Research On A Novel Method For Noninvasively Measuring Pressure Based On The Ultrasonic

Pressure is one of the most important parameters in modern industry. In order to ensure the devices working properly and safely, it is necessary to monitor and control the pressure. Conventional methods, most of them belonging to the invasive method, to measure the pressure require drilling a hole in the wall of the devices, which not only induces local stress concentration, but also brings many safety problems. In this paper, a novel method to measure the pressure noninvasively based on the ultrasonic is presented. With this method, the pressure can be gotten by measuring the transit time difference of ultrasonic under different pressures. The main research achievement is showed as follows:1. Based on the model of Rayleigh waves measuring stress and thin film theory of vessels, with the surface stress as middle variable, the relationship between the velocity changes and the pressure is established for the low and middle pressure vessels or pipes. Considering velocity could not be measured directly, the relationship between the transit time difference and the pressure is deduced farther, and the effect of strain to the measurement results is also modified.2. Because the Rayleigh waves sampled by the AD card always contain the correlative colored noise, the general correlative time estimation method based on the CWT is presented to calculate the transit time difference under different pressures. According to this method, the experimental system was built. The studies were done when the Rayleigh wave propagated in the direction of axis and circumference of the vessels. The experimental results show that the proposed model could predict the relationship between the transit time difference and the pressure accurately, and the method to measure pressure using Rayleigh wave is feasible.3. To solve the problems existing in the experiment, such as low precision of time measurement, long time needed to calculate the transit time difference and high cost of the experimental devices, a new method was presented, using the electrical signal from the receiver to retrigger the transmitter, and the device was made. With this device, the precision of time measurement was improved, but the cost of experimental devices was reduced.4. The affect of temperature was discussed according to some phenomena in the experiment. Only considering the main aspects of the temperature affecting the results, the model of the transit time difference and pressure was modified, and according to this new model, a method was presented to correct the errors caused by the temperature fluctuation. The experimental results show that this method can eliminate or weaken the affect of temperature effectively.