Abstract: Apparatus for monitoring the functioning of motor driven equipment, including current sensing apparatus connectable to the power input of the motor and producing a current signal; signal correction apparatus receiving as input the current signal and operative to demodulate the current signal, filter the current signal to retain low frequencies thereof, and convert the current signal from analog to digital form and producing a corrected signal; a memory; a controller in operative connection with the memory, receiving the corrected signal, and having a calibration state and an operation state, and operative, when in the calibration state, to compute the calibration norm of the corrected signal based partly on data contained in the memory and to store the calibration norm in the memory and operative, when in the operation state, to compute the operation norm of the corrected signal based partly on data contained in the memory and to compare the operation norm with the stored calibration norm and to produce a fun