Measurement system output values were recorded when the current of the coil is increased by 15 mA interval at the range from -300 mA to 300 mA. Fig. 3 shows the calibration curve of the measurement system. It is apparent that the output of the measurement system is increased with the increase of the current and the measurement system shows a good linearity, which is in agreement with the above analysis result (Eq.(5)) in Section 2. The linear relationship between the output of the measurement system and electric current of coil also shows the feasibility of the proposed measurement system. Fig. 3 also shows that the proposed electric current measurements system cannot only measure the current intensity, but also the current direction.