New ac micro-ammeter for leakage current measurement of biomedical equipment

A new inexpensive current probe for on‐line leakage current measurement of biomedical devices in hospital environment is described. The prototype is designed to detect and measure leakage currents on the ground wire of the device’s power cord so that its integrity can be monitored in real time. Realized with a sensing coil specially matched to a low‐noise op amp, this probe adds only negligible impedance on the monitored ground lines. From this preliminary study about the device’s metrological performances, a sensitivity of 10 nArms for a current range 1–500 μArms has emerged, together with a mean linearity error of 0.03% and a frequency response flat within 1% of gain from 50 to 2000 Hz.