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.

Measuring and Plotting Resonances with a Loop Probe

ESD tests