| 摘要 |
<p>A method for measuring a flow velocity of a liquid uses a signal transmitter and receiver. First a region of the liquid where flow velocity is to be determined is selected at a chosen distance from the transmitter. A time period for a for a signal to travel from the transmitter to the receiver via the region is calculated and a plurality of pulsed stochastic noise signals are sequentially transmitted to said region at a given pulse repetition frequency. The reflected signals are received when said time period for each transmitted pulse has elapsed and they are correlated with a copy of the corresponding transmitted signals to identify the reflected signals. A Doppler shift signal whose frequency is representative of the frequency differences between the transmitted and received signals is generated. The Doppler shift signal is sampled at two rates below the Nyquist limit to provide perceived frequency values which are then de-aliased to give a true frequency reading before the flow velocity is then calculated. <IMAGE></p> |
