Arrangement and method for disturbance correction for imaging flow measuring processes

Patent metadata

Field	Value
Publication number	US-10921585-B2
Application number	US-201816628391-A
Country	US
Kind code	B2
Filing date	Jul 10, 2018
Priority date	Jul 11, 2017
Publication date	Feb 16, 2021
Grant date	Feb 16, 2021

Abstract

A generally time-varying boundary surface between a plurality of flowing fluids having different refractive indices, e.g. the boundary surface between water and air with an open water surface, produces an optical disturbance. Optical flow measurement procedures that occur through the boundary surface are affected by this disturbance, which can lead to significant measurement deviations or can even completely prevent a measurement from being made.
The invention contributes to solving this metrological problem by proposing arrangements and methods for instantaneous, hardware-based correction of optical disturbances caused by a fluctuating boundary surface. For this purpose, a wavefront modulator is introduced into the beam path of the optical measuring method, the modulator actively compensating for the optical disturbance by means of a control system.
The invention makes it possible to perform optical flow measurements through a fluctuating boundary surface. It is not limited to a single flow measurement technique, but can be implemented in all known imaging methods.
The invention can be used in a variety of technical applications. Some examples include: liquid-air boundary surfaces, e.g. in water channels with an open surface; film streams, e.g. in process techniques for cooling, purification or distillation; jets of fluid with surfaces fluctuating on all sides; measurements in levitated drops or drops adhering to an opaque base, or gas bubbles occurring in liquids. The invention is also suitable for the correction of disturbances caused by temperature gradients in combustion, pressure gradients, such as in pressure surges, or concentration gradients, such as in electrolysis processes.

First claim

The invention claimed is:

1. An arrangement for correcting optical disturbances caused by a boundary surface in imaging flow measuring methods for measuring a flowing fluid, wherein the flowing fluid contains tracers which are formed as scattering particles,
said arrangement comprising:
an illumination source designed to illuminate a measuring field through which the flowing fluid flows, wherein a stationary optical pattern is disposed in the measuring field;
at least one camera adapted to record the flow pattern as an image of the light scattered by the tracers in the flowing fluid and to record the pattern image as an image of the light scattered by the stationary pattern,
wherein the illumination source and/or the at least one camera are arranged so that the illumination and/or the observation of the flowing fluid and the pattern is done through the boundary surface;

a controllable wavefront modulator is disposed in the optical path between the measuring field and the camera or in the optical path between the illumination source and the measuring field or in the optical path between the illumination source and the measuring field and between the measuring field and the camera;
a signal processing platform designed for evaluating at least the pattern image, wherein the pattern image is compared with the pattern to determine a quality factor of the image, and for controlling the wavefront modulator according to its orientation, wherein the wavefront modulator is oriented in a manner which iteratively optimizes the quality factor.

2. The arrangement according to claim 1 , wherein:
the arrangement comprises a first camera and a second camera;
the tracers of the flowing fluid or the pattern are made fluorescent, or the tracers of the flowing fluid and the pattern are made fluorescent, the fluorescence wavelengths being different from each other;
means for wavelength selection are provided in the optical path between the measuring field and the cameras, wherein the means for wavelength selection are configured so that light of a first wavelength is detected predominantly using the first camera and light of a second wavelength is detected predominantly using the second camera.

3. The arrangement according to claim 2 , wherein the means for wavelength selection are adapted as means for the partial reflection of light, the means comprising a mirroring arrangement which acts as a wavelength-dependent beam splitter.

4. The arrangement according to claim 2 , wherein the means for wavelength selection comprise at least one wavelength-independent beam splitter and at least two wavelength-selective filter elements, wherein the wavelengths selected by means of the filter elements are different from each other.

5. The arrangement according to claim 1 , wherein the wavefront modulator is a surface light modulator with a reflective illuminated surface and comprises a combination of a plurality of adaptive optical correction elements.

6. The arrangement according to claim 1 , wherein the signal processing platform comprises an FPGA or a graphics processor or a digital signal processor or a combination thereof.

7. A method for correcting optical disturbances caused by a boundary surface in imaging flow measurement methods for measuring a flowing fluid, wherein the flowing fluid contains tracers designed as scattering particles, and wherein a stationary optical pattern is disposed in the measuring field through which the flowing fluid flows, wherein the flowing fluid is illuminated with an illumination source, the control of a wavefront modulator disposed in the optical path between the measuring field and a camera, wherein the camera is used for recording the flow pattern as an image of the light scattered by the tracers in the flowing fluid and for recording the pattern image as an image of the light scattered by the stationary pattern, or in the optical path between the illumination source and the light source, or in the optical path between the illumination source and the measuring field and between the measuring field and the camera being done in such a way as to iteratively optimize a quality factor determined by comparing the pattern image with the pattern.

8. An arrangement for correcting optical disturbances caused by a boundary surface in imaging flow measurement methods for measuring a flowing fluid, said flowing fluid containing tracers designed as fluorescent particles, the arrangement comprising
at least one illumination source designed to illuminate a measuring field through which the flowing fluid flows with light of at least one illumination wavelength through the boundary surface;
a wavefront sensor adapted to detect the light of the at least one illumination wavelength reflected from the boundary surface according to Fresnel's formulas;
a camera adapted to record the flow image as an image of the light scattered by the tracers of the flowing fluid at a wavelength which differs from the illumination wavelength;
means for partial reflection disposed in the optical path between the measuring field and the wavefront sensor and between the measuring field and the camera, said means comprising a mirroring arrangement acting as a wavelength-dependent beam splitter, wherein the light of the at least one illumination wavelength is deflected predominantly in the direction of the wavefront sensor, and light of a wavelength different from the at least one illumination wavelength is deflected predominantly in the direction of the camera;
a controllable wavefront modulator disposed in the optical path between the measuring field and the camera and between the measuring field and the wavefront sensor, or in the optical path between the illumination source and the measuring field, or in the optical path between the illumination source and the measuring field and between the measuring field and the camera and between the measuring field and the wavefront sensor;
at least one signal processing platform designed for evaluating at least the data detected by the wavefront sensor to determine the wavefront distortion due to the optical disturbance caused by the boundary surface and for controlling the wavefront modulator;
wherein the wavefront modulator is controlled by the signal processing platform in such a way that the determined wavefront distortion is corrected by way of interaction with the wavefront modulator.

9. The arrangement according to claim 8 , wherein the flowing fluid contains tracers designed as scattering particles, wherein the arrangement is designed such that the measuring field through which the flowing fluid flows is illuminated through the boundary surface with light of a first illumination source at an illumination wavelength and the scattering particles are illuminated with light from a second illumination source at a wavelength which is different from the illumination wavelength, the camera being adapted to record the flow image as an image of the light with the wavelength different from the illumination wavelength which is scattered by the scattering particles of the flowing fluid, and wherein the means for partial reflection disposed between the measuring field and the camera are designed as a beam splitter.

10. The arrangement according to claim 8 , wherein the wavefront sensor comprises a sensor of the Hartmann-Shack type.

11. The arrangement according to claim 8 , wherein the wavefront sensor comprises an arrangement for performing holography.

12. The arrangement according to claim 8 , wherein the wavefront modulator is a surface light modulator having a reflective illuminated surface and comprises a combination of a plurality of adaptive optical correction element

Assignees

• Univ Dresden Tech

Inventors

• Büttner Lars
• Czarske Jürgen
• Teich Martin
• Koukourakis Nektarios

Classifications

• G02B27/0068 Primary

  having means for controlling the degree of correction, e.g. using phase modulators, movable elements (controlling the phase of light using moving or deformable elements G02B26/06) · CPC title

• G01F1/661

  using light · CPC title

• G02B26/06 Primary

  for controlling the phase of light (G02B26/08 takes precedence {, measuring optical phase difference G01J9/00}) · CPC title