Research On The Sensor Technologies Of Electromagnetic Flow Measurement In Partially Filled Pipes

The flow measurement in the partially filled pipes is one of the most important technology for implementing monitoring to the flow of urban sewage discharge, agricultural irrigation and other fields. Because the level is changing, Both the flow rate and the fill height need be measured to calculate the flow in the partially filled pipes. With simple structure and high precision, without throttle element and pressure loss, the electromagnetic flowmeter is suitable for flow measurement in the partially pipes. This thesis researches on the key technologies about the electromagnetic flowmeter in the partially filled pipes (EMF-PF), as follow:I. Research on the EMF-PF filled height measurement.The fill height measurement is key for EMF-PF to measure the flow in partially filled pipes. Presently, most EMF-PF adopt a special level gauge, such as capacitance type level gauge, magnetostriction type level gauge and micromanometer etc., to measure the fill height in partially filled pipes. It is difficult for EMF-PF to measure the flow rate and the fill height in the partially filled pipes synchronously using the special level gauge.There is no special level gauge by measuring the liquid conductance between the sensor measurement electrodes to get liquid level. However, this method can not be used on condition that the liquid conductivity is unconstant. This thesis designs a new method and sensor to measure the fill height in the partially filled pipes unaffected by liquid conductivity, and researches on the sensor level measurement characteristics.II. Research on the structure of EMF-PF sensor.Based on the new level measurement technigue, This thesis presents a kind of new EMF-PF sensor for the flow measurement in the partially filled pipes.On the new sensor pipe bottom, one pair of the electrodes is set as the signal injection electrodes that inject the AC signal used to determine liquid level. The measurement electrodes alternate duties, sensing both the flow velocity and fill height signals. According to this presentment, the thesis designs two kinds of EMF-PF sensors, one with a pair of arc electrodes set as the measurement electrodes and another with a group of multi-electrodes in parallel connection set as electrodes, to measure the flow in the partially filled pipes. By finite element method, this thesis researches on the level measurement features of them.III. Research on the EMF-PF flow measurement and the sensor weight function.Electromagnetic flowmeter is based on Faraday's law for the fluid flow measurements. It is different for the liquid flowing in the magnetic field to generate induced potential comparing with solid conductors. According to the Shercliff's weight function theory, the weight function expresses the contribution ability to the EMF sensor signal for the fluid microelement flowing in the magnetic field. So it is necessary to research on the weight function of the EMF in order to obtain the sensor characteristics. This thesis first studies the influence created by arc electrodes on the EMF weight function. Then, the thesis studies the weight function of EMF-PF in the various fullness degree and gives the map of EMF-PF sensor with a pair of arc electrodes. The results proves that the flow measurement characteristic of the arc electrodes sensor is nonlinear. The research results on the sensor features and weight function provide a theoretical basis for optimal design of the EMF-PF sensor.IV. Research on the implementation technology of the EMF-PF.This thesis designs the key circuit and data processing scheme of the EMF-PF and designs the EMF-PF prototype. The experimental platform is created for flow measurement in the partially pipes.The calibration experiment proves that the flow measurement precision of the EMF-PF prototype can reach 1.3% in the partially filled pipes and 0.4% in the full pipes.