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Thread: Grounding boxes?

  1. #101
    Join Date: Nov 2011

    Location: Seaton, Devon, UK

    Posts: 13,239
    I'm Adrian.

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    Quote Originally Posted by Mr. C View Post
    Lol oddly enough I do for at least 30 hours a week my lab is very well shielded.

    Here is a very odd but strangely true scenario, earlier this year I was working on a new pre amplifier design and was finishing off its ac line filtration circuit during pre compliance testing. The previous week I had just upgrade the labs mains power circuits and lighting to LED's so feeling pleased with my efforts I set up the equipment for the EC stands required Cisper 16. Now for this you need a isolation transformer for the DUT and the ground plane.

    After around 30m minutes of testing I was getting so real spurious readings really struggled to get my head around them. I ended up tearing down the set up and taking to measuring the individual instruments themselves just to try and eliminate the blasted common mode noise.

    Turn out to be a rather expensive bench power supply causing a heap of CMN, no here is the strange thing, even with the unit connected via an isolation (which lifts the earth) transformer the noise was still present. So even after switching the unit off at the power switch the noise is still present???

    Ok must be me going somewhat mad, so I took out the mains plug from the bench psu guess what STILL there

    Now the scopes and analysers are power by one side of the mains circuit, the other power supplies, iso transformers dc loads and ac power supplies are powered by the other side of the CU.

    Now one of the new LED lights is an overhead bench unit for intricate work it has a delightful SMPS though it is one the scope side of the mains, well taking this out of the socket removed all of the noise from the dc power supply even with the unit UNPLUGGED.

    This is an example of radiated RF in the real world and the switching frequncy 67Khz you really could not make this up, you do need ot be on your toes when taking low level measurements.

    A poxy SMPS caused almost a days worth of testing time loss, project completion time -1 day experience gained invaluable
    Interesting, is this not the basis of one of Tesla’s key power transmission experiments, but I might be confusing it with another phenomenon?


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  2. #102
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 1,861
    I'm Dennis.

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    I recently did some reading online on RF fields, my concern being with mobile phone relay masts, of which there are about ten on a block of flats 30 metres from my home.

    My concern is with the profusity of equipment generating RF, each adding to the hash, and more specifically the effects of constructive interference. (Addition of peaks in the waveforms). This will inevitably happen because there are so many different frequencies being transmitted,; there are people who line their bedrooms in metal sheeting.

  3. #103
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

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    I have similar experience in my new [relatively] workshop, with All LED lighting, the bloody things are so noisey, the one i have above my bench is paticularly problematic when testing high gain Audio circuits, i have to turn it off, which pretty much negates the whole reason of having a nice bright light over the area your working in! I usualy have to resort to using a conventional bulb set up in some cases.
    Quote Originally Posted by Mr. C View Post
    Lol oddly enough I do for at least 30 hours a week my lab is very well shielded.

    Here is a very odd but strangely true scenario, earlier this year I was working on a new pre amplifier design and was finishing off its ac line filtration circuit during pre compliance testing. The previous week I had just upgrade the labs mains power circuits and lighting to LED's so feeling pleased with my efforts I set up the equipment for the EC stands required Cisper 16. Now for this you need a isolation transformer for the DUT and the ground plane.

    After around 30m minutes of testing I was getting so real spurious readings really struggled to get my head around them. I ended up tearing down the set up and taking to measuring the individual instruments themselves just to try and eliminate the blasted common mode noise.

    Turn out to be a rather expensive bench power supply causing a heap of CMN, no here is the strange thing, even with the unit connected via an isolation (which lifts the earth) transformer the noise was still present. So even after switching the unit off at the power switch the noise is still present???

    Ok must be me going somewhat mad, so I took out the mains plug from the bench psu guess what STILL there

    Now the scopes and analysers are power by one side of the mains circuit, the other power supplies, iso transformers dc loads and ac power supplies are powered by the other side of the CU.

    Now one of the new LED lights is an overhead bench unit for intricate work it has a delightful SMPS though it is one the scope side of the mains, well taking this out of the socket removed all of the noise from the dc power supply even with the unit UNPLUGGED.

    This is an example of radiated RF in the real world and the switching frequncy 67Khz you really could not make this up, you do need ot be on your toes when taking low level measurements.

    A poxy SMPS caused almost a days worth of testing time loss, project completion time -1 day experience gained invaluable
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
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  4. #104
    Join Date: Jan 2008

    Location: Gerrards Cross

    Posts: 2,990
    I'm Tony.

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    Anthony

    Thinking back I have had a couple of occasions like this, hindsight a wonderful thing!
    Coherent Systems
    Real high end sound with musicality not hifi

  5. #105
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

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    Indeed!
    Quote Originally Posted by Mr. C View Post
    Anthony
    hindsight a wonderful thing!
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

    Matthew 5:10

  6. #106
    Join Date: Mar 2014

    Location: West Wales

    Posts: 843
    I'm malcolm.

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    Quote Originally Posted by Pharos View Post
    I recently did some reading online on RF fields, my concern being with mobile phone relay masts, of which there are about ten on a block of flats 30 metres from my home.

    My concern is with the profusity of equipment generating RF, each adding to the hash, and more specifically the effects of constructive interference. (Addition of peaks in the waveforms). This will inevitably happen because there are so many different frequencies being transmitted,; there are people who line their bedrooms in metal sheeting.
    Best thing to line with is pre-nuclear lead, cuts background radiation as well.
    Audiophile Tosher

  7. #107
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 1,861
    I'm Dennis.

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    Lead wallpaper rolls?

  8. #108
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

    Default

    Quote Originally Posted by Pharos View Post
    Lead wallpaper rolls?
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

    Matthew 5:10

  9. #109
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 99,005
    I'm Grant.

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    love survivalists..

    here is the "wrong rec room" scene from tremors

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  10. #110
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

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    Quote Originally Posted by Pharos View Post
    Lead wallpaper rolls?
    Not tried that yet. Got lead toilet paper though.
    It is impossible for anything digital to sound analogue, because it isn't analogue!

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