Structure type: solid flowmeter consists of electromagnetic induction air flowmeter and converter. The controller is installed on the whole process pipeline of industrial production. Its function is to linearly convert the total flow value of liquid volume flowing into the pipeline into the induced potential difference data signal, and send the data signal to the converter according to the coaxial cable. The converter is installed in the area not far from the controller. It enlarges the total flow data signal sent by the controller, and converts it into a standard electronic signal output proportional to the total flow data signal to display information, accumulate and adjust the operation. （1） Basic principles of measurement

According to the basic law of magnetic effect of Faraday current, when an electric conductor is moving in the magnetic field and laser cuts the magnetic induction line, the induced potential difference e is caused on both sides of the electric conductor, and its orientation is determined by the right hand. Its size is directly proportional to the magnetic induction intensity B of the magnetic field, the length L of the electric conductor in the magnetic field and the fitness movement rate U of the electric conductor. If B, l and u are perpendicular to each other, then

e＝Blu(3－35)

E = BD (3-36) is similar to this. In a symmetrical magnetic field with magnetic induction intensity B, a non-magnetic pipe with nominal diameter D is placed in the direction of vertical bisector magnetic field. When the conductive liquid flows with water flow rate u in the pipe, the conductive fluid mechanics will cut the magnetic induction line by laser. If a pair of electric stages are installed on both sides of the diameter of vertical bisector magnetic field on the cross section of Integrated flowmeter, it can It can be proved that if the water flow in the pipeline is axisymmetric, the induced electromotive force will be generated in the middle of the two stages:

Where, is the average water flow on the cross section of the pipeline, so the total volume flow of the pipeline is required to be:

qv＝πDUˉ＝（3－37）

It must be shown that in order to establish formula (3-37) rigorously, the following assumptions must be taken into account in the measurement standard: from the above formula, it can be seen that the total volume flow QV is linearly related to the induced current E and the nominal diameter D of the measuring tube, inversely related to the magnetic induction intensity B of the magnetic field, and irrelevant to other main physical parameters. This is the basic principle of measurement of pressure transmitter

① The magnetic field is a stable field with uniform distribution;

② The water flow of measured hydrodynamics is axisymmetric;

③ The measured liquid is non-magnetic;

④ The conductivity of the measured liquid is symmetrical and anisotropic. （2） Excitation method

The excitation method is the method to create the magnetic field. As we know from the above situation, in order to make formula (3-37) strictly established, one criterion that must be considered is to have a uniform and stable magnetic field. Therefore, it is necessary to select a suitable excitation method. At present, there are three excitation methods: DC excitation, communication sulfuric acid flowmeter and high frequency waveform excitation

1. DC excitation

In DC excitation method, DC current is used to create magnetic field or electromagnet is selected, which can create a stable and symmetrical magnetic field. The great advantage of this kind of DC excitation intelligent transmitter is that it is not seriously affected by AC current magnetic field, so it can The harm of self induction phenomenon in liquid is ignored. However, it is easy to make the electrolyte solution liquid in the measuring pipe be electrodialized by DC magnetic field, that is, the electrolyte solution is electrolyzed in the electrostatic field, resulting in positive air anion. Under the effect of electric field force, the air anion runs to the positive level, and the positive ion runs to the negative level. In this way, it will cause The positive and negative electrodes are surrounded by the opposite polarizing ionization, which seriously endangers the normal operation of the pressure transmitter. Therefore, DC excitation is generally only used to measure non electrolyte liquid, such as shape memory alloy