US 6,611,319 B2 · Optical flow sensor using a fast correlation algorithm

Abstract

An optical flow sensor determines the velocity of a moving flow of air or other gas utilizing a plurality of photodetectors spaced apart in a direction parallel to the direction of gas flow. An optical beam is transmitted to the photodetectors across the flowing gas. Scintillations that occur in the flowing gas due to eddies and particulates in the gas are detected in the photodetectors at slightly different times. The output signals of the photodetectors are conditioned, amplified and transformed to digital form. Temporal cross correlation analysis is then performed on the digitized signals in a digital signal processor utilizing a fast correlation algorithm in which the total number of calculations is proportional to 2N, as contrasted with conventional systems in which the number of correlations is proportional to N2. A time differential between signals from the different photodetectors is then calculated electronically. The velocity of gas flow is then determined by dividing the spatial distance of separation between adjacent photodetectors by the time difference at which the same scintillation event is detected by each photodetector.

Claims17

Dependent claims

An optical flow sensor for measuring gas flow velocity in a predetermined direction of gas flow comprising:

an optical transmitter that generates a collimated optical beam across said gas flow;
an optical receiver including a plurality of receiving lenses all located in optical communication with said optical transmitter and in the path of said optical beam and separated from each other in a direction parallel to said predetermined direction of gas flow, a separate optical photodetector for each of said receiving lenses that produces an electronic output that varies in response to scintillations occurring in said optical beam,
a separate signal-controlled gain amplifier circuit coupled to each of said optical photodetectors;
a separate analog-to-digital converter coupled to each of said gain amplifier circuits for separately digitizing outputs from each of said gain amplifier circuits;
and
a digital signal processor coupled to receive inputs from all of said gain amplifier circuits to determine the temporal cross correlation of said digitized outputs for scintillation events detected separately by all of said photodetectors using a logarithmic time delay function based upon an original data string with N=2n data points by averaging successive data points in pairs to form a new data string having a length half that of said original data string and averaging each two adjacent points of said new data string to form another data string having a length half that of said new data string and iteratively averaging adjacent data points n=log2N times to provide therefrom a path integrated flow rate in said predetermined direction of gas flow.

3 more elements

An optical flow sensor for measuring velocity of gas flow in a predetermined gas flow direction comprising:

a transmitter that includes an optical source and beam-forming optics for producing a collimated beam across said gas flow,
a receiver located in a line-of-sight path with said optical beam and including a plural number of focusing receiving lenses spaced apart from each other in a direction parallel to said predetermined gas flow direction, and a separate photodetector for each of said receiving lenses which produce electronic outputs that vary with scintillation events occurring in said line-of-sight path,
separate signal-controlled gain amplifiers for each of said photodetectors,
separate analog-to-digital converters coupled to each of said gain amplifiers for converting said outputs therefrom from analog to digital signals, and
a digital signal processor for cross correlating said digitized signals from said photodetectors as a function of time delay between the detection of scintillation events based upon a number of time delays=N using a fast correlation algorithm in which the total number of calculations of cross correlation data points is proportional to 2N to produce a signal indicative of velocity of gas flow in said predetermined gas flow direction.

2 more elements

A method of measuring velocity of gas flow in a predetermined linear direction comprising:

transmitting a collimated optical beam across a volume of gas along an optical line-of-sight path intersecting said predetermined linear direction of gas flow and crossing said gas flow,
receiving said transmitted optical beam with a plurality of receiving scintillation detectors spatially separated from each other in a direction parallel to said predetermined linear direction,
generating separate output signals from each of said receiving scintillation detectors in response to scintillations occurring in said gas flow,
separately amplifying and digitizing each of said output signals,
determining the temporal cross correlation of said separate output signals by using a logarithmic time delay function based upon an original data string with N=2n data points by averaging successive data points in pairs to form a new data string having a length half that of said original data string and averaging each two adjacent points of said new data string to form another data string having a length half that of said new data string, and iteratively averaging adjacent data points n=log2N times, and
providing a velocity output signal indicative of velocity of gas flow in said predetermined linear direction based upon distance of separation of said receiving scintillation detectors from each other and upon said temporal cross correlation of said separate output signals.

3 more elements

Dependencies are inferred from the claim text.

Optical flow sensor using a fast correlation algorithm

Life of this patent

Optical flow sensor using a fast correlation algorithm

Life of this patent

Abstract

Claims17