Research On Small Current Sensor Based On Tunnel Magnetoresistance Effect

With the continuous increase of voltage level and capacity of power system,it is of great significance to timely and accurately knowing the insulation of high-voltage electrical equipment to maintain the safe and stable operation of power system.Insulation monitoring needs to measure m A level small current.Traditional magnetic modulation sensor and optical fiber current sensor have the disadvantages of large volume and complex structure,which are not suitable for the development of intelligence and portability.Tunnel magnetoresistance(TMR)current sensor has the advantages of low power consumption,high integration and high sensitivity,and has broad development prospects in the field of current measurement.Therefore,this paper studies the detection of TMR current sensor in small current scene.Firstly,the tunneling principle and working mechanism of TMR chip are analyzed.Considering the measurement range and design difficulty,the open-loop structure is selected for small current detection.Aiming at the temperature drift of TMR current sensor sensitivity,a hardware compensation circuit based on thermistor is designed,and a software compensation method based on cubic spline interpolation fitting is proposed.Secondly,the TMR low current sensor is designed from three aspects: component selection,magnetic gathering ring design and circuit design,and the multi-dimensional company TMR2901 chip is selected.In the Maxwell finite element simulation software,the magnetic field uniformity coefficient and the shielding efficiency of the magnetic gathering ring are designed;the signal reading circuit is designed by using the instrument amplifier with three operational amplifiers.Finally,the performance of the designed small current sensor is tested.The designed TMR low current sensor can measure the current of 0～±250m A,and the sensitivity is 9.994V/A.The hardware compensation circuit and software compensation scheme can reduce the sensitivity temperature drift coefficient of the sensor from 1793.9ppm/℃ to 387.9ppm/℃ and106.3ppm/℃.The designed TMR small current sensor can realize the accurate measurement of small current and meet the needs of small current measurement in power system.