A New Impedance Measurement Method Based On 4-line Current Reversal Technique

Weak signal has two meanings to itself: 1) small amplitude of itself 2) too weak compared to other noise signals to be recognized. Usually, the noises coming from the meters and environment are much stronger than the signal wanted, so the amplification will have more effect on the unwanted noise, and it is then not peculiar that weak signal can not be detected precisely with regular methods. Yet, there are various such signals to be measured as voltage, current, resistor etc in the field of military, production, research, medicine, and so on. So, low level DC signal detection has great importance while full of challenges at the same time.Since nearly all physical signals should be transformed into electric signals before measured, all of which are mostly DC signals, the weak physical signals surely lead to weak electric ones. The measurements of these signals are of profound and great importance in actual application, and the signals include weak voltage, weak current, weak impedance, etc.This thesis labored in the causes of different noises and the mechanisms of different error sources in low level DC signal detection, and then presented corresponding methods to each actual problem. It also summarized some current means dealing with the problem, and proposed a new detection method. After making the 3 different basic impedance measurement methods contrasted, the thesis designed a new weak impedance measurement device based on the 4-line current reversal technique, aiming mainly at the elimination of major error sources, such as thermoelectric EMFs, temperature drift, etc. and 50Hz interference.This design can be divided into several parts including current source,...