Sensor for in Situ Validation of Cable Transfer Functions

The transfer impedance of cables is an important design parameter to evaluate EM immunity of systems, and many laboratory test set-ups have been described to determine and verify the transfer impedance of cables and connectors. In complex systems with high performance demands in situ validation is preferred. For this purpose we developed a measurement procedure, which determines the transfer function of a cable (including connectors and attached electronics) with respect to the common mode current over the cable and the currents over the inner wires of a multi-conductor cable. A common mode current is injected via an EM injection clamp and measured with a standard current probe. For measuring the differential mode currents a special sensor was designed in a way that it can be inserted in the cable under test at existing interconnections. Its impact on both the common and differential mode circuits is kept to a minimum. In addition, it does not significantly increase the transfer function of the complete system. The sensor and measurement procedure have been successfully applied in the validation process of a magnetic resonance system.