Patent ID: 7775125
Filing Date: 2010-08-17
Classification: G01F

Abstract:
1. A method of ultrasonic flow measurement for measuring a flow rate of a fluid in a conduit, the method comprising the steps of: (a) providing an ultrasonic flow meter comprising a microprocessor, a clock, a fast clock, and a pair of ultrasonic transducers operable to transmit ultrasonic signals through the fluid at an angle other than 90 degrees to a predominant direction of flow and to receive the transmitted signals; (b) switching the ultrasonic flow meter from a passive state to an active state at time intervals measured by the clock, an amount of power used by the ultrasonic flow meter in the passive state being less than an amount of power used by the ultrasonic flow meter in the active state; (c) transmitting and receiving at least one ultrasonic signal in the active state, the ultrasonic signal having an associated transit time to travel from one ultrasonic transducer to the other; (d) measuring the transit time of the ultrasonic signal with a counter clocked by the fast clock; (e) comparing the phases of the transmitted and received signals; (f) providing a pulsing signal having a pulse width which varies in dependence upon a result of the phase comparison step; (g) charging a capacitor using the pulsing signal; (h) measuring a voltage on the capacitor; (i) calculating the flow rate based at least partially upon the measured transit time and at least partially on the measured voltage; and (j) switching the ultrasonic flow meter from the active state to the passive state following the calculation of the flow rate.