Abstract: The virtual instrument system is the developing field of signal detecting in industry production now. It’s effective to attach the traditional electronic detecting technology to computer close and more simple and visual to process and detect the signal. The virtual instrument system is introduced that is completed by VC++6.0 based on Windows9.x, industry-control computer and PLC1800 data-acquisition-card. It can visually display the data acquisition and analysis in the screen by the three dimension interface. On the electrical signal of CO2 welding, the virtual instrument system extracted the characteristic information of welding process stability with the probability density distribution(PDD) of current and voltage and U－I chart. It was also used on the experiments of the spot welding. Experiments results indicate that the system has perfect function, strong analysis capability and steady performance .

Key words: Probability density distribution, U－I chart, Virtual analyzing instrument, Welding dynamic process