Wireless microphone interference

  • Thread starter Timothy L. Tartamella
  • Start date
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Thread Starter

Timothy L. Tartamella

Has anyone ever heard of a wireless microphone causing noise interference on a controller interface? How can such interference be prevented?
 
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Bob Gillooly

Yes Timothy,
I have heard of it, and have experienced it on drive systems. RF and EMI can raise havic with unprotected and sensitive systems. Your case is RF radio Frequency noise. Guarding against this is difficult but doable. My recommendation would be to read Don White's articles. He is the president of emf-emi control Inc. in Montross Va 22065. The articles are like a book, and the topic studies like a course. but you know your application and can quickly pull out the specific info. you need. I will fax to you what ever I can. The first line of this article reads as follows. "A plant Tech in a nuclear plant uses a walkie-talkie and vital controls in the plant malfunction. (send your fax #)
 
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Michael Griffin

I have seen two-way radios affecting electronically controlled devices (e.g. servo valves). We tried various types of shielding and
grounding without success. Eventually, we realised that we were wasting our time. Even if we were able to shield the equipment, how could we be sure that we were completely successful? We had the radios for at least a year before we noticed any problem.

Our conclusion was that in our application, there were two different problems we had to solve. One problem was safety. That had to be solved by proper guarding and system interlocking with reliable hardware. Any electronic device which may function in an unsafe manner if it is affected by a radio should be rendered safe by some other means (e.g. a brake or
blocking valve) when someone is exposed to it.

The other problem was process quality and reliability. That was addressed by proper instruction and training of the personnel to not use their radios close to an operating machine.

However, I'm still not sure where this leaves devices such as light curtains. These are safety devices but they contain electronics. If there is any possibility of these being affected by a radio, the only realistic solution is to ban radio transmitters from the plant. This may include cell phones. You would need to talk to the representatives of the safety device companies about the degree of radio interference they can tolerate.


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Michael Griffin
London, Ont. Canada
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W
Sure. Happens all the time. Shield the controller, or change the operating frequency of the wireless mike.

Just stand next to some (usually pre-1994) controllers and key a handytalkie sometime and watch the indicator. After the EC EMI Directive and the CE mark testing,lots of this went away.

Walt Boyes, putting his tinfoil hat on :))
 
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Bob Peterson

5TI and PM550 PLCs were infamous for their reaction to walkie-talkies that might be keyed up in their vicinity. TI solved this problem by introducing shielded cables for connecting up the I/O racks to the CPUs.

As I recall, it was only a problem if the WT was keyed up inside the control panels (this was back in the days of walk-in control panels, mind you).

My suspision is that a good metal housing and proper shielding and grounding, coupled with some common sense (like instructing operators not to use WTs while inside a control panel), will alleviate most of these problems. You might want to do some testing to be sure.

This is one of several reasons I remain somewhat hostile to the use of plastic bodied, field mounted electronic devices . I see no way to
effectively shield them, although I have been assured by several manufacturers of such equipment that this is not a problem.

Bob Peterson
 
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Johan Bengtsson

Handling RF is tricky but not undoable if you think about it when you start doing the electronics. (proper ground planes is a very
good start, it does (of course) not solve everything but almost) Good manufacturers take care of this at the construction stage and
handles a lot of RF and other similar disturbances.

Here in europe there is now a requirement to mark things with a CE mark and that is supposed (among other things) to mean the device can handle some certain amount of RF and that it does not emit more than a certain amount by itself. For radio transmitters it is about not emitting RF on frequencies it is not supposed to and not more
power than it is supposed to and so on.

A quick test (of course not covering everything but anyway...) is to put a mobile phone (GSM works at least) close to the thing (you have
to dial someone first). If it works fine, well first test passed, if not throw out that piece of equipment if it can be any treat to someone or to the product quality. Have you noticed that some amplifiers picks up a pulsing noice when you have a GSM phone within approx a meter and are talking to someone (and at some other times too) but not when it is close to other. The amplifier in my computer speakers both here at work and at home
picks it up very loud, but my home stereo don't. This is the difference between a bad design and a good one.

The noice can of course be picked up thru cables too, a proper shield, twisted cables and a proper grounding reduces most of it.



/Johan Bengtsson

Do you need education in the area of automation?
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P&L, Innovation in training
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]
Internet: http://www.pol.se/
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W
There are coatings that can be applied to the interior of these plastic housings, but they are dubiously effective, IMHO. The best thing to do,
frankly, is to insist that what you buy meets the
EMC directive and carries the CE Mark. This has required many manufacturers to pay much closer attention to the on-board shielding and component choices they use in the design process.

I recall being in an underground pump station vault, in the mid 1980's, across the river from New York City, listening to Don Imus on the signal-out taps on a doppler flow meter... times _have_ changed.

Walt Boyes

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21118 SE 278th Place - Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142 ICQ: 59435534

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business consulting for the small and medium-sized
enterprise: http://www.waltboyes.com"
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Michael Griffin

At 15:25 08/11/01 -0500, Johan Bengtsson wrote:
<clip>
>Here in europe there is now a requirement to mark things with a CE
>mark and that is supposed (among other things) to mean the device
>can handle some certain amount of RF and that it does not emit more
>than a certain amount by itself. For radio transmitters it is about
>not emitting RF on frequencies it is not supposed to and not more
>power than it is supposed to and so on.

Interestingly enough, the devices we were having problems with were from France, and are CE marked. However, the radios are not. If you want to rely on CE marking to avoid hardware with radio interference problems, then both the affected device and the transmitter need to be CE marked.
The older style two-way radios tend to emit more power and at a lower frequency than the new models (or cellphones) do.

>A quick test (of course not covering everything but anyway...) is to
>put a mobile phone (GSM works at least) close to the thing (you have
>to dial someone first). If it works fine, well first test passed, if
>not throw out that piece of equipment if it can be any treat to
>someone or to the product quality.
<clip>

We should keep in mind that there are two different issues involved. One is safety, in which case field testing is not an acceptable solution for obvious reasons. The other situation is quality and productivity, where you may take certain risks if you feel they are justified.

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Michael Griffin
London, Ont. Canada
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