| 摘要 |
PROBLEM TO BE SOLVED: To attenuate the wandering of the measurement output of an electromagnetic flowmeter caused by the frequency noise of commercial power supply by providing a band attenuation filter' which attenuates a specific frequency component contained in sampled DC flow rate signals. SOLUTION: A band attenuation filter 4 attenuates the component (f) expressed by an expression f=|mfex±nfn|(where, fex, fn, and m and n respectively represent an exciting frequency, the frequency of commercial power supply, and positive integers) of the frequency components contained in a DC flow rate signal 13 sampled by means of a sample and hold section 3. Therefore, the wandering of the difference frequency component between the exciting frequency and the frequency of commercial power supply of the frequency components contained in the sampled DC flow rate signal 13, namely, the wandering contained in the signal 13 is attenuated. Therefore, even when an exciting frequency which is sufficiently higher than the frequency of commercial power supply is used, the influence of the harmonic component generated by the distortion of the frequency noise of commercial power supply can be suppressed and the slurry noise produced by a slurry fluid can be reduced.
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