RU2315286C1 - Video refractometer - Google Patents

Abstract

FIELD: measuring technique.

SUBSTANCE: video refractometer can be used for measuring refractivity of gases, liquids, glasses and other transparent media. Video refractometer has photoreceiver made in for of television camera. Light-emitting diodes 5 are mounted onto case of TV camera. Light-emitting diodes are disposed along circle. Center of circle belongs to optical axis of TV camera. Video refractometer also has registration device 7 and mirror 6. TV camera has case 1, electric plate 2, CCD array 3 and objective 4, Mirror 6 is mounted in front of TV camera in perpendicular to its optical axis at distance defined by formula S=(f(D-d)/2M)/n_max, where n_max is maximal coefficient of refractivity of tested medium placed between TV camera and mirror; f is focal length of objective of camera; D is diameter of circle onto which circle the light-emitting diodes are mounted; d are diameters of light-emitting diodes, M is minimal size of photosensitive area of CCD array.

EFFECT: improved precision of measurement; ability of making measurements due to submerge of video refractometer in tested fluids or gases.

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Description

The invention relates to the field of measuring equipment and, in particular, for measuring the refractive index of liquids, gases, glasses and other optically transparent media.

The refractive index characterizes the properties of media through which light passes, its value depends on the wavelength of light and is calculated by the formula / 1 /:

where i and r are the angles of incidence and refraction of light at the interface of two media, respectively.

Known Abbe refractometer containing a light source directed to the boundary of two media, and a telescope mounted at certain angles to the border of the media / 2 /. The refractive index is measured on a scale related to the angle of rotation of the telescope, the measurement error does not exceed 0.1%.

The closest to the claimed invention in terms of features (prototype) is an IRF-454B2M refractometer containing a light source directed to the media boundary and a light receiver in the form of a telescope mounted at a measured angle to the media boundary / 3 /. It serves to determine the refractive index of a liquid, in particular oil. A drop of the test liquid is introduced into the optical system of the refractometer, and the refractive index is determined by the angular position of the telescope.

The prototype has the following disadvantages:

- the refractive index is determined for a small amount of liquid (drop of liquid) and it may differ from the bulk of the liquid, which serves as a source of measurement error;

- during the measurement, light oil fractions evaporate, which serves as an additional source of measurement error;

- measurements are associated with the movement of the telescope and the visual reading of the instrument, which limits the accuracy of the measurements;

- the prototype, due to its design features, does not allow to measure the refractive index of gases and glasses.

The problem solved by the present invention is to eliminate these disadvantages by:

- exceptions to the design of the device moving nodes;

- taking measurements in an automated mode;

- taking measurements, in addition to liquid, also for gases and glasses.

To solve this problem, in the proposed video refractometer containing a light source, a photodetector and a recording device, in accordance with the invention, and in contrast to the prototype, the photodetector is made in the form of a camera with a CCD matrix, the light source contains at least three LEDs placed around the circumference of the camera , the center of which is located on the optical axis of the camera, in addition, the video refractometer is equipped with a mirror mounted in front of the camera perpendicular to its optical axis at a distance determined by formula is

where n _max - the maximum refractive index of the investigated medium, placed between the camera and the mirror;

f is the focal length of the camera lens;

D is the diameter of the circle on which the LEDs are mounted;

d are the diameters of the LEDs;

M is the minimum size of the photosensitive region of the CCD.

The invention is illustrated in the drawing, which, as an example, shows a diagram of a video refractometer containing 8 LEDs.

The drawing shows: the camera body 1, the electronics board 2, the CCD matrix 3, the lens 4, LEDs 5, mirror 6 and video frame 7.

The camera itself contains a housing 1, an electronics board 2 and a lens 4. On the housing 1, LEDs 5 are installed, located on a circle, the center of which is on the optical axis of the camera.

In front of the camera perpendicular to its optical axis at a distance S, determined by the above formula, a mirror 6 is installed.

The test medium (gas, liquid, glass) is placed between the mirror and the camera.

Video refractometer works as follows. The light from the LEDs 5 passes through the medium under study, is reflected from the mirror 6, and with the aid of a lens 4 it focuses on the CCD matrix 3. As a result, a video signal is formed on the electronics board 2 based on the signals of the CCD matrix 3, containing the images of the LEDs 5 in the video frame 7.

If there is a vacuum between the camera and mirror 6, then the images of the LEDs in the video frame 7 will be located on the circle of the minimum diameter D ₀ . If the medium under investigation is placed between the camera and mirror 6, then they will be located on a circle with a large diameter D.

The ratio D / D _{0 is} proportional to the desired refractive index of the investigated medium, which serves as the basis for measurements.

Measurements are performed by processing the mentioned video signal in a recording device, not shown in the drawing, which is a computer with the appropriate computer program.

Measurements are performed in the following sequence:

- A video refractometer is placed in a medium with a known refractive index (for example, a vacuum with n = 1). The value D _{0 is} determined and stored in the computer.

- The video refractometer is immersed in the test medium and the desired refractive index of this medium is determined relative to the reference one by computing by the formula:

where k is the metrological constant determined on the basis of calibration measurements.

The results of experimental studies of the layout of a video refractometer showed the ability to perform measurements with a relative error of 0.01% or less.

Based on a video refractometer, a number of devices can be created for the express analysis of oil products and other process liquids in the oil refining, chemical and other industries.

Claims (1)

A video refractometer containing a light source, a photodetector and a recording device, characterized in that the photodetector is made in the form of a camera with a CCD matrix, the light source contains at least three LEDs placed on the camera body in a circle, the center of which is on the optical axis of the camera, in addition , the video refractometer is equipped with a mirror mounted in front of the camera perpendicular to its optical axis at a distance determined by the formula

where n _max - the maximum refractive index of the investigated medium, placed between the camera and the mirror; f is the focal length of the camera lens; D is the diameter of the circle on which the LEDs are mounted; d are the diameters of the LEDs; M is the minimum size of the photosensitive region of the CCD.