Electromagnetic flowmeter

An electromagnetic flowmeter for measuring the flow rate of a fluid medium including an alternating current magnetic flux generating system positioned to apply said magnetic flux across a section of a pipeline;

• main electrodes mounted on said pipeline section at diametrically opposed locations thereof adapted to sense potentials proportional to the flow rate of the medium in the pipeline;
• at least two pairs of additional electrodes mounted on the same pipeline section on generatrixes of said section of the pipeline which extend through each of said main electrodes and adapted to sense potentials proportional to eddy currents produced in the medium due to magnetic field changes with time;
• and a measuring system including an adder unit having a first input thereof connected to a first pair of said additional electrodes positoned on a first of said generatrixes extending through one of said main electrodes and a second input thereof connected to a second pair of additional electrodes positioned on a second of said generatrixes extending through the other of said main electrodes;
• a first amplifier having the input thereof connected to said main electrodes;
• a first phase-sensitive detector adapted to discriminate a signal proportional to the flow rate of the medium having the input therof connected to the output of said first amplifier;
• a second amplifier having the input thereof connected to the output of said adder unit;
• a second phase-sensitive detector adapted to discriminate a signal proportional to eddy currents having the input thereof connected to the output of said second amplifier;
• and a comparator unit connected to the outputs of said first and second phase-sensitive detectors, said comparator unit being adapted to compare the signals from said main and additional electrodes and provide an indication of the flow rate of said medium.