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Thread: See if you can figure this one out.....

  1. #16
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    Default Re: See if you can figure this one out.....

    Linden--Drives generate odd multiple harmonics and their corresponding magnetic fields. That is, 1x 60 Hz, 3x 60 Hz, 5X 60 Hz etc. Any frequency that is an even multiple of 60 Hz will not be produced by the drive. I simply provided an example at 240 Hz which is 4x 60 Hz. The drive harmonic amplitudes will typically diminish as frequency increases. However, PWM drives can produce interference at fairly high frequencies. Again, this problem is probably best approached with very narrow band filtering set to an even multiple of 60 Hz. By the way, the exception to all of this is if you have DC motors. The DC drives will produce fields at 360 Hz and a few multiples beyond that. It is unlikely that the chiller and related equipment use DC motors. Waste water plants, particularly older plants, could have DC drives for some of their equipment. These days, AC drives will be more likely in most industries.

  2. #17
    Junior Member Linden Riddle's Avatar
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    Default Re: See if you can figure this one out.....

    No problem understanding your original post. The information makes sense but in a limited way. Tell me how 240 hz would be beneficial for locating lines situated underneath the electric duct?

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    Senior Member beyond help's Avatar
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    Default Re: See if you can figure this one out.....

    It's an alien. Oh crap!!!!!
    STRESS: The confusion created when one's mind overrides the body's basic desire to choke the living daylights out of some idiot who desperately deserves it.

  4. #19
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    Default Re: See if you can figure this one out.....

    Linden: If your utility is beneath electrical conductors associated with a VFD and you used a tracer frequency of 240 Hz, then you would be unlikely to be interfered with by the electrical conductors. This assumes your receiver has very narrow band filters.

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    Default Re: See if you can figure this one out.....

    I knew I read something on here about this ran into this yesterday. Ifindit what finally worked? The only machine I have acess to is rd8000. We can pick up something elsw if needed. I am pretty sure the problem was vfd as this was a huge bank of chillers.

  6. #21
    Senior Member ProfessionalLocator's Avatar
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    Default Re: See if you can figure this one out.....

    If you are near a strong magnetic field it can and will induce currents / voltage inside your transmitters and receivers. The components inside the equipment act like the core of a transformer and output a induced current and the frequency of the output varies depending on the internal circuit. Our equipment is all battery powered, a DC steady current with no frequency, and mostly we are exposing it to a strong 60 cycle field and all kinds of internal harmonics will result. Our equipment may have filters but I expect this is to filter out a weak external source, not an internally generated unwanted frequency. The very circuit made to filter out unwanted frequencies will have it's own unwanted frequencies induced by the strong external magnetic field.

    None of our equipment I have seen taken apart is shielded against a strong external magnetic field.

    You might try warping the equipment with aluminum foil but covering the antenna will not allow the receiver to work. While you are at it wrap your head with aluminum foil. People will not be coming out to ask you what you are doing.

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    Default Re: See if you can figure this one out.....

    Pro I felt like I was wrapped in tin foil the way the people that hired us were looking at us. I'm sure they thought we were incompetent. We tried everything the 2 of us could come up with.

  8. #23
    Conservative Meanie ifinditunderground's Avatar
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    Default Re: See if you can figure this one out.....

    The Metrotech I5000 completely negated any effects of the Variable Frequency Drives found at each location.
    There is a fine line between "Hobby" and "Mental Illness."
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