Design Of GMR Current Sensor Based On CAN Bus

In this paper,a electric current sensor with a CAN bus is designed and realized,in which the current could be measured and transmitted through the CAN bus interface.The real-time measurement of the current signal is realized,and the isolation transmission is realized.The defect that the output signal of the current sensor is easily disturbed and the transmission distance is near is solved.The designed current sensor could be used in automobile electronics,smart grid,intelligent meter and so on.The whole design consists of two parts: the current sensor based on the giant magneto resistance sensor and the data transmission module of the CAN bus and the former is the focus of the study.The current sensor is mainly divided into two structures: open loop and closed loop.The open loop current sensor circuit is simple,but with a disadvantage of low accuracy of measurement.Closed loop current sensor has high accuracy and stability,Therefore,the closed loop structure is adopted in the design.The hardware structure of the whole current sensor is mainly composed of five parts: magnetic signal acquisition module,amplifying circuit,power amplifying circuit;feedback circuit and CAN bus data transmission module.The main content of the software design is the CAN bus collects and transmits data.The thesis expounds the GMR principle and introducing the basic principles of measuring electric current by magnetoresistance senser.By building up a system model of the closed loop type current sensor and analyzed the negative feedback which provides the characteristics and errors of the sensor,the method of reducing error,in order to improve the accuracy and reduce the measurement errors.Introduces the classification of magnetic materials and determing magnetic air gap;the AD620 is choosed as amplifier circuit,the TDA2030 is choosed as power amplifier circuit.In this work a method to reduce the zero drift is also proposed.The CAN bus transmission module use the STM32 chip as the CAN controller unit and use the TJA1050 as the CAN transceiver.The STM32 put forword by Italy semiconductor company,it has the advantages of rich resources and simple circuit design,so it is widely used.The module is used to get voltage of the GMR electric current senser and send voltage data to the computer,realized the remote monitoring of electric current.The measurement range,sensitivity,linearity and accuracy of the current sensor are tested by using the laboratory platform.The range of the designed current sensor is 5A,the accuracy is about1%,and the linearity is better than 0.05%.It has good temperature characteristic and the overallperformance is better than the general current sensor.