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  1. #11
    Quote Originally Posted by Lee Roberts View Post
    Bit early for Turkey isn't it, we've not even got Halloween out the way yet?
    .....I heard "All I Want For Christmas" by Mariah Carey ont' radio a few days back.....

  2. #12
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 17 Hours Ago Has been a member for 1-2 years. Has a total post count of 142. Received thanks 22 times, giving thanks to others 3 times.
    Quote Originally Posted by Voicecoil View Post
    I'm pretty sure there wouldn't be any problems with commoning up the 3 earth conductors to a single pin at the spindle, it's all about balancing inter-conductor capacitance along the length of the cable, a few cm at the far end is unlikely to upset things. And the outer screen would be best connected only at the VFD end to avoid HF earth currents, so likely you could do it with a standard 4 pin plug - if you could fit the rather fat cable into said plug of course.
    I have to say I'm unconvinced that's worth the expense. Coming from a communications background, to avoid significant radiation of noise I'd want each winding fed with it's own balanced, twisted pair. Telephones have been doing it this way since Alexander Graham Bell was in charge, twisted pairs minimise both radiation and reception of noise, and Ethernet cables are done the same way. I don't know if these VD cables are constructed as three twisted pairs but for minimal noise radiation they would need to be.

    While we're on about it, using a twisted pair rather than loose wires for connecting limit switches etc. to your BOB might help reject noise pickup even for non-balanced inputs.

    Kit
    Last edited by Kitwn; 1 Week Ago at 01:17 AM.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  3. #13
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 17 Hours Ago Has been a member for 1-2 years. Has a total post count of 142. Received thanks 22 times, giving thanks to others 3 times.
    Quote Originally Posted by Voicecoil View Post
    .....I heard "All I Want For Christmas" by Mariah Carey ont' radio a few days back.....
    Here in Oz some people ( mostly poms and other northern hemisphere ex-pats I suspect) celebrate 'Christmas in July' because that's when it's cold here and is the best time of year for enjoying huge roast dinners, mulled wine and other such traditional fare.

    Kit

    PS How come there's no smiley wearing a Santa hat? What's Lee playing at?
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  4. #14
    Quote Originally Posted by Kitwn View Post
    . I don't know if these VD cables are constructed as three twisted pairs but for minimal noise radiation they would need to be.
    From what I read it's more of 2 interleaved twisted triplets - a bit like 1.5x the starquad cable the BBC OB guys I worked with were so fond of in high noise situations. You might be right in that at 3x twisted pair would work better as far as EMI goes, it would all depend on the switching points of the VFD. However it would make the cable even more bulky and/or increase copper losses, so that's probably why it's not been done. It would be nice to investigate this further, but as no-one makes a 1mm2 such cable and it probably won't matter much on a 2.5m run, I have more important things to concentrate on.
    While we're on about it, using a twisted pair rather than loose wires for connecting limit switches etc. to your BOB might help reject noise pickup even for non-balanced inputs.
    Kit
    I've already done this. The leads on the proximity sensors were woefully short, so had to be extended anyway, so I chopped them back to a sensible minimum length and extended with my favourite Mogami screened twisted pair cable. Why they don't make such sensors with a screened cable to start with I don't understand.
    Last edited by Voicecoil; 1 Week Ago at 05:26 AM.

  5. #15
    Quote Originally Posted by Kitwn View Post
    PS How come there's no smiley wearing a Santa hat? What's Lee playing at?
    Good point!

  6. #16
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 17 Hours Ago Has been a member for 1-2 years. Has a total post count of 142. Received thanks 22 times, giving thanks to others 3 times.
    Quote Originally Posted by Voicecoil View Post
    ........a bit like 1.5x the starquad cable the BBC OB guys I worked with were so fond of in high noise situations
    Ha! Owning up to an Auntie connection now! I haven't heard about star quad since my earliest days as a trainee back at Wood Norton back when Noel Edmonds was a lad.
    I'm sure the cable manufacturers are brainy enough to construct their products in a suitably 3-phase field-cancelling way.

    Kit
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  7. #17
    Quote Originally Posted by Kitwn View Post
    Ha! Owning up to an Auntie connection now!
    Kit
    Back in the day I worked for a company supplying audio equipment to the Beeb, mostly for OB trucks, got to know one or two of their engineers quite well during the acceptance testing. I got to see some of the syllabus from the training courses at Wood Norton, very good stuff: when it got watered down/shut down/hived off it was a great loss to the industry IMHO.

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