Non-contact Weak Current Detection System Based On Systemic Scaling Method And Its Application

As a method of functional medical detection, bio-impedance measuring technology attracts more and more attentions of medical researchers because of its convenience, harmlessness and abundance of functional information. The development of this technology makes it possible for researchers to explore the meridians' position and essence with its bio-impedance characteristic. As a type of non-contact measurement, the magnetic detection bio-impedance measurement has following advantages: the measuring circuit has no influence to the test target; the position of sensors are easy to arrange and adjust; the amount of independent measured data can be increased effectively by changing the position of coils in order to improve the quality of imaging and measuring. As same as the universal linear measure system including exciting sources, however, the accuracy of magnetic detection bio-impedance measurement system is confined by the accuracy and the stability of exciting sources. Therefore, it's necessary to do some improvements.There are difficulties to improve the amplitude accuracy and stability of the existing exciting sources according to the complicated technology or high costs. In this essay, the scaling method is applied on system level. And the systemic scaling method and lock-in amplifying technology are combined. Thus errors caused by amplitude fluctuation are minimized and requirements for the exciting sources are decreased. This method is able to be applied in usual linear measure systems (including system with non-resistance sensor), which provides with some new ideas and a high level range for improving the measurement accuracy.Aiming at the disadvantages of the existing non-contact weak current detection systems such as inadequate complicated technology, limitation for position of sensors and so on, a new non-contact weak current detection system was designed based on systemic scaling method, which focuses on studying and improving the circuit of measuring function itself. The experiment results show that the system is able to detect currents (minimum 10-5A) effectively with a distance of less than 3cm from the centre of sensor. The system designed also lowers the technology requirement and has less limitation for relative position of sensors and currents to be detected.A high precise multi-channel synchronous current source centering on DDS chip AD9959 was designed to meet the design specification of the high-performance exciting source of bio-impedance measurement system, such as having two or more clock-synchronization output channels with high accuracy and independent phase control between channels. A system based on systemic scaling method and lock-in amplifying technology was also designed as an elementary plan for hardware of magnetic detection electrical impedance measurement system, which was researched rarely. Some simple experiments were carried out with the system, and the result showed that the system can make a qualitative discrimination between different impedance objects.