Experimental Validation of Correction Factors for In Situ H-Field Measurements below 2 MHz

Abstract

A large number of devices cannot be tested in standard electromagnetic compatibility laboratories due to size, power or safety-related constraints. In these cases, the only viable alternative is the in situ approach. The reference standard for in situ testing, CISPR 11, proposes to evaluate the equipment's emissions in the 150 kHz to 30 MHz range through the measurement of the magnetic field at a 30 m distance. However, at such conditions, the said emissions are barely discernible from ambient noise and sometimes ensuring such fixed measuring distances is not even possible due to limitations of the test site. Emerging standards projects, e.g., CISPR 37, are considering setting the reference distance to 10 m while allowing measures at distances from 3 m to 30 m through the application of specific conversion factors to achieve a result that is comparable to the applicable disturbance limits. In this work, the corresponding magnetic field conversion factors are experimentally studied and validated from the in situ standpoint. Results obtained show an excellent match with the proposal in the latest CISPR 37 draft in the frequency range from 150 kHz to 2 MHz.