PURPOSE: To get a power source frequency by detecting a power source induction noise (AC noise) frequency, perform excitation and sampling synchronized therewith and easily eliminate AC noise.
CONSTITUTION: A coil is excited by an excitation circuit 11, electromotive force detected by an electrode is sampled, A/D conversion 2 is performed, spectral analysis 3 of its sampled data is conducted and each frequency component (spectrum) of a flow signal is obtained. After a power source frequency is obtained from its spectrum by a power source frequency getting circuit 5 and its frequency power source waveform and sampled data are superposed on each other, a synchronizing position is found out by means of the spectral analysis and an AC synchronization signal is produced by a power source synchronization signal (AC synchronization signal) production circuit 10. The excitation circuit 11, a sampling circuit 1 are controlled and excitation and sampling synchronized with the power source frequency are performed.
SETA NOBUAKI
SAITO KOJI
HITACHI INSTRUMENTS ENG