| 摘要 |
PURPOSE:To eliminate the influence of a slurry noise and differentiation noise and to obtain an electromagnetic flowmeter which has a stable zero point by varying a higher frequency between two frequencies from an exciting means relevantly to the slurry noise. CONSTITUTION:The exciting circuit 13 of an electromagnetic flowmeter supplies exciting currents of a 1st frequency and a 2nd lower frequency to an exciting coil 12 under the control of a timing circuit 18 to apply a magnetic field to fluid to be measured by the conduit 10 of the flowmeter through the coil 12. Further, electrodes 11a and 11b in the conduit 10 detect a signal voltage and a preamplifier 14 removes a common voltage and performs impedance conversion to send its output to a coupling point 15. The output voltage at this coupling point 15 is supplied to an LPF 19 and an HPF 20 through low-pass filters 16 and 17 under the control of the circuit 18. The outputs of those LPF 19 and HPF 20 are summed up at an addition point 21. Further, a noise discriminating circuit 24 controls the circuit 18 to vary the higher frequency between those two frequencies relevantly to the slurry noise.
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