5/05 failures? Bad Run? Radios?

Hello,
We've had 2 SLC 5/05's fail within the last 6 months. I posted here as I was trying to troubleshoot them, tried what was suggested, but in the end, I replaced the 5/05's and the problems went away. They were intermittently going to hard fault, program would be completely gone, and going online to re-download was increasingly hit or miss.

I was told that someone here, specifically Ken Roach I think, might be able to tell me if the serial numbers from the hardware can be linked to a potentially known “bad run” in production from A.B. I've included a pic of each of the failed 5/05 nameplate stickers.

Another theory that was brought to my attention involves the use of Radios (walky-talky’s) all around our facility. All the engineers and techs who operate or view HMI’s located at PLC panels are required to where Motorola xts 1500 radios. Our plc’s are located in non-metallic nema 3R enclosures. If an operator was using an HMI and talking on the radio, the radio may be as close as maybe 2ft or so from the 5/05 processor (through the enclosure). A friend told me he once was told that there could be issues, and not believing it, he put a radio right up to a SLC and it in fact “died”. Has anyone had this problem? And if it is an issue, how could I prevent it? “Un-training” the operators would be difficult to say the least. What about some metal shielding on the inside of the panel door?

Thanks for any input,
Byron

I've seen PLC-2s fault when a radio was keyed nearby and I've also seen thermocouple transmitters go berserk in the presence of walkie-talkies.

I don't doubt that you could fault any PLC processor if the signal is strong enough.

Is it possible hand-held radios are the problem? Sure. Is it probable? I'm not so sure.

A few questions. Is this a new installation? Was there a problem before six months ago? are the radios a new factor?

The Motorola radios you mention are pretty good size, up to 5 watts. So, it's possible it could scramble the memory of the PLC, but then you say that re-downloading the program wasn't working properly. While I could see a 5-watt radio scrambling the memory, I'm having a harder time believing it would do permanent damage to the PLC.

I worked at one site that had drives that were sensitive to radios. A 2-watt radio within 5 feet with the cabinet doors open would cause the controller to rail and send the motors into full-speed. Not a good condition. We solved that by building a Faraday cage around the drive and put ferrite beads on the wiring. Because the manual override controls were located inside the cabinet and we couldn't just keep the doors closed. But even with this we never actually broke anything, turn off the radio everything work just fine.

The surest way is to try some experiments and see what happens when you key up your radio right next to the PLC. Of course this isn't likely to a popular idea. If you have lab where you can do this away from production it might be worth a shot.

Also check out the power supply, is it affected by RF? A power supply with a funky output could actually damage components.

Next would be replace the enclosure with a properly grounded metal enclosure. Also, make sure all the cables going into the box are shielded or in conduit.

It could just be you've had a run bad luck and none of this will do any good.

bawaller,

i've heard of train radios killing plc's.

do you have a line filter on the plc power side?

i do know that brown outs, power surges, voltage drops will kill the plc memory - learned that the hard way.

regards,
james

Not sure about the 5/05 processors specifically, but I do know that 2-way radios can cause some weird and surprising problems.

I work in the entertainment industry, and I've seen more than one case of a walkie-talkie causing a theatrical lighting console to reboot when it was keyed to transmit. It forced a VERY unplanned reboot which surprised the heck out of the light board operator mid show, and surprised the actors and audience with an unplanned blackout. However, the effects from RF that I've seen are transient, and never appeared to cause any permanent damage.

I know that's more anecdotal than directly helpful; does any other equipment (HMI, VFD, etc...) seem to be affected by your radios?


-rpoet

I know that's more anecdotal than directly helpful; does any other equipment (HMI, VFD, etc...) seem to be affected by your radios?

Click to expand...

I had a coworker with a pacemaker that had problems around radios/walkie-talkie.

Mickey said:

I had a coworker with a pacemaker that had problems around radios/walkie-talkie.

Click to expand...

That's actually pretty terrifying. Aren't those things supposed to be tested against RF interference?


rpoet

bawaller said:

Hello,
We've had 2 SLC 5/05's fail within the last 6 months. I posted
...
Has anyone had this problem? And if it is an issue, how could I prevent it? “Un-training” the operators would be difficult to say the least. What about some metal shielding on the inside of the panel door?

Thanks for any input,
Byron

Click to expand...

Actually, the Siemens G120 AC drive has a distance prohibitation of 2 meters, for hand-held radios.

So, it is not unheard of.

rpoet said:

That's actually pretty terrifying. Aren't those things supposed to be tested against RF interference?


rpoet

Click to expand...

This was 30 years ago, I hope they are built a little better now.

I don't have any inside information about any possible SLC-5/05 manufacturing problems; I don't work at RA Tech Support anymore and use almost entirely ControlLogix family controllers now. In general, the SLC-5/05 is a sturdy and reliable controller.

Do the enclosures have a good steel backplane with solid grounds ? Check out the RA motion control guide to grounding and bonding... sometimes you need to use braided ground straps and/or cages when there's strong interference and no metal enclosure.

My favorite radio warning is when I found myself in the Chelan County jail's booking area and saw a GE 90-70 controller in a cabinet with prominent "NO MOTOROLA 2-WAY USE WITHIN 50 FEET" stickers on it.