For prevention of effect of background noise, the alternator is enclosed in an acrylic box for simple noise insulation. The alternator is driven by a drive motor. The MI-1235 microphone and the MI-3111 microphone preamplifier pick up the alternator's noise and output a signal. The CF-4700 FFT comparator receives the signal and performs FFT frequency analysis. A defective product generates amplitude-modulated noise (whining noise). The amplitude-modulated noise (whining noise) appears on the power spectrum as adjacent multiple frequency peaks. OK/NG judgment of the alternator is made depending on the peak level on the power spectrum of whining noise.

The block comparator function makes OK/NG judgment by the block area (maximum setup: 20 blocks) set in a certain frequency range and level range. Six kinds of judgment methods (level, peak level, peak max, insideMax, partial overall or area rate of content) are available for each block. Also the digital I/O function enables control via PLC using comparator output.

The measurement results can be stored into a PC via LAN or RS-232C interface.