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EMC Engineering: Signal Return and Shield Conduction Tests

Using external clip lead


Above: Clip lead attached to an oscilloscope or spectrum analyzer.

  • Helps determine proper signal-return (or shield) connection back to enclosure.
  • Connect one-meter-long clip lead to various shield connection points on all I/O cable ports.
  • Clamp a current probe around the cable (or measure the amount emissions radiated).
  • If no current is measured or clip lead has no effect on radiated emissions, that shield connection point is connected back to enclosure shielding okay.

Measuring plated shield

  • Using a “four-point” probe permits one to verify sheet resistance and , therefore, the thickness of vapor-deposited (or plated) metallic shields
  • A 4-terminal (for resistance) DMM (digital multimeter) is needed.
  • Knowing the thickness, one can calculate the shielding effectiveness, given the manufacturer’s equation.

       

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Updated: Wednesday, 2007-10-03 1:44 PST