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<p>The levels of Electromagnetic Interference (EMI) generated by two standard models of Uninterruptible Power Supplies (UPS) were examined. Conducted current measurements were made on all conductors exiting and entering two standard UPS units between the frequency range of 60-Hz up to 50 MHz. EMI reduction actions were undertaken on both units, and the reduction in EMI current resulting from these actions was determined. The before and after mitigation results were compared with EMI limits suggested by available specifications, standards, and other related documents.   The results show that a significant reduction in the level of EMI can be achieved in low-to-modest size UPSs using inexpensive, standard, and commercially available filters, provided the filters are installed in an effective manner. The reduction of EMI to harmless levels at radio-receiving and data-processing sites is shown to be feasible.
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<br>Subjects: Electromagnetic interference; Electric power supplies to apparatus; Computers; Power supply</div>
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Beran, Edward W.</div>
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