PURPOSE: To enlarge a detectable max. flow rate to a large extent, by determining the only flow rate value on the basis of constant relation present between each of a plurality of Doppler demodulation frequencies and a flow rate.
CONSTITUTION: Demodulation frequencies fd1, fd2 are normalized by normalization circuits 31, 32. The obtained normalized frequencies F1m, F2m are used in an orthogonal function generating part 33 and passes coordinates (F2m, F1m) while a straight line crossing a graph straight line when the ratio of carrier frequencies is n1 : n2 is generated. A correction amount memory part 35 determines the correction amount ZF1 to a straight line number (i) to apply the same to one input of an adder 38. When the value of an intersecting point is (F2i, F1i), the adder 38 uses an addition result (ZF1+F1i) to generate and output correction demodulation frequency fd.
MIWA HIROHIDE
AMAMIYA SHINICHI
