning). As far as I’m concerned spring is officially here in Northern Illinois. Never mind last weekend’s snow – the power of positive thinking, with an assist from Climate Change®, will overcome.
But as the threat of heavy snows and cold rains fades, the prospect of equipment sizzling thunderstorms rises – it’s no coincidence that I had so many calls this week asking what I recommend for surge suppression on a gaggle of RS-485 applications.
- John called from Minnesota with gnawing concerns that their traffic information signs communication may prove to be susceptible to storm damage.
- Bill called about access control systems installed all over the world.
- Barbara called about the network of motion controllers she’s planning for a solar farm.
- Alex called about communications to generator-sets in remote Alaskan towns.
Each and every one of them asked what I recommend for surge suppression to protect their network.
Bzzzzzzzt.
Now – understand that B&B happens to build some of the worlds gnarliest data line surge protectors right here in our Ottawa, Illinois factory. I designed and tested many of them myself (even if it was in another decade...and not the last one).
You should buy one. You won’t need it to protect your network. You need it because your pointy haired boss, or your customer - the one with your office, home and cell phone numbers, expects you to say “yes, of course I’ve got a surge suppressor in there” – and you can puff your chest and point to this badass surge protector inside your cabinet. Go ahead and attach some wires to it for show.
Never under estimate the value of a good placebo.
Here is the secret – this is why your serial network is going to be rock-solid reliable.
It’s because, thanks to your experience, your diligence in studying the B&B web site, or listening to my sage advice – you are going to isolate each and every node of your serial network.
There’s a dirty little secret of serial communications, true for each of RS-232, RS-422 and RS-485. Unlike other wired connectivity standards (the plain old telephone system and Ethernet for example), there are no requirements for isolation. (By the way, USB shares this same flaw, so if you’re using it for anything more menacing than your speakers and printer, here is your fix).
You’ll find plenty of details on why isolation is superior to surge suppression (and many other gems) in the B&B Technical Library, but I’ll sum it up for you here.
Surge suppression attempts to divert excess energy to earth ground and away from your precious equipment. So if it suddenly sees a 400 volt spike between its data line and its earth ground line, it will shunt the resulting current off through its ground connection. Therein lies the rub (and this is only rub #1). Surges tend to be the result of a high frequency event with fast rise times. That means that the impedance of your ground connection needs to be tiny – fractions of an ohm and capable of carrying hundreds of amps for a split second. Easy to do at DC. Highly impractical at 10’s of MHz. It also means that without that earth ground wire properly installed, a surge suppressor’s about as useful as a solar powered flashlight.
That’s rub one. Rub two, the lesser known Shakespearian rub-a-dub, is that a surge suppressor requires its ground connection to be zero volts. If you’re under the misconception that earth ground is zero volts, banish the thought from your noggin and you’ll be on the path to communications reliability nirvana. Think of earth ground like the ocean’s elevation. The average elevation of the ocean is “sea level.” But pick an instant in time and at any one point the ocean's elevation is likely to be many meters above or below sea level. The voltage of your local earth ground behaves precisely the same way.
There you have it – now you know the secret to rock solid reliable communications. But how do you pull it off?
B&B is here to help. Here are your building blocks.
In many cases you need to make a conversion from RS-232 to RS-422 or RS-485. To do so, simply select an isolated converter. Shazam - you’ve isolated that particular node.
But what if you don’t need to make a conversion? Then you simply need an isolated repeater. Install an isolated repeater in front of your existing 232, 422 or 485 device to give it the isolation you wish it was born with.
We’ve got a family of inline isolated repeaters.
Or, bring out the big guns and use an industrial grade DIN rail or panel mount isolated repeater.
Are you intensely serious about your application’s reliability? Then check out this new family of uber-verters designed for the rigors of electrical substations, use them anytime that nothing but the best will do.
http://www.bb-europe.com/product_family.asp?FamilyId=642
And what about that placebo? Frankly, it’s easier to go ahead and stick one in your system than trying to explain all of this. And don’t forget to hang some wires off of it.
http://www.bb-europe.com/Subcategory.asp?SubCategoryId=94
Finally, don’t forget that each and every one of these products was designed with care and built with love right here in Illinois. This isn’t just about sunshine and lollipops. It means that when you need a converter we’ve got it and you can have it tomorrow. And if you need advice or support you know who to call. And if you happen to be in Europe, we keep another large supply of product in our Ireland office, giving you the same service and support. There’s nothing wrong with sunshine, lollipops and rainbows, but at the end of the day it's service and support that counts!
Happy Springtime Connections,
Mike Fahrion
e-support@bb-europe.com
+353 91 792444
P.S. Let me pre-empt several dozen likely emails extolling the virtues of surge suppression. It does have a place. Once every last node of your network is isolated, consider adding a surge suppressor to the location in your network with the best access to a central grounding system.
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