# US 5,708,495 A · Method and apparatus for determining the velocity of a gas flow > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,708,495 A - Document ID: US5708495A - Status: Granted - Kind: A - Application number: 08/522,943 - Filed: 1995-09-01 - Granted: 1998-01-13 - Earliest claimed: 1995-09-01 - Assignees: Vanderbilt University - Inventors: Robert W. Pitz; Peter A. DeBarber; Thomas M. Brown, III - Web page: https://patentgrep.com/patent/US5708495A ## CPC - G01P 5/18: by measuring the time taken to traverse a fixed distance - G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G}) ## Abstract A method and apparatus for measuring the velocity of a gas flow that does not require the seeding of the flow is disclosed. The method and apparatus produce a population of stable molecules within the flow. This population of stable molecules is produced within the flow at a first time point. A population of excited molecules is produced from the stable molecules at a second time point by exciting the stable molecules with a laser beam. This laser beam also induces fluorescence in the population of excited chemical species at the second time point. Typically, the interval between the first and second time points is known and the velocity of the flow is calculated by dividing the distance travelled by the stable molecules in the flow by the known time interval. The preferred example of the stable molecule is ozone. Oxygen molecules are fluoresced by a 193 nm laser beam at a first time point, producing oxygen atoms. Ozone is also generated in the flow with a 193 nanometer laser beam through the reaction of these oxygen atoms and molecules at the first time point. A population of excited oxygen molecules can be produced from the ozone and can be subsequently fluoresced by a 248 nanometer laser at a second time point. The velocity of the flow is determined by measuring the distance between the first and second fluorescence events and dividing this distance by the known time interval between the two time points. Since ozone is formed rapidly within the flow and is stable, both high and low speed flows can be measured using the method and apparatus of this invention. ## Claims ### Claim 1 A method of measuring velocity of a gas flow, the method comprising the steps of: a. producing a population of stable molecules within the flow at a first location at a first time point; b. producing a population of excited chemical species within the flow by exciting the stable molecules; c. inducing fluorescence in the population of excited chemical species at a second time point; d. detecting a fluorescence event of the population of excited chemical species at a second location at the second time point; and e. calculating the velocity of the gas flow by dividing a distance between the first and second locations by an amount of time elapsed between the first and second time points. ### Claim 2 (depends on 1) The method according to claim 1 wherein the step of producing a population of excited chemical species within the flow by exciting the stable molecules is performed with a first laser beam and the step of inducing fluorescence in the population of excited chemical species at the second time point is performed with a second laser beam. ### Claim 3 (depends on 1) The method according to claim 1 wherein the steps of producing a population of excited chemical species within the flow by exciting the stable molecules and inducing fluorescence in the population of excited chemical species are performed with a single laser beam. ### Claim 4 (depends on 1) The method according to claim 1 wherein the second time point occurs at a known time interval from the first time point. ### Claim 5 (depends on 1) The method according to claim 1 further comprising the steps of repeating steps (b) and (c); detecting an additional fluorescence event of the population of excited chemical species at a third location within the flow at a third time point; and calculating the velocity of the gas flow by dividing a distance between the second and third locations by an amount of time elapsed between the second and third time points. ### Claim 6 (depends on 1) The method according to claim 1 wherein the stable molecule is ozone. ### Claim 7 (depends on 4) The method according to claim 4 further comprising repeating steps (a) through (d) of the method to generate multiple distance measurements; averaging the multiple distance measurements; and calculating the velocity of the gas flow by dividing the average distance by the known time interval. ### Claim 8 (depends on 6) The method according to claim 6 wherein the population of excited chemical species comprises oxygen molecules. ### Claim 9 (depends on 6) The method according to claim 6 wherein the population of excited chemical species comprises oxygen atoms. ### Claim 10 A method of measuring velocity of a gas flow, the method comprising the steps of: a. exciting a first population of chemical species within the flow with a first laser beam to induce fluorescence and to produce a first population of excited chemical species and producing stable intermediate molecules from the first population of excited chemical species with the first laser beam; b. obtaining a location of the first population of excited chemical species by detecting the fluorescence of the first population of excited chemical species at a first time point; c. producing a second population of excited chemical species by exciting the stable intermediate molecules with a second laser beam at a second time point; d. inducing fluorescence in the second population of excited chemical species with the second laser beam at the second time point; e. obtaining a location of the second population of excited chemical species by detecting the fluorescence of the second population of excited chemical species at the second time point, f. determining a distance between the location of the first population of excited molecules and the location of the second population of excited molecules and determining an amount of time elapsed between the first and second time points; and g. calculating the velocity of the gas flow by dividing the distance between the location of the first population of excited molecules and the location of the second population of excited molecules by the amount of time elapsed between the first and second time points. ### Claim 11 (depends on 10) The method according to claim 10 wherein the second time point occurs at a known time interval from the first time point. ### Claim 12 (depends on 11) The method according to claim 11 further comprising repeating steps (a) through (f) of the method to generate multiple distance measurements; averaging the multiple distance measurements; and calculating the velocity of the gas flow by dividing the average distance by the known time interval. ### Claim 13 (depends on 11) The method according to claim 11 wherein the first and second time points are established by firing the first and second laser beams into the flow on a cycle based on the known time interval. ### Claim 14 (depends on 11) The method according to claim 11 wherein the known time interval is a fixed interval. ### Claim 15 (depends on 10) The method according to claim 10 wherein the stable intermediate molecule is ozone. ### Claim 16 (depends on 15) The method according to claim 15 wherein the population of excited chemical species comprises oxygen molecules. ### Claim 17 (depends on 15) The method according to claim 15 wherein the population of excited chemical species comprising oxygen atoms. ### Claim 18 (depends on 15) The method according to claim 15 wherein the first laser beam has a wavelength of about 193 nm. ### Claim 19 (depends on 15) The method according to claim 15 wherein the second laser beam has a wavelength of about 248 nm. ### Claim 20 (depends on 15) The method according to claim 15 wherein the second laser beam has a wavelength of about 226 nm. ### Claim 21 A method for determining the velocity of an gas flow comprising the steps of: a. exciting a first population of oxygen chemical species within the flow with a first laser beam to induce fluorescence and to produce a first population of excited oxygen chemical species; b. obtaining a location of the first population of excited oxygen chemical species within the flow by detecting the fluorescence of the first population of excited oxygen chemical species at a first time point; c. producing ozone molecules from the first population of excited oxygen chemical species; d. producing a second population of excited oxygen chemical species by exciting the ozone molecules with a second laser beam at a second time point; e. inducing fluorescence in the second population of excited oxygen chemical species with the second laser beam at the second time point; f. obtaining a location of the second population of excited oxygen chemical species within the flow by detecting the fluorescence of the second population of excited oxygen chemical species at the second time point; and g. calculating the velocity of the gas flow by dividing a distance between the location of the first population of excited oxygen chemical species and the location of the second population of excited oxygen chemical species by an amount of time elapsed between the first and second time points. ### Claim 22 (depends on 21) The method according to claim 21 wherein the second population of excited oxygen chemical species comprises oxygen molecules. ### Claim 23 (depends on 21) The method according to claim 21 wherein the second population of excited oxygen chemical species comprises oxygen atoms. ### Claim 24 (depends on 21) The method according to claim 21 wherein the first laser beam has a wavelength of about 193 nm. ### Claim 25 (depends on 21) The method according to claim 21 wherein the second laser beam has a wavelength of about 248 nm. ### Claim 26 (depends on 21) The method according to claim 21 wherein the second laser beam has a wavelength of about 226 nm. ### Claim 27 (depends on 21) The method according to claim 21 wherein the second time point occurs at a known time interval from the first time point. ### Claim 28 (depends on 27) The method according to claim 27 further comprising repeating steps (a) through (f) of the method to generate multiple distance measurements; averaging the multiple distance measurements; and calculating the velocity of the gas flow by dividing the average distance by the known time interval. ### Claim 29 (depends on 27) The method according to claim 27 wherein the first and second time points are established by firing the first and second laser beams into the flow on a cycle based on the known time interval. ### Claim 30 (depends on 27) The method according to claim 27 wherein the known time interval is a fixed interval. ### Claim 31 Apparatus for measuring velocity of a gas flow, the apparatus comprising: a. means for producing a population of stable molecules at a first location within the flow at a first time point; b. means for producing a population of excited chemical species in the flow by exciting the stable molecules; c. means for inducing fluorescence in the population of excited chemical species at a second location at a second time point; d. means for detecting a fluorescence event of the population of excited chemical species at the second location at the second time point. ### Claim 32 (depends on 31) The apparatus according to claim 31 further comprising means for calculating the velocity of the gas flow by dividing the distance between the first and second locations by an amount of time elapsed between the first and second time points. ### Claim 33 (depends on 31) The apparatus according to claim 31 wherein the means for producing a population of stable molecules within the flow comprise a laser beam generating means, means for producing an electrical arc, an ultraviolet lamp, or an ozone generator. ### Claim 34 (depends on 31) The apparatus according to claim 31 wherein the means for producing a population of excited chemical species in the flow by exciting the stable molecules and the means for inducing fluorescence in the population of excited chemical species at a second time point comprise the same means. ### Claim 35 (depends on 31) The apparatus according to claim 31 wherein the means for producing a population of excited chemical species in the flow by exciting the stable molecules comprise laser beam generating means. ### Claim 36 (depends on 31) The apparatus according to claim 31 wherein the means for inducing fluorescence in the population of excited chemical species at a second time point comprise laser beam generating means. ### Claim 37 (depends on 31) The apparatus according to claim 31 further including means for establishing the amount of time elapsed between the first and second time points as a fixed interval. ### Claim 38 (depends on 34) The apparatus according to claim 34 wherein the means for producing a population of excited chemical species in the flow by exciting the stable molecules and the means for inducing fluorescence in the population of excited chemical species at a second time point comprise laser beam generating means. ### Claim 39 (depends on 38) The apparatus according to claim 38 wherein the laser beam generated by the laser beam generating means has a wavelength of about 248 nm. ### Claim 40 Apparatus for measuring velocity of a gas flow, the apparatus comprising: a. means for producing a first laser beam of a first wavelength at a first location within the flow, the first laser beam exciting a first population of chemical species within the flow, inducing fluorescence in the first population of excited chemical species, and producing stable intermediate molecules from the first population of excited chemical species; b. means for producing a second laser beam of a second wavelength at a second location within the flow at a second time point, the second location lying downstream in the flow from the first location, the second laser beam producing a second population of excited chemical species by exciting the stable intermediate molecules at the second time point, inducing fluorescence in the second population of excited chemical species at the second location at the second time point; and c. means for detecting fluorescence of the first and second populations of excited chemical species at the first and second locations at the first and second time points, the detecting means oriented relative to the flow such that the detecting means observes the intersection of the first laser beam with the flow and intersection of the second laser beam with the flow. ### Claim 41 (depends on 40) The apparatus according to claim 40 further comprising means for calculating the velocity of the gas flow by dividing the distance travelled between the first and second time points by an amount of time elapsed between the first and second time points. ### Claim 42 (depends on 40) The apparatus according to claim 40 further comprising means for establishing the first and second time points by firing the first and second laser beams into the flow on a cycle based on a known time interval. ### Claim 43 (depends on 42) The apparatus according to claim 42 further including means for establishing the known time interval as a fixed interval. ### Claim 44 (depends on 40) The apparatus according to claim 40 wherein the first laser beam has a wavelength of about 193 nm. ### Claim 45 (depends on 40) The apparatus according to claim 40 wherein the second laser beam has a wavelength of about 248 nm. ### Claim 46 A method of measuring velocity of a gas flow, the method comprising the steps of: a. producing a population of stable molecules within the flow at a first location at a first time point; b. inducing fluorescence in the population of stable molecules at a second time point; c. detecting a fluorescence event of the population of stable molecules at a second location at the second time point; and d. calculating the velocity of the gas flow by dividing a distance between the first and second locations by an amount of time elapsed between the first and second time points. ### Claim 47 A method of measuring velocity of a gas flow, the method comprising the steps of: a. producing a population of stable molecules within the flow at a first location at a first time point; b. inducing fluorescence in the population of stable molecules at a second time point; c. detecting a fluorescence event of the population of stable molecules at a second location at the second time point; d. determining a distance between the first location and the second location and determining an amount of time elapsed between the first and second time points; and e. calculating the velocity of the gas flow by dividing a distance between the first and second locations by an amount of time elapsed between the first and second time points.