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equinoxavinc
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Join Date: Mar 2007
Posts: 4

Electronics, Field Service

05/21/2011 7:45 PM

Hi All,

I've got a problem with a receiver that receives PLC Digital info that is filtered off the power line. The 62khz information is being overwhelmed by a 62.5khz noise that is sporadic, intermittent and rises slowly and drops off slowly over a three to six hour period. The noise floor becomes 60% of the the total signal. My nest trip to the location I will have a spectrum analyzer, hoping the noise is there, and try to isolate the source hoping the noise is internal to the location.

I have been a long time follower of this forum and respect the advice the pro's have. Any input to this situation would be deeply appreciated.

Sincerely,

overwhelmed by noise
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Iris
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Join Date: Jul 2010
Posts: 669
Good Answers: 176
#1

Re: Electronics, Field Service

05/22/2011 9:36 AM

Well, Google brings up ballast operation in that frequency band. Sound close enough for your situation?

Electronic ballasts use power supply circuits that vary widely in frequency. Although they are not intentional radiators, lighting fixtures emit fields that can interact with other devices operating at the same frequency. The typical frequency of electronic ballasts may vary from 20 kHz to 100 kHz. This frequency range is a public domain and band widths are not licensed or managed by the FCC.

GE UltraMax ballasts operate between 56 kHz to 62 kHz depending on the lamp and ballast factor used. GE UltraMax H ballasts typically operate in the 61.5 - 62 kHz range and N & L ballasts operate in the 56 - 58 kHz range. The interaction between GE UltraMax ballast and Sensormatic EAS systems is dependent on several factors: fixture size, bulbs, wiring in the fixture, ballast fundamental operating frequency and ballast harmonic distortion (the inadvertent emission of multiples of the fundamental frequency).

http://www.gelighting.com/na/business_lighting/education_resources/literature_library/white_papers/download/121879_understanding_interferance.pdf
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engineertony
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Join Date: May 2011
Posts: 102
Good Answers: 2
#2
In reply to #1

Re: Electronics, Field Service

05/23/2011 6:49 AM

Just checked Philips and they give a string of compliance standards and a frequency >42kHz. Tridonic give 40 to 100 kHz. So we would expect a big lighting installation to be radiating a range of frequencies.

If this is 62.5 kHz it might be traceable to one specific source, then changing the ballast could solve your problem.

The other direction may be to look at what's happening with the PLC. Is it simply an on/off logic signal which has been set at 62 kHz? It must have been tuned at both ends at some time, perhaps a word with the suppliers about shifting the mains borne frequency would solve it.
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Rorschach
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#3

Re: Electronics, Field Service

05/23/2011 9:35 AM

If the problem is indeed lighting, then perhaps cycling breakers for various lighting circuits might help you pin down the offending circuit. go around the location and make sure everything is on. if the noise occurs, then you good chance it is on-location, and start turning things off at the circuit breaker panel until the noise goes away. that will isolate the offending circuit. Perhaps installing an EMI filter on that branch then will solve your problem.

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equinoxavinc
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Join Date: Mar 2007
Posts: 4
#4

Re: Electronics, Field Service

05/23/2011 10:30 AM

The lighting is on 24/7 and the receiver works on frequencies from 40 thru 62khz.Only the 62KHZ frequency is being drowned out by a precis 62.5 KHZ frequency. My next trip there I an bringing a spectrum analyzer and scoping the room were the receiver is located to see if the problem is internal or external.
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WoodwardDL
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Location: Anthem, AZ
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#5

Re: Electronics, Field Service

05/23/2011 11:02 AM

The noise could also be the sampling frequency for a Switched Mode Power Supply. For a test, unplug all such devices and run your receiver for a day.
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equinoxavinc
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Join Date: Mar 2007
Posts: 4
#7
In reply to #5

Re: Electronics, Field Service

05/23/2011 11:46 AM

I forgot,three switching mode modem power supplies are on the list for remove and replacement.
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engineertony
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#6

Re: Electronics, Field Service

05/23/2011 11:04 AM

Precise 62.5 kHz can only be one single source.
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StandardsGuy
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#8

Re: Electronics, Field Service

05/24/2011 7:48 PM

Computers which have switching power supplies could be your problem.

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equinoxavinc
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Join Date: Mar 2007
Posts: 4
#9
In reply to #8

Re: Electronics, Field Service

05/26/2011 11:26 AM

I visited the site yesterday and this is the analyzer image of one of the channels of noise that is representative of the entire location.

We have hundreds of units in the field and this is the only one with this problem. All switching mode P. S. were removed and replaced, all grounds and neutral return checked for problems. This noise floor comes and goes and runs for a period of two or three hours the 26 hours. My next trip is to sweep the entire area with an antenna and spectrum analyzer to try and pin out the strongest radiation of this 62KHZ noise, any suggestions?
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Users who posted comments:

engineertony (2); equinoxavinc (3); Iris (1); Rorschach (1); StandardsGuy (1); WoodwardDL (1)

Previous in Forum: Tarantula Conductor   Next in Forum: Electromagnetic Field Collapse Principals
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