Patent ID: 7466399

Claim:
An optical flow meter for measuring a flow of fluid through a pipe, the optical flow meter comprising: (a) a wave energy source for generating a pair of beams; (b) a driver for controlling the wave energy source; (c) a modulator coupled to said wave energy source for modulating a phase of one of said pair of beams at a phase modulation frequency; (d) means for directing said pair of beams in opposite directions along a path through the flow of fluid; (e) means for receiving a pair of diffused beams after said pair of beams have crossed said path; (f) a detector for detecting said pair of diffused beams and for producing an electrical signal representative of a phase difference between said pair of diffused beams; (g) a digital signal processor configured to receive said electrical signal and calculate a flow velocity from said phase difference between said pair of diffused beams; (h) a pair of collecting optical systems positioned at opposite ends of said path adjacent to said means for directing said pair of beams for collecting deflected wave energy from said pair of beams; and (i) a compensation module coupled to receive said deflected wave energy from said collecting optical systems, said compensation module configured to estimate a total intensity of wave energy received by said means for receiving said pair of diffused beams and to generate a compensation signal representative of said total intensity of wave energy received, and coupled to provide said compensation signal to said driver, whereby said driver controls said wave energy source to vary an initial intensity of said pair of beams in response to said compensation signal such that said total intensity of wave energy received remains constant.