Electro-optical sensor for shielding-effectiveness measurements of motor-control-unit enclosures

This paper presents shielding effectiveness measurements of a small enclosure for motor control units in two frequency ranges from 10 kHz to 200 MHz and 200 MHz up to 3 GHz. Measurements take place in two different measurement environments, namely in a TEM-cell and in front of an absorber-covered wall. Due to little space in partly equipped enclosures, small field probes have to be used. This paper shows measurements done with a small electro-optical E-field sensor, which is used in various configurations according to the dynamic range. The measurements are done with the enclosures fully equipped with their electronic devices. Thus, the results presented here give a good overview of most realistic, possible EMC-threats of such control-units, which can hardly be obtained from simulations. The main aim of this paper is to compare the modifications of the sensor system and the two frequency ranges. Finally it is shown, that common shielded enclosures provide sufficient shielding effectiveness in the relevant frequency ranges.