US 4,059,014 AGranted

Electromagnetic flowmeter

AssigneeHokushin Electric Works, Ltd.

InventorTakashi Torimaru

Life of this patent

Estimating the term…

Loading patent…

Abstract

An electromagnetic flowmeter in which the fluid to be metered is conducted through a flow tube where it intersects a magnetic field established by an electromagnet. A pair of electrodes each having a relatively large surface area are mounted at diametrically-opposed positions in the flow tube whereby the electromotive force induced in the fluid and detected by the electrodes when the fluid velocity profile is non-uniform, is averaged and an electromotive force proportional to average flow velocity is obtained. The electromagnet is energized by a low-frequency wave produced by applying the output of a full-wave rectifier coupled to a commercial power line to the excitation coils of the electromagnet through an electronic switching element that acts to periodically chop the full-wave rectified voltage in accordance with high-frequency pulses whose frequency is higher than the power line frequency, the duty cycle thereof being gradually modulated by a low-frequency wave whose frequency is less than the power line frequency.

Claims7

Dependent claims

In an electromagnetic flowmeter comprising:

A. a flow tube through which a fluid to be metered is conducted to intersect a magnetic field therein which is transverse to the direction of flow and is produced by an electromagnet having excitation coils;
B. a pair of electrodes mounted at diametrically-opposed positions in said tube, said electrodes each having a relatively large surface area whereby the electromotive force induced in the fluid intersecting the field and detected by the electrodes is averaged to minimize the effect of a non-uniform flow velocity on the accuracy of the meter;
and
C. an excitation system for supply current to said coils, said system being constituted by:
a. a power source energized by a commercial a-c power line having a predetermined frequency and providing a direct voltage;
b. electronic switching means interposed between said direct voltage source and said coils;
c. control means to effect an on-off operation of said switching means at a pulse rate which is higher than the frequency of said a-c line;
and
d. means gradually changing the duty cycle of said control means at a low-frequency rate which is less than said line frequency.

6 more elements

Dependencies are inferred from the claim text.