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cabling mystery

Discussion in 'Electronic Basics' started by Fritz Oppliger, May 3, 2005.

  1. To protect an analog signal we replaced plain ribbon cable with shielded
    ribbon cable.
    The shielding we connected to earth ground on ONE end. Now the humidity
    reading is erratic. Switching back to plain unshielded ribbon and the
    problem goes away. This defies all the rules in my book - What could I
    be overlooking?
     
  2. John - KD5YI

    John - KD5YI Guest

    Earth ground? Try connecting the shield to the circuit ground (common) at
    one end. Then try the other end.

    Good luck.

    John
     
  3. Art

    Art Guest

    Actually you may be inducing a ground loop signal by connecting one end to a
    known 'earth ground'. This will tend to skew the information [create noise]
    at the receiving end. As posted, try connecting one end to equipment
    reference [ground] rather than the true 'earth ground'. Seen a lot of
    problems in CCTV systems as a result of earthing the cable shields.
     
  4. The aim was to reduce the chance of getting zapped by "tribo-electrics"
    inside this dry box with fans and sundry metal mesh trays. Which are
    grounded to earth ground, more or less, through steel pins resting on
    aluminum rails... I did not want lightning to strike signal ground, nor
    any wire in that harness. My fear of these discharges may be overblown but
    I'm chasing gremlins & have no clue what to measure where!
    This is my introduction to ground loops then. Although I have difficulty
    seeing a "loop" in this scenario.
    To thicken the plot, how about connecting shield to ANALOG ground? I'd
    hate to have the ADC zapped!

    Thank you for your insights.


     
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