Research And Implementation Of Low-frequency Virtual Oscillograph Based On LabVIEW

Virtual Instruments is a kind of instruments which is composed of personal computer, instrument hardware and application software. It works through the hardware to acquisit external signal, and software programming to measure, display and so on. This paper is about the research and implementation of a low-frequency virtual oscillograph which is based on the theory of virtual instrument and data acquisition.The main research content, work and production of this thesis are as follows:1. The background and significance of the research of virtual oscillograph was illustrated, its current research state and the development trend were analyzed and synthesized. The drawbacks of the traditional oscillograph were summarized: fixed-function, low-speed and high cost etc. Based on the questions above, the objectives and content of research were set.2. The relevant theories of virtual instruments and data acquisition were introduced to provide basis theories and methods of the development of a low-frequency virtual oscilloscope. The concept, structure and characteristics of virtual instruments were given, and the theorem of sample, the methods of quantization and coding were described. Then the LabVIEW development platform was introduced, and its features, applications and methods of programming were described in detail.3. According to the goal of design, firstly, the overall design of the system was given. Secondly, the design methods of hardware were described in detail, the principles and circuit interfaces of multi-channel selection, programmable gain amplifier, S/H, A/D, micro-control and USB communication were given. Last, the reliability and anti-interference technologies used in the hardware and software design were described.4. The method of design the low-frequency virtual oscillograph software system was described in detail. First of all, the overall design of the software was put forward and the application programs of MCU and PC were compiled by C and LabVIEW. With an algorithm gain reduction, a method based on calling dynamic link library was adopted to achieve USB communication, and the relevant program flow charts were given.5. A prototype was developed successfully. The process of the test was described in detail with some examples were used to verify the system. The result of the test proves that the low-frequency virtual oscillograph is operating well, meeting the system requirements.