[T9 man]

Will try to make this brief and hopefully straight forward. The hum is caused by the deterioration of the margin voltage caused by variations in the DC power supply which does have a slight AC ripple in the line voltage through the bridge rectifier and smoothing capacitors, which produces an electromagnetic interference (EMI), to the corresponding power induced in a conducting wire antenna (CWA). DC voltages in the electrode circuit in magnetic-conductive flow measurement with periodically reversed DC magnetic field in which the useful signal is obtained by sampling and storing the signal voltage after each reversal of the magnetic field at opposite polarity values of the magnetic field during a sampling time interval and forming the difference of the stored sampled values, and wherein in a compensating time interval following each sampling time interval a compensation voltage is produced by sampling and storing the signal voltage, which compensation voltage is superimposed oppositely on the signal voltage for compensating the signal voltage within the compensation time interval to the value zero and is retained until the next compensation time interval, wherein each compensation time interval lies within the time interval corresponding to the switched-on magnetic field.