A DAQ card based mixed signal virtual oscilloscope

摘要

Complex signals find many applications in SONAR, RADAR, Echo Location Systems and for studying the resonant frequencies. Digital Storage Oscilloscopes (DSO) is used these days for acquisition and display of routine signals. This instrument, found in every measurement laboratory, though potent in displaying simple periodic waveforms like sinusoids fails when frequency-varying time signals are applied. This problem surfaces because the underlying technique of oscilloscope used to trigger the waveform does not acquiesce with complex signals like chirp. Ready solution to this problem is the mixed signal oscilloscope. This is a costly solution and small laboratories cannot afford to have the costly instruments. In this paper, a cost effective DAQ card based mixed signal virtual oscilloscope is proposed to study the complex signals. An intelligent technique, Weighted Hamming Distance (WHD) algorithm was used to accurately trigger the complex waveforms. Also for frequency domain analysis, Joint Time Frequency Analysis (JTFA) techniques were used. A LabVIEWTM based virtual instrument was designed and developed with a capability to acquire, display and analyze the triggered signal. The integrated programming language LabVIEWTM was chosen as it offers many simple ready to use functions. In a way the proposal offers a cost effective, fast and flexible solution to treat the complex signals. The need to create such solutions is the consequence of costly hardware systems. The deficiency of conventional hardware, scheme for the virtual oscilloscope for complex signals with some real time experimental results are presented in this work.