Study On The Double-loop Magnetic Detector And The Magnetic Shielding Effectiveness Of The Current Comparator

The work in the paper is supported by the National Natural Science Foundation of China,(No. 51177061). Now the research about the dc current comparator based on the magnetic modulator is confronted with two major problems. One is the channel-closing problem in the multi-channel comparator for dc current, and the other is the calculation method of the shielding effectiveness of current comparator.As the false balance point existing in the magnetic modulator, the channel-closing problem may happen in the multi-channel comparator for dc current based on the magnetic modulator. In order to solve the channel-closing problem thoroughly, the design of the double-loop magnetic detector is presented. The double-loop magnetic detector consists of the magnetic amplifier loop and the magnetic modulator loop. The output signal of the double-loop magnetic detector possesses not only the high sensitivity of the magnetic modulator output signal, but also the monotonic feature of the magnetic amplifier output signal. The input-output characteristic of the experimental model of the double-loop magnetic detector is measured; and the Simulink model of the double-loop magnetic detector is built. The results of the experiment and simulation prove the input-output characteristic of the double-loop magnetic detector is better than the magnetic modulator one. And the better open-loop characteristic is beneficial to the solution of the channel-closing problem in the multi-channel comparator.In order to ensure the proper function of the current comparator, the magnetic shield should be installed to reduce the influence of the magnetic interference. But currently the calculation method of the shielding effectiveness of current comparator for radial direction magnetic interference is not accurate enough. And the research of the double-layer magnetic shielding effectiveness is more lack. So based on the magnetic circuit analysis principles, the more accurate methods of the shielding effectiveness for the single-layer and double-layer magnetic shields are presented. And the Ansoft finite element analysis is used to prove the accuracy of the calculation method.