The Research Of Correlation Method Of Ultrasonic Level Meter Based On DSP

In industry, liquid level measurement is widely used in industrial control,hydroelectric power fields. Some of the liquid level measurement environments are notsuitable to measure directly by people because of the bad environment. Level meter can beused in this kind of circumstance. Ultrasonic level meter is one kind of the non-contactlevel meters, it is widely used since the advantages of high precision, easy installation andmaintenance, wide applicable scope and cheap, which can improve the intelligence andsecurity of the industrial production.The basic measuring principle of ultrasonic level meter is to calculate the liquid levelinformation through measuring the delay time from transmitting to receiving and theultrasonic velocity in the air. The threshold value comparison method is generally used inthe measurement of delay time, in view of the threshold method is easy to turn error withthe interference, the measurement error is large, so cross-correlation algorithm is used tocalculate the delay time in this paper.In order to improve the real-time processing ability of ultrasonic level meter, DSPdigital signal processor is used in this paper as the master control chip，its type isTMS320C5402. Ultrasonic launch sensor launches the ultrasonic signal with the powerdrive circuit by the square wave signal of40kHz launched by the DSP, the ultrasonic signalwill be reflected by the level surface when it is spreading in the air, ultrasonic receive senorreceives the reflected ultrasonic signal, then through the A/D sampling after dealing withthe amplification, filter and automatic gain circuit, and then the sampling signal is sent toDSP for the data processing with the cross-correlation algorithm to calculate the levelinformation. Because of the ultrasonic transmitted signal is short and the ultrasonicreceived signal is long, overlap retaining method is used in this paper which makes thelong received sequence into sections. It can improve the efficiency of the program andensure the real-time of the system by using the real sequence fast Fourier transformalgorithm. Through the error analysis of the ultrasonic level meter, we can see that thestrong anti-interference ability of the cross-correlation algorithm, the measured results are almost not affected by the noise and the accuracy of the ultrasonic level meter is improved.