This is a pulsing motor drive unit that keeps a tight tolerance on speed by varying the duration of the drive pulses as it monitors a speed sensing tachometer feedback signal. This type of set-up is notorious for the amount of generated RF signal that shows up as AC leakage current in amounts that can top out over 2,000 uAmps (2 milliamps). Hettich has always claimed that their machines were built to EN 61010 standards, and were considered “Laboratory Equipment”, not medical devices. As such, Hettich’s older products were not designed to mitigate the amount of leakage current their devices generate. In 2005, Hettich realized that deeper U.S. market penetration would require them to address the issue, especially to appeal to the hospital market and their very strict fire codes.
Today, Hettich’s newer designs are manufactured with better electronics that keep the AC leakage current below 500 uAmps. In addition, most models include a redundant chassis grounding post. This device must be attached through a medical-grade connector to an earth ground that is separate from the centrifuge’s power source (a cold water pipe, for example). With this properly installed grounding, the centrifuge will pass a single-fault condition of the AC leakage current check with close to 0 uAmp measurement.