Research On Non-invasive Weak Current Sensor Based On Tunneling Reluctance Effect

With the steady and rapid evolution of science and technology,data acquisition has become increasingly significant in today’s era of internet-based information.In recent years,especially with regard to the acquisition of weak signals,large difficulties exist during the process of acquisition;however,this type of data holds great value when applied practically and is used extensively in various fields.With the deployment and promotion of smart grids and pervasive Io T networks for electric power,current sensing technology plays a critical role in the power system.Ground loop currents are generated during the operation of power cables,which are normally at a very low level,on a milliampere or microampere scale.However,when faults occur,these currents can become very high,posing a threat to the safe and stable operation of power cables.Thus,investigating how to safely and reliably detect ground loop currents through current sensing technology is an important issue.However,existing research on current sensors has mainly focused on measuring large currents,with relatively little attention paid to the detection of small currents.Furthermore,sensors are highly susceptible to interference factors,and traditional magnetic core closed-loop structures are difficult to disassemble.Tunnel magnetoresistance(TMR)current sensors have many advantages,such as high sensitivity,high response frequency,and strong anti-interference ability.This paper focuses on the study of a non-invasive weak current sensor based on the tunneling magnetoresistance effect.We design a two-piece square corner magnetic core structure,and employ a regulated circuit with an isolation power supply and a floating ground common-mode bootstrapping structure instrument amplifying circuit to accurately measure the weak current of the ground loop.The paper firstly compares the advantages and disadvantages of various current sensors,determines and analyzes the current measurement method of TMR sensors,establishes a transfer function to compare and analyze the characteristics of open-loop and closed-loop structures,and determines the use of a TMR current sensor that combines an externally applied magnetic core structure with a closed-loop structure for research.Relevant linear magnetic field sensor chips were investigated,and chip selection was based on the requirements of the designed current sensor,with chip performance tested accordingly.The structure size of the magnetic core was simulated using finite element simulation software,the structural parameters of the magnetic core were determined,and error simulations were analyzed in response to existing interference factors.The paper designs the signal processing circuitry for the TMR current sensor.Firstly,an isolated power supply design is used for the power module,and voltage transformation and stabilization are performed.The signal conditioning circuit adopts a high power suppression ratio power supply design,including a front-end instrument amplification circuit,a secondary amplification circuit,a filtering circuit,a feedback circuit,and a sampling circuit.Based on the designed circuit schematic and the selected chip,the magnetic core gap width size and PCB board are determined and designed,with the magnetic core gap width size determined to be 4.2mm,and physical order placed for the magnetic core and PCB board.Finally,the performance of the designed TMR current sensor is tested,with sensitivity,range,and linearity tested.After analyzing the test data,the non-invasive weak current sensor based on the tunneling magnetoresistance effect designed in this paper has a range of 0-20 m A,a sensitivity of 19 m V/m A,and a linearity of 0.62%.In conclusion,the paper analyzes some factors that cause sensing test errors and provides solutions.The designed two-piece magnetic core structure in this paper meets the requirements of a detachable sensor and expands the application scenarios of sensors.Additionally,the TMR sensor for weak current measurement has a wide range and accuracy,which can accurately detect ground loop currents.