Weak Current Detection And Vector Magnetic Field Sensing Based On Magneto-optic Probe

Electromagnetic detection plays a very important role in the fields of smart grid construction and national defense military construction.With the improvement of transmission technology and power grid level,the traditional electromagnetic current transformer and magnetic field detection technology exposed a series of problems,which can not meet the needs of current and magnetic field detection.The optical current sensor and optical magnetic field sensor have the advantages of good insulation,anti electromagnetic interference,small volume and large measurement dynamic range,which adapts to the development of intelligent and digital sensors and has a great development prospect.Magneto-optical crystal materials have the characteristics of large Verdet coefficient and high sensitivity.Therefore,the optical current sensor and optical magnetic field sensor based on magneto-optical crystal are studied in this paper.In order to ensure the normal operation of the power system,it is necessary to monitor the leakage current and other weak current signals of electrical equipment in real time.There are problems such as poor signal-to-noise ratio when measuring weak current signals.Therefore,this paper analyzes the influencing factors of current sensing based on magneto-optic crystal,and the influence of light source,photodetector,depolarizer and other devices on current measurement is studied.The structure of optical current sensor based on magneto-optical crystal system is improved.When measuring the power frequency signal,the output signal of the sensor is multi-stage amplified and filtered.In order to suppress the noise,FFT transform is applied to the signal by use of frequency analysis.Low frequency noise is the main reason for the errors in DC signal measurement.In order to improve the accuracy of DC signal measurement,the light source is modulated from DC signal to AC signal firstly.On the principle of phase-locked amplification,the digital lock-in amplifier is used to detect the weak DC signal,which improves the measurement resolution.The experimental results show that the sensor has high sensitivity,the minimum power frequency current signal that can be detected is less than 1 mArms and the resolution of DC signal measurement is higher than 1 mA.In this paper,the principle of vector magnetic field sensor based on magneto-optical crystal is studied.Two dimensional magnetic field sensing probe device based on magneto-optic probe is designed and the sensitivity of magneto-optic probe is also calibrated.Two-dimensional magnetic field sensor measurement system is built.The two-dimensional magnetic field sensor based on magneto-optical crystal is applied to magnetic field measurement,and magnetic field signal detection less than 1uT can be realized in the measuring system.The measurement of two-dimensional magnetic field is realized preliminarily.It is proved that the vector magnetic field sensor based on magneto-optical crystal can measure the weak magnetic field signal and lays a foundation for the application of the optical magnetic field sensor based on magneto-optic probe in three-dimensional magnetic field measurement.