The basic principle of mag meter is faraday law of electromagnetic induction. It means when a conductor cuts magnetic movement in a magnetic field, both sides of the conductor will produce induction electromotive force named E :
E=KBvD （1）
In this equation, K is instrument constant; B is intensity of magnetization（T）; V is the average speed of conductor’s movement m/s; D is the bore size of piping（m）;
The principle of mag meter
The
mag meter is composed of two parts called flow sensor and converter.
When testing the flow, conductive liquid plays a role as a conductive metal bar of faraday experiment. It passes through a magnetic field which is perpendicular to the direction of flow at average speed v. The flowing of conductive liquid induces the voltage which is in proportion to average flow speed in the measuring electrode. The induced voltage signal E is detected by a pair or more than a pair of the electrode which has a direct contacting with the liquid.
According to the volume of flow, the discharge formula is
Q=1/4π D2v（2）
From the formula (2), are we come to know Q is in proportion to V as one—to—one function. Thus, E and Q is one—to—one function as well. That is, when induced voltage E is detected, that we can get volume flow Q of the medium.
The measured induced voltage E will be sent to the converter by cable. Through the intelligent process, it will be displayed on the LCD or turned into standard signal 4～20mA to be output.
The characteristics of mag meter
(1)The is no resistant component within the measuring pipe and additional pressure loss, so it is not easy to have a blockage. That has a prominent energy saving significance.
(2)There is no movable part within the measuring pipe, so it is hard to be abrasive. As a result, the service life of the sensor is long.
(3)The straight length that flow sensor needs are rather short, which is convenient to be installed.
(4)Having chosen the electrodes and lining material rationally, it is corrosion preventive and is standing wear and tear.
(5)There is bidirectional measuring system which can measure the flow forward and reverse.
(6)The measurement of the flow is volumetric flow, which is free from the influences of density、dynamic viscosity、temperature、pressure and conductivity change.
(7)The induced voltage signal of the sensor is in leaner relation with average flow rate. It has high accuracy（±0.3～-0.5％）and wider range ratio（1：150）.
