Electromagnetic flowmeter

A method of measuring a flow rate of a fluid that flows through a measuring pipeline arranged in a controlled magnetic field controlled by a square wave exciting current, comprising the steps of:

• generating a magnetic flux in the controlled magnetic field;
• measuring a density of the magnetic flux generated in the controlled magnetic field;
• generating an electric signal according to the density of the magnetic flux generated in the controlled magnetic field and according to a flow speed of the fluid;
• adjusting the magnetic flux density to a predetermined value by controlling the square wave exciting current;
• measuring the electric signal at predetermined time cycle determined by a frequency of the square wave exciting current;
• and
• computing the flow rate of the fluid based on the measured electric signal and based on the square wave exciting current when the measured electric signal is detected, whereby the flow rate of the fluid can be measured accurately regardless of the fluctuation of the square wave exciting current.

An electromagnetic flowmeter using a square wave exciting current, comprising:

• an exciting coil, arranged out of a measuring pipeline, for generating a magnetic flux in the measuring pipeline in which fluid flows;
• an exciting power source circuit, including a clock circuit for generating a clock signal with a predetermined frequency, for supplying to the exciting coil the square wave exciting current corresponding to the frequency of the clock signal;
• an electromagnetic sensor, arranged out of the measurement pipeline and near the exciting coil, for detecting a density of the magnetic flux generated in the measuring pipeline;
• a magnetic flux control circuit for controlling the square wave exciting current supplied from the exciting power source circuit to the exciting coil, so as to set the density of the magnetic flux detected by the electromagnetic sensor at a predetermined value;
• a pair of electrodes, installed so as to face inside of the measurement pipeline, for detecting an electric signal with a value corresponding to a flow rate of the fluid which flows through the measuring pipeline;
• sampling means for sampling the electric signal detected by the electrodes, in accordance with the frequency of the clock signal generated from the clock circuit;
• compensating means for compensating the electric signal on the basis of a signal supplied from the exciting coil in accordance with the square wave exciting current, so as to eliminate an error in the electric signal due to a fluctuation of the square wave exciting current;
• and
• output means for outputting the electric signal adjusted by the compensating means, by converting the adjusted electric signal to a predetermined signal form.