Cable Shielding Effectiveness Measurement

When a cable specification calls for 90 db of rf shielding the 100 db dynamic range allows a 10 db margin in the measurement range.

Cable shielding effectiveness measurement.

For these products we primarily use two techniques the triaxial fixture method and the mode stirred method. The test method permits measurement of long specimens using high currents with a uniform current distribution along the cable shield. There could also be changes in compliance standards. This is a typical margin recommended by various industry specifications.

Measurement method for determining shielding effectiveness of cable feedthroughs. The shielding effectiveness is measured by comparing the reading of reference and the load devices. This method is effective for frequencies less than 500 megahertz. To verify the periodic calibration two gold standards are employed.

Our most common request is to measure se for connectors and cables. Making accurate measurements is a challenge because shields have many different shapes and purposes. For example housings connectors or cables all use shields and each application requires a unique test fixture to ensure accurate and repeatable se measurements. A shielding unit is inserted through the box s opening.

Ventilation is another example and one that is usually problematic with regards to shielding effectiveness. Cable interconnects which allow cables inside the cage to connect to cables outside may undergo modification for additional connectors that damage the shielding integrity. A plot of the chamber s dynamic range is shown in figure 2. The method is offered as a standard technique for measuring the shielding effectiveness of shielded cables.

Measurements were made in the frequency range 0 5 to 100 mhz.