Intelligent electromagnetic flow meter adopts low voltage micro power consumption measurement principle

Intelligent electromagnetic flowmeter With the development of electronic technology and microelectronics, the market of electromagnetic flowmeters has been gradually perfected, and with the advent of low-voltage micro-power large-scale integrated circuits, the application of electromagnetic flowmeters has brought another broad Prospects.

This paper analyzes and studies the measurement principle of a low-voltage micro-power battery-powered electromagnetic flowmeter abroad, mainly in the following aspects:

a. The theoretical basis of the low voltage micro power electromagnetic flowmeter;

b. Transmitter structure design of low-voltage micro-power electromagnetic flowmeter;

c. Low-voltage micro-power electromagnetic flow meter calibration analysis.

1 Intelligent electromagnetic flow meter working principle According to Faraday’s law of electromagnetic induction, when a conductor moves in the magnetic field to cut magnetic lines of force, induced electric potentials e are generated at both ends of the conductor, if B, L, and V are mutually perpendicular;

Then: e = BLV; (B, L, V are magnetic field magnetic induction, conductor length and moving speed, respectively)

Applied to electromagnetic flowmeters are: (D is the pipe diameter) then the volume flow Qv can be expressed as:

As can be seen from the above equation, the volume flow rate Qv is linearly related to the induced electromotive force e and the inner diameter D of the measuring tube, and is inversely proportional to the magnetic induction intensity B of the magnetic field, regardless of other physical parameters. This is the principle of electromagnetic flowmeters measuring the volumetric flow of conductive liquids.

The main characteristics of the electromagnetic flowmeter: The transmitter has a simple structure and no moving parts. In the measurement process, it is not affected by the measured medium temperature, viscosity, density, and conductivity (in a certain range); the range is extremely wide. It is only proportional to the average flow velocity of the measured medium, but independent of the flow state (laminar flow, turbulent flow) under axisymmetric distribution, and the reaction is sensitive and linear.

It can be seen that it is appropriate to further develop the electromagnetic flowmeter as a low-voltage micro-power electromagnetic flowmeter. However, in the low-voltage micro-power state, battery power is generally used, so the problem of large power consumption of the excitation circuit system needs to be solved. On the one hand, the power consumption of the excitation circuit system is required to be reduced, and on the other hand, sufficient flow signal (induction electromotive force) is required. e). To meet these requirements, the transmitter structure of the excitation circuit system must be solved in the design.

2 Excitation Circuit System Transmitter Structure Analysis Electromagnetic flowmeter transmitter is mainly composed of measurement conduit, excitation system, electrode and interference adjustment mechanism. In order to make the sensor work stably and accurately and accurately sense the flow signal, it must be seriously considered in the structure.

In order to reduce the amount of electric energy consumed by the excitation coil, a special structure was created based on the magnetic field principle of the excitation coil. High-quality super-magnetic permeability ferrite was selected as the excitation coil core (ultra-high permeability nickel-zinc NiZn ferrite μi>12000).

3 Intelligent electromagnetic flowmeter excitation signal processing method The electromagnetic flowmeter magnetic field is obtained through the excitation coil. At present, three-valued low-frequency square-wave excitation forms are used (see Figure 3).

The low-voltage micro-power electromagnetic flowmeter adopts a high-precision double-integration analog-to-digital conversion, which has a good elimination effect for various kinds of sharp pulses and AC power frequency interference. In particular, in the field of excitation, a ternary low-frequency square wave with good zero stability and strong anti-interference ability is adopted, which can well reduce the mutual interference between the positive and negative periods. In addition, the flow meter is used to reduce power consumption. With magnetizing inrush current to enhance the strength of the excitation magnetic field, the performance and effect of the treble-frequency low-frequency square-wave excitation are achieved.

4 Flow signal processing method 1) The flow meter adopts 6B68-0031 low-voltage micro-power large-scale integrated circuit MPU (Microprocessor Unit) microprocessor produced by Hitachi, Japan, as the central controller design solution, the CPU in the chip controls the entire instrument Operation, combined with the 74HC02A and SL130, completes the calculation and storage of the flow signal and the control of the excitation signal function, etc.; the output has functions such as the instrument analog signal (current signal) output and frequency output.

2) The computer's internal CPU central processor processes the data signals, controls the software support, and performs computation and control of the flow data. Measure the induced electromotive force e received by the electrode in the pipe segment, first amplify the weak signal received by the variable gain preamplifier, and then perform the first stage signal amplification, and the amplified signal is A/D converted into the CPU micro The processor also sends the processed flow data result to the display for display value, and in the intelligent design, the CPU microprocessor performs remote data transmission with the pulse signal and the digital signal (data flow) in the external I/O interface circuit. .

5 Analysis of Smart Electromagnetic Flowmeter Calibration Status According to the technical parameter declaration of the product (DN100), refer to the water meter and electromagnetic flowmeter verification procedures, and verify it in the laboratory and the use site after installation of the product.

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