Performance Improvement of Ultrasonic Doppler Flowmeter Using Spread Spectrum Technique

A new method of ultrasonic flow rate measurement is presented. The range resolution of flow rate measurement is provided without velocity limitation and the same frequency interference also can be reduced greatly. In this method a pseudo random code is applied to modulate transmitting signal, the spectrum is spread widely. Receiving signal of interest region can be recovered by demodulation, because of the pseudo random code has characteristics of sharp autocorrelation. Thus the function of range resolution is realized. At the same time the same frequency interference spectrum is still spread widely, so the interference is reduced after passing a band-pass filter. The principle of the system is introduced in details. The realization of measuring system and the results of experiment are presented too.