| The operation of an oil well requires the measurement of temperature, pressure and the fluid level. Those parameters are used to monitor and control the operation of the oil well. And the fluid level is a very important parameter.Most present acoustic level gauges use a sound generator which can produce high-power acoustic waves and a microphone which can detect the echo signal. The fluid level can be worked out based on the artificial analysis of the echo curve. In this way, the influence of artificial disturbing in the measurement is unavoidable and the result is not very accurate and can not be measured automatically and directly, furthermore, there are some unsafe elements for the use of gun powder which is used to generate a high-power acoustic signal. Searching a new method to measure the fluid level accurately, safely and directly becomes important. A new fluid level measurement method, based on ultrasonic measurement, for calculating the velocity of sound and the fluid level is presented. This method points out that a low-power acoustic signal generator under control can be used to emit spread spectrum signals and the fluid level can be worked out by detecting the correlation-peak output of the matching filter whose input is the echo signal received by a microphone. The method, utilizing computer technique, removes the influence of artificial reading & calculating, makes the measurement accurate, easy, direct and safe.This thesis firstly introduces the method of ultrasonic measurement and analyzes the properties of the acoustic channel. In the second part,the new method is compared with the old one in such aspects as system structure and signal processing methods. In the third part, the properties of DSSS and LFM systems, especially the echo signal correlation processing of the systems are discussed. The last part are the respective analyses of water-pipe simulation experiment results and the trial results in Zhong Yuan oil field. |
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