Research On Measurement Technology Of Electromagnetic Flow-meter

Electromagnetic flow meter is a flow measurement instrument based on The Faraday's law.Compared with other flow measurement instruments,there are no moving parts in the pipeline,and the pressure loss is small,also with high sensitivity.The greatest advantage is that the measurement accuracy is not affected by the fluid density,pressure and temperature.It's widely used in urban sewage treatment,chemical,food and other industrial sites.To achieve the syrup,pulp,mud and other conductive fluid flow measurement.The traditional electromagnetic flow meter's detection electrode is easy to corrosion and wear,because contact with the liquid.It's also difficult to pick up the flow-rate signal,because the low-conductivity.So there are more difficulties and higher requirement in circuit design.Capacitive electromagnetic flow meter is also based on The Faraday's law.The biggest difference with the traditional electromagnetic flow meter with adopted capacity coupled mode to detect the flow-rate signal.This structure not only effectively protects the detection electrode,reduces the noise component,also improve the signal stability and measurement accuracy,and reduce the sensor internal resistance.This paper is based on the existing research in the laboratory.Firstly,described the theory of electromagnetic flow meter and analyzes the structure of the sensor.The characteristics of the flow signal and its noise components are analyzed emphatically.Then,by analyzing the advantages and disadvantages of kinds of excitation methods,selected the 200 Hz rectangular wave as the excitation signal,and used the simulation software Ansoft Maxwell14.0 to analysis the magnetic field distribution,optimization the structure of sensor.Use the 32-bit microprocessor STM32F407VET6 as the control chip.Combine with constant current circuit that based on the LDO and H bridge circuit to generate the magnetic field.As the same time,based on the structure of capacitive electromagnetic and the flow-signal features,use the bootstrap follower circuit structure to improve the input impedance of the signal detection circuit,and pick up the flow-rate signal.The flow signal processing circuit utilizes the differential amplification characteristic of the instrumentation amplifier,combines the rotation capacitance filter and the precision rectifier circuit to process the flow-rate signal.Finally,used the tap water as the object to be measured,through the experimental verification,effectively detected the flow-rate signal.Successful established the relationship of the output voltage amplitude and the instantaneous flow-rate,Validated the feasibility of the project.