The basic operating principle of an Electromagnetic Flow Meters is based on Faraday’s Law. Faraday’s law states that, when you move a conductor perpendicular through a magnetic field, a voltage will be induced proportional to the velocity of the conductor. In the case of an Electromagnetic Flow Meter a magnetic field is created by a set of coils which are encapsulated and rigidly retained in the meter flow tube, and when a conductive liquid moves through that magnetic field, a pair of electrodes which are in contact with the conductive fluid as it moves through the magnetic field measures the voltage induced by the movement of the liquid. The measurement is independent of conductivity (uS/cm) changes in the liquid as long as it remains above the minimum threshold. However, the minimum threshold varies greatly by manufacture design of the Electromagnetic Flow Meters, and may be as low as 3.0 uS/cm and as high as 30.0 uS/cm. A combination of flow tube and converter design causes this variance. Coil winding and precision, liner uniformity, electronics signal processing, all contribute to this variance.
The relationship between the liquid velocity and the induced voltage is expressed in a meter K-factor. The meter K-factor is unique to each and every meter and is documented during a calibration flow test completed prior to the meter shipment. The calibration flow test should be done under traceable standards such as NIST, JIS, or ISO to ensure the validity and accuracy of the meter K-factor. With the K-factor established a highly accurate volumetric flow measurement is calculated by multiplying the cross sectional area of the flow tube by the measured liquid velocity. This volumetric relationship can then be converted to various engineering units and the flow meter converter can then retransmit this information with via a 4-20 mA current signal and / or scaled or conditioned pulse. An optional integral LCD Indicator/Totalizer is available to locally display and totalize in whatever engineering units that are available in the meter programming.
