Weak DC Voltage Signal Etection

There are many methods to detect weak DC voltage signal. The moststraightforward method is amplifying the signal using the amplifier, and then using thestandard voltmeter to detect. The DC signal detection is easily affected by the insidesystem noise and the external noise of the system. In amplifying weak DC voltagesignal process, the signal can not avoided being attached by some certain detectionerror, especially maladjustment error caused by the amplifier circuit. In addition, thedrift of the amplifier output is often very serious, and vulnerable to be impacted byexternal conditions. Based on the above background, the detection scheme is using themodulator making weak DC signals into an AC signal. Amplifying the AC signal iseasier to implement than the DC signal amplification, but also have small influence ofthe offset error from the amplifying circuit. The amplified AC signal can be detectedusing the sophisticated digital algorithm, and through the amplitude demodulationconversioning result. This can complete the weak DC signal measurement.In this thesis, some weak DC signal detection issues are discussed. The main taskof the study includes the following aspects: analyzing the characteristics of the randomsignal; analyzing the sources and the characteristics of the circuit system noise; DCmodulation circuit system researching and designing; making an in-depth study tolock-in amplifier, and making a thorough research to the digitization and digitalphase-sensitive detection algorithm base on the basis of the lock amplifier; analyzingdata acquisition based on LabVIEW and data acquisition card MPS-150102; discussingdigital signal lock algorithm.This thesis completes the front-end DC modulation circuit and amplifier circuit,also completes the back-end data acquisition and digital detection processing of signal.First, through system testing results that the front-end circuit can realize the conversionfrom DC signal to200Hz square-wave AC signal. The square-wave signal can beamplified by amplifying circuit, then we use the MPS-150102acquiring the signal inreal time, and sent signal sequences to the LabVIEW platform, and achieve digitalphase sensitive detection, and finally display the weak DC signal amplitude information through a virtual instrument on computer. The test results show thatsystem can achieve the detection of weak DC voltage signal.