Patent ID: 8739636

Claim:
A electromagnetic flow meter comprising: a magnetic excitation coil disposed with a direction in which a magnetic field thereof is generated being perpendicular to a direction of flow of a fluid that flows through a measuring tube; a magnetic excitation circuit that provides a magnetic excitation electric current to the magnetic excitation coil alternatingly in a positive direction and in a negative direction, with non-magnetic-excitation periods interposed therebetween, and provides a positive magnetic excitation period and a negative magnetic excitation period either before and after, or after and before, each of the non-magnetic-excitation periods; a first electrode and a second electrode, disposed facing each other within the measuring tube across the direction of flow of the fluid flowing in the measuring tube and perpendicular to the direction of the magnetic field generated by the magnetic excitation coil; a flow rate measuring circuit that outputs, as a flow rate measurement signal, a signal in accordance with the flow rate of the fluid that flows in the measuring tube, based on a signal electromotive force that is produced between the first and second electrodes: a between-electrodes voltage sum calculator that calculates, as a sum of voltages between the electrodes, the sum of a voltage produced at the first electrode and a voltage produced at the second electrode, for each first and second period, when the non-magnetic-excitation period until a predetermined amount of time elapses from commencement of a transition from the positive magnetic excitation period to the non-magnetic-excitation period is defined as a first period and the non-magnetic-excitation period until a predetermined amount of time elapses from commencement of a transition from the negative magnetic excitation period to the non-magnetic-excitation period is defined as a second period; a fault evaluator that evaluates a fault in the electromagnetic flow meter based on the sum of the voltages between the electrodes for each first and second period, calculated by the between-electrodes voltage sum calculator; and a frequency component extractor that extracts only a specific frequency component from the sum of the voltages between electrodes, for each first and second period, calculated by the between-electrodes voltage sum calculator, wherein: the fault evaluator evaluates a fault in the electromagnetic flow meter based on the sum of the voltages between the electrodes for the specific frequency component, for each first and second period, extracted by the frequency component extractor.