The High Precision And Fast Measurement Method Of Sound Travel-time Based On The Cross-correlation

In recent years, people found that the relationship between the temperature field monitoring and quantitative measurement of human production or life become more and more close. It has a very important practical significance. Therefore, a new temperature field measurement methods and technologies are emerging, and acoustic measurement is one of them. Due to acoustic measurement with high accuracy, wide measurement range, measurement space, non-contact, continuous real-time, easy maintenance and other significant advantages, is regarded as the most promising method of temperature measurement and technology. However, in order to meet the real-time, on-line and accurate temperature measurement requirements, it must achieve high precision and fast measurement of Sound travel-time in acoustic temperature measurement technique. It directly determines the quality and success of the temperature field measurement(reconstruction). Therefore, in this paper, under laboratory conditions and in air medium, take the cross correlation algorithm and pseudo random sequence coding method to achieve the expected targets on high precision and fast measurement of Sound travel-time.The principle of this method is, First, use the pseudo-random sequence coded modulation technique on acoustic emission signal, so that the sound can be cross-correlation between transmit and receive signals; Second, calculate the cross-correlation peak search of the acoustic emission and reception signals. Then the peak point is the time delay which disseminates between the transmit and receive sensor, namely for travel time on the sound propagation paths; Therefore, has succeeded in developing a measurement system of Sound travel-time: Uses 40 kHz as carrier signal frequency, uses m sequence as pseudo-random coded modulation sequence which produced by six shift register, and use 100 kHz as the sampling rate of the signal.Under laboratory conditions and in air medium, measure the travel-time by the Sound travel-time measurement system: in two cases, whether there is interference signal or not, sound waves at different distances(the same medium temperature) and different media temperature(the same distance). Through the analysis of the measurement data, we know that: First, regardless of whether there is noise signal interference, at the same medium temperature, with the increase of the propagation distances, absolute measurement error increases, the relative error decreases. However, when the distance is constant, along with the temperature increase, the survey absolute error and the relative error all increases. Second, when non-noise signal disturbance, the sound wave transit time measuring accuracy satisfies the predetermined target(<10μs); When there exists noise interference, the sound measurement of Sound travel-time is larger than non-noise signal condition, but also basically satisfies the predetermined target. At the same time, the single-channel travel time can satisfies the predetermined target(<20ms); Third, the measurement accuracy of ―Cross-correlation with pseudo random sequence method‖ is five times higher than ―Burst normalized threshold point method‖. Compared with other traditional methods, ―Cross-correlation with pseudo random sequence method‖ has the remarkable superiority in the measurement of Sound travel-time.