Yongcai Yang’s research while affiliated with University of Shanghai for Science and Technology and other places

Linear Hall IC can be used for the low price open-loop Hall Effect current sensor thanks to its high sensitivity. However, according to the experimental results, its thermal performance is greatly related to the thermal drift coefficient of linear Hall IC and the gain of the amplifying circuit. In this paper, the thermal drift of the zero offset will be improved by two methods. One is to use two Hall ICs, the thermal drift coefficients of which are similar, to build up a differential amplifying circuit to compensate the common thermal drift of the two Hall ICs. Another one is to add a magnetic core for concentrating the magnetic flux. In this way the gain of the amplifying circuit is reduced by increasing the magnetic flux density passed through the Hall IC. Experimental results show that the thermal performance of the optimized current sensor is reasonably improved by the proposed methods. Keywords— linear Hall IC, open-loop Hall Effect current sensor, thermal drift improvement, thermal drift coefficient, amplifying circuit gain.

In this paper, a new complementary symmetrical structure of using dual magnetic cores for open loop Hall-Effect current sensors is proposed to reduce the influence of the position change of primary current carrying conductor, which cannot be compensated in signal processing circuit. Magnetic field simulations by using Ansoft Maxwell are made to evaluate the influence from the magnetic fields of the core air gap, as the conductor changes its position inside the core. Both simulation and the testing results show that the influence is obviously reduced by a dual cores structure, and the accuracy of open loop Hall-Effect current sensor is improved to ±0.5%. Keywords – dual magnetic cores; primary current carrying conductor position; Magnetic field simulation; open loop Hall-Effect current sensor; accuracy improvement 1. Introduction Current measurement is always one of the most necessary tasks in electrical equipment, especially in power devices [1]. Comparing to other current measuring products, Hall-Effect current sensors enjoy the best price versus performance ratio, low cost, small size and weight, non-contact, galvanic isolation and non-insertion losses, low power consumption, suitable for both DC and AC, high capability of overload, good linearity and accuracy [2, 3]. Though open loop Hall-effect sensors have advantages mentioned above, they only have a common accuracy of ±1.0%, which is relative low compared with that of closed loop Hall-Effect current sensors of ±0.5% (even ±0.2%). The following figure (Fig. 1) shows a brief block diagram of the operating principle of open loop Hall-effect current sensor. Fig. 1 Block diagram of open loop Hall-effect current sensor In a Hall-effect current sensor, the magnetic flux density B generated by the primary current I P under measurement is detected with a Hall-Effect element. The output voltage of the Hall-Effect element is boosted by a high gain amplifier. The output of the amplifier is the final output of the current sensor. There are various kinds of accuracy improving methods. However, most of them locate in the amplification part, and it cannot deal with the errors from the parts that influence the magnetic flux density in the air gap.

In this paper a new split core Hall Effect current sensor based on closed loop principle is introduced. With the split core configuration, the current sensor system can be constructed more conveniently. The signal conditioning circuitry is designed by utilizing closed loop principle in order to improve the measuring accuracy of split core current sensors with low additional costs.