Views: Release Time:2019-08-14
Electromagnetic Flowmeter (EMF) is a new type of flow measuring instrument that was developed rapidly with the development of electronic technology in the 1950s and 1960s. The electromagnetic flowmeter is made according to Faraday's law of electromagnetic induction, which is used to measure the volumetric flows of conductive liquids. Due to its unique advantages, electromagnetic flowmeters have been widely used in the flow measurement of various conductive liquids in industrial processes, such as various acid, alkali solutions, salt solutions and other corrosive medium and various slurry flows.
Structurally, the electromagnetic flowmeter consists of an electromagnetic flow sensor and a converter. The sensor is mounted on an industrial process pipe. Its function is to linearly convert the liquid volume flow value flowing into the pipe into an induced potential signal and send this signal to the converter through the transmission line. The converter is mounted not far from the sensor, it amplifies the flow signal sent by the sensor and converts it into a standard electrical signal output proportional to the flow signal for display, accumulation and regulation control.
Electromagnetic flowmeter working principle
(1) Measurement principle
According to Faraday's law of electromagnetic induction, when a conductor moves in a magnetic field to cut a magnetic line of force, an induced potential e is generated at both ends of the conductor, the direction of which is determined by the right-hand rule, the magnitude and magnetic induction of the magnetic field B, and the conductor is within the magnetic field. The length L is proportional to the speed u of the conductor. If B, L, and u are perpendicular to each other, then e= Blu (1-1)
Similar to this. In a uniform magnetic field with magnetic induction B, a non-magnetic tube with an inner diameter D is placed perpendicular to the direction of the magnetic field. When the conductive liquid flows at the flow velocity u in the tube, the conductive fluid cuts the magnetic field lines. If the magnetic field is perpendicular to both ends of the diameter of mounting a pair of electrodes (Chart-1) on the pipe cross-section can be proved, as long as the flow velocity distribution axially symmetrical distribution duct, also induced electromotive force is generated between the two Laid electrodes:
Where is the average flow rate on the section of the pipe. The volumetric flow rate of the pipe thus obtained is:
It can be seen from the above formula that the volume flow rate qv is linear with the induced electromotive force e and the inner diameter D of the measuring tube, and inversely proportional to the magnetic induction intensity B of the magnetic field, independent of other physical parameters. This is the measurement principle of electromagnetic flowmeter.
It should be noted that in order for the formula (1-3) to be strictly established, the measurement conditions must satisfy the following assumptions:
1 The magnetic field is a uniformly distributed constant magnetic field;
2 the flow velocity of the measured fluid is axially symmetrically distributed;
3 The liquid to be tested is non-magnetic;
4 The conductivity of the liquid to be tested is uniform and isotropic.