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Further Results using Hall Sensors

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  • davidj95650
    See message 1207, Results from a new A-Theory . An e-mailer inquired if flux-coupling to the main core might influence the results I reported about the
    Message 1 of 1 , Nov 9, 2003
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      See message 1207, "Results from a new A-Theory".
      An e-mailer inquired if flux-coupling to the main core
      might influence the results I reported about the magnetic
      field from the output coil being greater on the outside of
      the core leg than in the interior of the core space.
      Based on the measured inductance change with the ferrite
      sense coils in air and then in place at the core leg,
      there is some coupling (about a 40% change in inductance ),
      but this is not enough to skew the results I measured. To
      further eliminate any flux coupling, I built a fourth
      set-up using a Honeywell AMCC-100 core. This is a small
      core, and the size difference provides further variation.
      Instead of ferrite sense coils, I used Allegro/Sprague
      UGN-3503U Hall-Effect sensors. These devices have a
      linear response to about 23 kHz and a sensitivity of
      about 1.3 mV output per gauss. Prior to installing them
      near the core leg, I measured their sensitivity and chose
      two devices whose output was within five per-cent when
      exposed to the same field from a solenoid coil resonating
      at 10 kHz. I used balsa wood to provide a spacer and
      support so that the devices were about one-tenth inch
      away from the core surface, about one-tenth inch from the
      first layer of the output coil, and held in the center of
      the core leg. These supports were made as closely
      similar as was practical. Unfortunately, I neglected to
      add an electrostatic shield, so the measurements are
      sensitive to frequency. Therefore, I made four
      measurements at four separate frequencies to determine a
      trend of frequency response. The results at the lowest
      frequency I tried, 1.23 kHz, were output-side sensor:
      49 mV, interior sensor: 11 mV for a ratio of 4.5 to 1.
      At the highest frequency I made measurements, 3.71 kHz,
      the output-side sensor: 78 mV, the interior sensor: 38 mV,
      for a ratio of 2.1 to 1. These devices are packaged in
      plastic and have an internal operational-amplifier which
      is clearly sensitive to external electric fields. A more
      precise set-up should use a thin brass layer to provide an
      electrostatic shield between the output coil and the
      sensors.

      David J.
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