# US 9,038,481 B2 · Apparatus configured to detect a physical quantity of a flowing fluid, and a respective method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,038,481 B2 - Document ID: US9038481B2 - Status: Granted - Kind: B2 - Application number: 13/500,933 - Filed: 2010-10-08 - Published: 2012-10-25 - Granted: 2015-05-26 - Earliest claimed: 2009-10-08 - Assignees: Nederlandse Organisatie voor toegepast-natuurwetenschappelijk onderzoek TNO - Applicants: Wouter Schiferli - Inventors: Wouter Schiferli - Web page: https://patentgrep.com/patent/US9038481B2 ## CPC - G01F 1/3227: {using fluidic oscillators (fluidic oscillators per se F15C1/00)} - G01F 1/325: Means for detecting quantities used as proxy variables for swirl - G01N 9/002: {using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis (G01N9/34 takes precedence)} - G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract Apparatus configured detect a physical quantity, for example a density, of a flowing fluid, the apparatus including: a sensor body (2) configured to extend into the flowing fluid, the sensor body comprising a fiber Bragg grating (FBG) of a fiber Bragg grating sensor (3, 7, FBG), for generating a detector signal relating to vibration of at least part (2B) of the sensor body (2); and a processing unit, configured to process the detector signal, and to determine the physical quantity based on detected vibration at a mechanical eigenfrequency of the flexible part (2B) of the sensor body (2). ## Claims ### Claim 1 Apparatus configured to detect a physical quantity of a flowing fluid, the apparatus including: a sensor body configured to extend into the flowing fluid and comprising a fiber Bragg grating sensor, for generating optical detector signals relating to fluid induced vibrations of a flexible part of the sensor body, the fluid induced vibrations including both a vortex shedding frequency and a mechanical eigenfrequency; and a detector signal processing unit, configured to detect the optical detector signals and determine both the flow rate of the fluid from the vortex shedding frequency and the physical property of the fluid from the mechanical eigenfrequency, based on the vortex shedding frequency and the mechanical eigenfrequency of the flexible part being within a same frequency spectrum of the optical detector signals and a separation between the mechanical eigenfrequency and the vortex shedding frequency of at least 100 Hz. ### Claim 2 (depends on 1) The apparatus according to claim 1, wherein the sensor body comprises a fiber Bragg grating of the fiber Bragg grating sensor, the eigenfrequency f being an eigenfrequency of the flexible element. ### Claim 3 (depends on 1) The apparatus according to claim 1, wherein the flexible part extends in parallel with a flow path of the fluid. ### Claim 4 (depends on 1) The apparatus according to claim 1, the processing unit being configured to detect deviation of the actual eigenfrequency f of the flexible part of the sensor body from an initial eigenfrequency f0 of that part. ### Claim 5 (depends on 1) The apparatus according to claim 1, wherein the processing unit has or is associated with a memory, configured for storing an initial eigenfrequency f0. ### Claim 6 (depends on 1) The apparatus according to claim 1, wherein the eigenfrequency of the flexible sensor body part is lower than 10000 Hz. ### Claim 7 (depends on 1) The apparatus according to claim 1, the sensor body having a rigid part to connect the sensor body to a wall of a fluid channel, wherein the flexible part includes a fiber Bragg grating being connected to the rigid part, the apparatus further comprising an optical fibre that includes the fiber Bragg grating passing through the rigid part to the flexible part. ### Claim 8 (depends on 1) The apparatus according to claim 1, including or being associated with a vibration inducer, configured to induce vibration of the flexible part of the sensor body using the flowing fluid. ### Claim 9 (depends on 1) The apparatus according to claim 1, the sensor body being a vortex shedder that is configured to generate Karman vortices in the fluid during operation. ### Claim 10 (depends on 9) The apparatus according to claim 9, wherein a Karman vortex frequency (fK) of vortices generated by the vortex shedder is detectable utilizing the optical detector signals, wherein the optical detector signals include fiber Bragg grating sensor signals relating to the respective fiber Bragg grating of the vortex shedder. ### Claim 11 (depends on 10) The apparatus according to claim 10, wherein the Karman vortex frequency (fK) is lower than the natural frequency of the sensor body or the flexible part thereof. ### Claim 12 (depends on 1) The apparatus according to claim 1, wherein a thickness of the flexible sensor body part is smaller than 4 mm. ### Claim 13 (depends on 1) The apparatus according to claim 1 wherein the processing unit is configured to determine the frequency spectrum of the optical detector signal. ### Claim 14 (depends on 1) The apparatus according to claim 1 wherein the physical quantity is a density (rho) of the fluid. ### Claim 15 (depends on 6) The apparatus of claim 6, wherein the eigenfrequency of the flexible sensor body part is less than 2000 Hz. ### Claim 16 (depends on 12) The apparatus of claim 12, wherein the thickness of the flexible sensor body part is less than 2 mm. ### Claim 17 (depends on 1) The apparatus of claim 1, wherein the mechanical eigenfrequency, f, of the flexible part in the flowing fluid is defined by: f=f0·(1+K·rho)−1/2 wherein f0 is an initial eigenfrequency (Hz) of the flexible part in vacuum, rho is the density of the fluid (kg/m3) and K is a constant (m3/kg) associated with the dimensions and mass of the flexible part. ### Claim 18 Apparatus configured to detect a physical quantity of a flowing fluid, the apparatus including: a sensor body configured to extend into the flowing fluid and comprising a fiber Bragg grating sensor, for generating optical detector signals relating to vibrations of a flexible part of the sensor body, the fluid induced vibrations including both a vortex shedding frequency and an actual eigenfrequency; and a processing unit, the processing unit having or being associated with a memory, configured for storing an initial eigenfrequency f0 of the sensor body part, corresponding to a natural eigenfrequency of the sensor body part in vacuum, the processing unit being configured to utilize the optical detector signals for detecting the vortex shedding frequency and the actual eigenfrequency of the flexible part of the sensor body, for determining a deviation of the detected actual eigenfrequency of the flexible part of the sensor body from the stored initial eigenfrequency of the flexible part, wherein the apparatus is configured such that the vortex shedding frequency and the mechanical eigenfrequency are within a same frequency spectrum of the optical detector signals and a separation between the vortex shedding frequency and the mechanical eigenfrequency is at least 100 Hz. ### Claim 19 (depends on 18) Apparatus according to claim 18, wherein the processing unit is configured to determine the physical quantity based on the detected deviation. ### Claim 20 A method of detecting a physical quantity of a flowing fluid, the method comprising inducing vibrations of a flexible part of a sensor body at both a first frequency, corresponding to a vortex shedding frequency, and an eigenfrequency the method further comprising detecting optical detector signals relating to both the vortex shedding frequency and mechanical eigenfrequency, and determining both the flow rate of the fluid from the vortex shedding frequency and the physical quantity of the fluid from the mechanical eigenfrequency, wherein the mechanical eigenfrequency and the vortex shedding frequency of the flexible part are within a same frequency spectrum of the optical detector signals and a separation between the mechanical eigenfrequency and the vortex shedding frequency is at least 100 Hz. ### Claim 21 (depends on 20) The method according to claim 20, including: inducing vortices that lead to the flexible part vibrating at the vortex shedding frequency, wherein the vortex shedding frequency is lower than the eigenfrequency. ### Claim 22 (depends on 21) The method according to claim 21, wherein the vortex shedding frequency and eigenfrequency are detected using a same sensor. ### Claim 23 (depends on 20) The method according to claim 20, wherein the optical detector signals relating to the vortex shedding frequency and the eigenfrequency are detected using a fiber Bragg grating. ### Claim 24 (depends on 20) The method according to claim 20, the method including: providing a sensor body that extends into the flowing fluid, the sensor body comprising a fiber Bragg grating of a fiber Bragg grating sensor, that generates the optical detector signals relating to the vortex shedding frequency and mechanical eigenfrequency of the flexible part, wherein the mechanical eigenfrequency, f, of the flexible part in the flowing fluid is defined by: f=f0·(1+K·rho)−1/2 wherein f0 is an initial eigenfrequency (Hz) of the flexible part in vacuum, rho is the density of the fluid (kg/m3) and K is a constant (m3/kg) associated with the dimensions and mass of the flexible part. ### Claim 25 (depends on 20) The method according to claim 20, including: providing a sensor body that extends into the flowing fluid, the sensor body comprising a fiber Bragg grating of a fiber Bragg grating sensor, that generates the optical detector signals; and processing the optical detector signals for detecting the mechanical eigenfrequency of the flexible part of the sensor body; and determining a deviation of the detected eigenfrequency of the flexible part from a predetermined initial eigenfrequency of the flexible part. ### Claim 26 (depends on 25) The method according to claim 25, wherein the processing includes the use of a frequency spectrum of the optical detector signal. ### Claim 27 (depends on 26) The method of claim 26, wherein the processing includes the detection of a peak in said frequency spectrum, which peak is associated with said actual mechanical eigenfrequency. ### Claim 28 (depends on 20) The method according to claim 20, wherein the eigenfrequency is lower than 1000 Hz. ### Claim 29 (depends on 20) The method of claim 20, wherein the physical quantity is density.