Research On Current Detection Technology Based On AMR Magnetic Sensor

With the rapid development of industry,current detection technology has gradually matured.Currently,current sensors are generally designed through electromagnetic characteristics.After the magnetic field is detected,the current can be obtained according to the linkage relationship between electricity and magnetism,thereby achieving electrical isolation.The purpose of this article is to design a current sensor with high accuracy and strong anti-interference ability based on this principle.Hall current sensors have low cost,so they are widely used in industrial current detection.However,the Hall element has low sensitivity,high noise,and poor temperature stability.In addition,the Hall chip must be matched with a magnetic ring to amplify the magnetic field.There is a serious magnetic leakage problem,which results in weak anti-interference ability and poor reliability,so it does not meet the requirements of laboratory current measurement.In response to the above problems,a non-contact AMR zero-flux current detection system was designed in the paper through the overall optimization of the circuit and magnetic circuit.AMR magnetic sensor was adopted as the sensitive element of the system,because it has high sensitivity,low noise and high temperature stability.At the same time,the hollow ferrite ring core was used as the magnetic shield to replace the traditional magnetic ring,which improves the anti-interference performance and realizes high-precision current detection.The main work completed in this article is as follows:1.A magnetic sensor based on AMR was designed.In accordance with the design requirements of chip-level size,high sensitivity,low noise,and low power consumption,the KMZ51 chip was selected as a magnetic sensor probe to convert the induced magnetic field into a voltage signal.The signal conditioning circuit was designed around KMZ51,including a magnetization reversal module and an electromagnetic feedback module: a pulse reversal circuit was designed to periodically magnetize the internal magnetic resistance of the KMZ51 so that the KMZ51 outputs an AC signal,which can improve the sensitivity of the sensor.After high-pass filtering,the DC offset of the bridge can also be eliminated.The lock-in amplifier uses AD630 as the core,which can demodulate the AC signal and improve the signal-to-noise ratio.The electromagnetic feedback unit is mainly realized by a closed-loop negative feedback structure,and the compensation coil is the core of the negative feedback.When the system is balanced,the magnetic field generated by the compensation coil cancels the magnetic field to be measured,which can eliminate the sensitivity temperature drift.In addition,a digital platform based on STM32 was designed and applied to AMR magnetic sensors to realize the measurement and display of magnetic fields.2.On the basis of magnetic sensor,the AMR zero flux current detection system was designed,which mainly includes two parts: magnetic circuit and circuit.In the magnetic circuit part,a hollow ring of manganese zinc ferrite was designed as the magnetic shield.The AMR chip is located in the gap inside the magnetic core,which reduces the magnetic error caused by the interference magnetic field.The software Ansoft Maxwell was used to simulate the magnetic core.By comparing the deviation rate of the magnetic induction intensity at the gap of the core when the primary wire is placed eccentrically,the core parameters were optimized,and the anti-interference performance of the hollow ring was verified to be better than the magnetic ring.In the circuit part,a closed-loop negative feedback structure based on PI compensator was designed,which eliminates the error caused by hysteresis effect and temperature drift,and improves the linearity.At the same time,the magnetic circuit and circuit model of the current sensor were established,and the transfer function of the system was deduced,and finally the relationship between the system steady-state error and the PI compensator parameters was obtained.3.The experimental platform was established to test the key performance indicators of magnetic sensors and current sensors.The magnetic sensor was calibrated by a Gauss meter,and the results show that the linearity reaches 0.7%,the sensitivity reaches 3.56V/Gs,and the short-term stability is good.The frequency spectrum analysis of the magnetic sensor shows that the 1/f noise level is about 6 nT/ Hz @1Hz.The test results of the AMR current sensor show that the current detection range is ±50A,the frequency band measurement range is DC-100 kHz,the accuracy is better than 0.7%,the anti-interference performance is excellent,and it can be used for laboratory current detection.