The Research On Ultrasonic Technique For Non-intrusive Pressure Testing In Pipes

Pressure measurement is the main option for status observation and fault-diagnosis of piping system. Conventional methods, such as testing by the strain sensor and by the mechanical pressure gauge, are testing in the invasive way. The disadvantage is that any one of those methods have to measure the pressure in a fixed location and with low reliability. Sometimes, those fixed locations may destroy the structure of the pipeline and bring many safety threats especially under high pressure. Consequently, the research on non-intrusive pressure testing theory and the testing device has great practical significance and application prospect.This dissertation has approached the theory on the non-intrusive measurement and presented a way to test the pressure by the ultrasound. For the pressure exerts an influence on the ultrasound propagation parameters (such as acoustic attenuation coefficient and velocity, etc.) and the acoustic attenuation coefficient is also related to other reasons, it is better to test the pressure by the ultrasonic velocity. Specifically, in a fixed conveying distance, the time delay of the ultrasound is measured instead of the ultrasonic velocity. In addition, temperature also plays a great role in ultrasound, so temperature should be measured accurately while testing.At present, the non-invasive measurement based upon ultrasound is still in its infancy, and there are no reliable solution and flexible products in China. In this dissertation, firstly the theory about testing pressure by using ultrasonic method is presented and the expression of the ultrasound wave under the influence of the velocity is built up. Secondly, the design and debug of the hardware circuits, which include the ultrasonic emitting circuit, signal processing circuit, A/D converting circuit, time control circuit based on CPLD and so on, are illustrated in details. Thirdly, as for the noise disturbing, it's necessary to process the pulse-echo signal by using DSP (Digital Signal Processing) technology to get the exact time delay parameter. To solve this problem, a new DSP method, which is called sparse decomposition, is presented and analyzed. The sparse decomposition technology is based on the signal's characteristics, choosing the basic elements from the over-complete dictionary to rebuilt the signal, and get the most effective decomposition of the signal. Compared with other traditional methods (such as timing counter and magnitude-magnitude method), the research results show that this signal decomposition method can calculate the time delay of pulse-echo signal accurately, correspondently, the precision of the hydraulic testing has been improved. Finally, the artificial neural networks are used to build up the system model of ultrasonic velocity and hydraulic pressure.In a word, the study shows that this pressure testing method by using ultrasonic technique is feasible. And there is a certain relationship between the pressure and ultrasonic velocity. This dissertation can provide some references for further research.