Fluid flow velocity meter - uses microprocessor in phase locked loop circuit including oscillator and transducers

摘要

The velocity meter is able to measure the speed of fluid flow by propagation of an acoustic wave in the fluid. The difference in frequency between this signal and a direct signal is measured and corrections automatically applied to obtain the flow speed. Two transducers (1, 2) are alternately switched (3) to act as emitters or receivers. Correlation between transmitted and received signals (5, 6) is determined by a multiplier circuit (4) whose output is applied via an amplifier (12) the gain of which is controlled by a microprocessor (13). This signal is passed via a a filter (14) to a VCO (15) having its output divided down (17) and amplifier (19) to drive the transducers. The microprocessor senses the oscillator frequency and an output signal ensures that a phase locked loop is obtained.