To enhance accuracy in the measurement of flow rate by neglecting a current A in the vicinity of the pipe wall on the receiver side where the measurement accuracy is low and determining a current distribution data C in the vicinity of the pipe wall from a current distribution data B detected with high accuracy from a part other than the vicinity of the pipe wall and then calculating the flow rate from the current distribution data B and C.
In the region Xm remote from the pipe wall, effect of noise reflected on a boundary face is suppressed and a normal current distribution B is detected. A current distribution indicator/corrector sets a normally detected current distribution B positive and extrapolates the positive current distribution B on the region Xm side thus determining a current distribution C by numeric analysis. The current distribution is approximated by a quadratic or cubic curve by a method of least squares, for example, and the current in the region Xm is extrapolated using that curve to obtain a current distribution as shown by a dashed line C. A flow rate calculator calculates the flow rate from the corrected current distributions b and C according to a specified formula.
YAZAWA SETSUO
OKAMURA TOMOYOSHI
KOGA MASAAKI
