| 摘要 |
PROBLEM TO BE SOLVED: To provide an electromagnetic flowmeter surely performing vacant detection. SOLUTION: Positive and negative pulse current generated in a constant current source 21 is applied between electrodes 2a, 2b through a switch 25. An alternating current voltage signal in response to impedance between both the electrodes generated by the application of the pulse current is converted in the impedance with preamplifiers 5a, 5b to be differentially amplified with a differential amplifier 6. The output signal of the differential amplifier 6 is amplified with an alternating current amplifier 22, after it is rectified with a rectifying circuit 23 to be converted into direct current voltage, converted with a V/F converter 24, converted into a frequency signal proportional to direct current voltage, and taken in CPU 11 through an I/O interface 10. CPU 11 compares it with a reference frequency signal stored to RAM 13, and a vacant detection output signal is generated in the comparison result.
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