Optical methods and means of measuring products. Instruments for measuring optical parameters and characteristics of LEDs. Sources of visible laser radiation

In the method of contactless optical measurement, an object is placed between a laser radiation source and a photodetector, the laser radiation power P is measured, it is compared with a given level P 0 , the laser radiation is optically scanned into a beam of parallel beams in the area where the object is located, and the size of the object is determined by the size of the shadow from the object on the photodetector, adjusting the exposure time of the photodetector according to the magnitude of the difference (P 0 -P). The device for implementing the method includes a laser, a beam-splitting plate, a short-focus cylindrical lens, an output cylindrical lens, a collimating lens, a CCD, an information processing unit, and a threshold photodetector. EFFECT: improved measurement accuracy. 2 n. and 2 z.p. f-ly, 1 ill.

Drawings to the RF patent 2262660

The invention relates to measuring technology, in particular to non-contact optical means for measuring the geometric dimensions of various objects.

A known method of non-contact optical measurement of the size of objects, also called shadow, which consists in placing the object under study between a laser and a multi-element photodetector, scanning laser radiation into a beam of parallel beams in the area of ​​the object and determining the size of the object by the size of the shadow cast by it on the photodetector. Devices that implement the known method - laser shadow meters - consist of a laser radiation source, a lens system that forms a beam of parallel beams from the original beam by optical scanning, and a multi-element photodetector connected to the information processing unit. The number of unexposed pixels on the photodetector on the CCD line determines the size of the object (1, 2).

The use of optical scanning makes it possible to use a multi-element photodetector on a CCD line for continuous reading of information and to collect information within one frame, the duration of which is adjustable over a wide range, up to 0.1 μs. This circumstance makes it possible to use laser shadow meters to measure the parameters of objects moving at high speed.

As a prototype of the claimed technical solution, a method of non-contact optical measurement of the size of objects was chosen, which consists in placing the object under study between the laser and the photodetector, optical scanning of the laser radiation into a beam of parallel beams in the area of ​​the object and determining the size of the object by the size of the shadow from the object on the photodetector. A device that implements the known method consists of a laser source, an optical scanning lens system, a multi-element photodiode array, an information processing circuit, and a computer (3).

The disadvantages of the known method and the device with which the method is implemented are due to the following. The measurement accuracy when using the known method depends primarily on the accuracy of determining the boundaries of the contour of the object under study. Diffraction effects lead to the fact that the transition from light to shadow on the surface of the photodetector is characterized by a certain extent, which for photodetectors used in practice on a CCD line is, as a rule, several pixels. The blurring of the border between light and shadow reduces the accuracy of determining the size of an object, and the influence of this factor will be the greater, the smaller the size of the object.

As shown above, the size of the object is determined by the number of unexposed (darkened) pixels on the CCD line. A pixel is considered dark if the video signal from which is less than a certain threshold.

It can be shown that the size of the part will be determined by the number of pixels on which the voltage U t is greater than the threshold voltage U then

where E max - maximum power of laser radiation;

r is the current radius of the laser beam on the CCD line;

r about - the radius of the laser beam at a point with a power density of radiation in e 2 times less than the intensity at the center;

T ex - exposure time;

RC is a parameter specific to a specific line of CCDs.

It follows from expression (1) that the object size depends both on the laser radiation power and on the exposure time.

During the exposure time, the number of pixels on which U t U then will be determined by the power of the laser radiation, since the illumination of each pixel and, consequently, the rate of charge growth on it depends on the power of the laser radiation. As a consequence, the determined size of the object will depend on the power of the laser radiation. Therefore, in the known laser meter with power fluctuations, the accuracy of determining the size of the object is reduced.

The problem solved by the invention is to improve the accuracy of measurements.

This problem is solved by the fact that in the method of non-contact optical measurement of the size of objects, which consists in placing the object between the source of laser radiation and the photodetector, optical scanning of the laser radiation into a beam of parallel rays in the area of ​​the object and determining the size of the object by the size of the shadow from the object on the photodetector, measure laser radiation power R, compare it with a given level R o and by value (P o -R) adjust the exposure time of the photodetector. A device for implementing the method, comprising a laser beam source, laser beam optical scanning means, a photodetector connected to the first input of the information processing unit, and an object located between the laser beam source and the photodetector, is equipped with a beam splitter placed between the laser beam source and the optical scanning means, and a photodetector threshold device, the output of which is connected to the second input of the information processing unit. Means of optical scanning of the laser beam are made in the form of cylindrical lenses, and the beam splitter is in the form of a translucent plate.

The invention is illustrated in the drawing, which schematically shows the device with which the proposed method is implemented. It includes a laser 1, a beam-splitting semi-transparent plate 2, means for optical scanning of the laser beam, consisting of a short-focus cylindrical lens 3 and an output cylindrical lens 4, a collimating lens 5, a photodetector on a CCD line 6 connected to the first input of the information processing unit 7, and a photoreceiving threshold device 8 connected to the second input of block 7 and representing a photodetector with a comparison circuit. The beam splitter 2 and the threshold photodetector 8 form a channel for adjusting the exposure time. The beam-splitting plate 2 is located at an angle to the laser beam trajectory 1 in order to ensure the removal of part of the radiation power to the threshold photodetector device 8. The measured object 9 is placed between lenses 4 and 5.

The inventive method is carried out as follows. The laser radiation 1 hits the beam-splitting plate 2. Part of the radiation is deflected by the plate 2 to the photodetector threshold device 8, and the rest passes into the optical system of lenses 3 and 4, which scan the radiation into a beam of parallel beams. As a result, the object 9 under study is illuminated by a flat beam and an image of the object is formed on the photodetector 6, corresponding to the shadow cast by the object 9 on the surface of the photodetector 6. In block 7, the image signal is processed and the size of the object 9 is determined. In the threshold device 8, a part of the laser radiation power is compared received by the device 8, with a threshold value corresponding to a given radiation power. If the power value is different from the specified one, a difference signal will be generated at the output of the threshold device 8, fed to the second input of block 7. In accordance with the value of the received signal, block 7 adjusts the exposure time of the photodetector 6. If the actual laser radiation power is greater than the specified one, block 7 reduces exposure time, if less - increases.

As a result, the adjustment of the pixel charge time even under conditions of fluctuations in the laser radiation power ensures high measurement accuracy.

Thus, the inventive method and device, by adjusting the exposure time depending on the power of the laser radiation, provide - in comparison with the prototype device - an increase in the accuracy of measuring the size of objects.

LITERATURE

1. A. Z. Venediktov, V. N. Demkin, D. S. Dokov, A. V. Komarov. The use of laser methods to control the parameters of the automatic coupler and springs. New technologies - railway transport. Collection of scientific articles with international participation, part 4. Omsk 2000, pp. 232-233.

2. V.N.Demrin, D.S.Dokov, V.N.Tereshkin, A.Z.Venediktov. Optical control of geometrical dimensions for railway cars automatic coupling. Third Intern. Workshop on New Approaches to High-Tech: Nondestructive Testing and Computer Simulations in Science and Engineering. Proceedings of SPAS, Vol. 3. 7-11 June 1999, St. Petersburg, p. A17.

3. V. V. Antsiferov, M. V. Muraviev. Non-contact laser measurement of the geometric dimensions of bearing rollers. New technologies - railway transport. Collection of scientific articles with international participation, part 4. Omsk 2000, pp. 210-213 (prototype).

CLAIM

1. A method for non-contact measurement of the size of objects, which consists in placing an object between a laser radiation source and a photodetector, optical scanning of laser radiation into a beam of parallel beams in the area where the object is located, and determining the size of the object by the size of the shadow from the object on the photodetector, characterized in that the power is measured laser radiation R, compare it with a given level R o and by value (P o -R) adjust the exposure time of the photodetector.

2. A device for non-contact optical measurement of the dimensions of objects, containing a source of a laser beam, means of optical scanning of the laser beam, a photodetector connected to the first input of the information processing unit, and an object located between the means of optical scanning of the laser beam and the photodetector, characterized in that it is equipped with a beam splitter placed between the source of optical radiation and the means of optical scanning and optically connected to the photodetector threshold device, the output of which is connected to the second input of the information processing unit.

3. The device according to claim 2, characterized in that the means of optical scanning of the laser beam are made in the form of cylindrical lenses.

4. The device according to claim 2, characterized in that the beam splitter is made in the form of a translucent plate.

Of these, the most common optimeters are vertical and horizontal. These devices are used for relative measurements using gage blocks.

The measuring device is an optimeter tube based on a combination of the autocollimation principle with a swinging mirror.

The principle of autocollimation is based on the ability of the lens to convert a beam of diverging rays into a beam of parallel rays, and then collect this beam reflected by a flat mirror at the same focus of the lens.

Rice. 6.12. Ray path in the optical system: a- when located on the main optical axis; b - when the light source is displaced relative to the main optical axis; in- when reflected from the plane of a mirror located at an angle

If the light source is O (Fig. 6.12, a) is in the focus of the lens, then the beam coinciding with the main optical axis will pass through the lens without refraction, and the remaining rays after refraction in the lens will pass parallel to the main optical axis. Having met on the way a mirror plane perpendicular to the main optical axis, the rays will be reflected from it and will again gather at the focus of the lens O.

If the light source O is located not in the focus of the lens, but in the focal plane at a distance a from the main optical axis (Fig. 6.12, b), then parallel rays, leaving the lens and meeting on their way a mirror located at an angle of 90 ° to the main optical axis, will be reflected from it at an angle y to this axis, pass through the lens and converge at point O, symmetrical to point O.

If the light source is located at the focus of the lens, but the mirror plane is at an angle a to the main optical axis (Fig. 6.12, in), then the rays, reflected, will pass at an angle of 2cx to the main optical axis and, refracted in the lens, converge at a point O, located at a distance from the point O t= Ftg2a.

In the design of the optimeter tube, all the described schemes are used.

Rice. 6.13.

• 1 - scale; 2 - prism; 3 - mirror; 4 - prism; 5 - lens;
• 6 - mirror; 7 - fixed support; 8 - measuring rod

The optical scheme of the optimeter tube is shown in fig. 6.13.

Rays of light from a source are directed by an illuminating mirror 3 and prism 2 on the scale 1, on which ±100 divisions are plotted with an interval with= 0.08 mm, located in the common focal plane of the objective 5 and the eyepiece. After passing through the scale, the rays enter the prism 4 and, refracted at an angle of 90°, pass through objective 5. Leaving the objective as a parallel beam, the rays are reflected from mirror 6 and return to the focal plane of the objective with a horizontal shift relative to the main optical axis. The horizontal offset is used to view the image of the scale separately from the scale itself. Mirror 6 has three points of support: two fixed 7 and one movable - measuring rod 8.

Moving the measuring rod 8 by the amount S cause the mirror to turn 6 by an angle a, which will entail a rotation of the rays reflected from the mirror by an angle 2a. In this case, the scale image will generally move in the vertical direction relative to the fixed index by the amount t. The optimeter uses an optical lever, the small arm of which is the distance a from the fulcrum of the swinging mirror 6 to the axis of the measuring rod 8, large - lens focal length F. A feature of the optical lever is that the gear ratio is equal to twice the ratio of its shoulders:

where S- displacement of the measuring rod equal to atgcx.

At the optimeter F= 200 mm and shoulder a = 5 mm. If we accept because of the smallness of the angles tg2a = 2a and tga= a, then

those. when the measuring rod is moved by 1 µm, the scale image will move to the division interval (c = 80). Value k= 80 - own gear ratio of the optimeter lever-optical system. Overall ratio of the optimeter at 12x eyepiece magnification

Designed to measure linear and angular dimensions by direct evaluation.

In modern measurement practice, the microscope of a small model of the IT type and a large model of BMI are most often used.

Rice. 6.14.

• 1 - base; 2 - micrometric screw of transverse movement; 3 - table rotation screw; 4 - frame with centers; 5 - center; 6 - tube;
• 7 - removable eyepiece head; 8 - screw (handwheel); 9 - speaker; 10 - locking screw; 11 - column rotation axis; 12 - lighting device; 13 - column tilt screw; 14 - micrometric screw of longitudinal movement; 15 - table; 16 - handle

The visible division interval c" will actually be 960 μm. Therefore, the division value of the optimeter

The instrumental microscope of a small model (Fig. 6.14) consists of the base of the instrument 1, columns 9, removable eyepiece head 7, tube 6, moving up and down the column 9, table 15, having transverse and longitudinal movement with micrometric screws 2 and 14 respectively, and the lighting device 12.

Speaker 9 can rotate around a horizontal axis 11 s screws 13, deviating from the vertical position in both directions by 10 °. Rough movement of the tube along the column is carried out by hand. It is fixed in any position with a locking screw. 10. Handwheel for precise height adjustment 8.

The longitudinal and transverse movement of the table is counted on the scales of a micrometer screw, similar to a micrometer. The measurement limit for microscrews is 25 mm. The measurement limit in the longitudinal direction can be increased by moving the table with the handle 16, additionally by 50 mm due to the block of end measures installed between special stops. Limits of measurement on an angular scale 0-360 °.

A frame is placed on the microscope table 4 with 5 centers for mounting cylindrical parts with center holes. To measure centerless parts, the frame is removed and a V-shaped prism is then used. Flat parts are mounted directly on the table, which can be rotated around the axis with a screw to a small extent. 3 mainly when setting up the device.

In the instrumental microscope, a removable universal eyepiece head 7 is used, which has two eyepieces - a visual eyepiece B and a reading of angular values ​​A. In the eyepiece B, an image of the shadow contour of the measured object and a dashed grid printed on a glass disk, which rotates using a special flywheel, are observed. The angle of rotation of the dashed grid is counted on the scales (visible in the eyepiece A): movable degrees and fixed minutes with a division value of 1 minute.

interferometers, Based on the use of the phenomenon of interference of light waves, they are divided into contact and non-contact, vertical and horizontal.

Contact interferometers are produced with a variable division value from 0.05 to 0.2 microns. Before measuring, the device is adjusted to the division price r. For this, the division price is set by an arbitrary number of bands To in monochromatic light and determine the number of scale divisions t, in which to put To bands to get the given division price. Recommended at a division value of 0.05; 0.1 and 0.2 µm choose number To= 8; 16 and 32 respectively:

where X- wavelength of light (usually marked on the interferometer).

Interferometers are used mainly for verification of gauge measures and for accurate measurements.

Rice. 6.15.

• 1 - lamp; 2 - condenser; 3 - diaphragm; 4 - light filter;
• 5 - mirror; 6 - plate; 7 - lens; 8 - mesh cavity;
• 9 and 10 - eyepiece; 11 - compensator; 12 - mirror

The optical scheme of the interferometer tube is shown in fig. 6.15. light from the lamp 1 sent by condenser 2 through the diaphragm 3 on a translucent separating plate 6. Part of the light will pass through the plate 6, compensator 11 on the mirror 12 and, reflected from the mirror, will return to the plate again 6. The other part of the light beam will be directed to mirror 5 and, after reflection, will also return to the plate. Met at the plate 6, both parts of the light beam interfere with a small path difference. Lens 7 projects into the grid cavity 8 interference fringes, which, together with the scale printed on the grid, are observed through the eyepiece system 9 and 10. When the filter is turned on 4 an interference pattern is observed, the black strip of which serves as a pointer when reading on a scale.

An optical measuring device in mechanical engineering, a measuring instrument in which sighting (combining the boundaries of a controlled size with a line of sight, crosshairs, etc.) or determining the size is carried out using a device with an optical principle of operation. Three groups of optical measuring instruments are distinguished: instruments with an optical sighting method and a mechanical (or other, but not optical) method of measuring movement; devices with an optical method of sighting and counting of movement; devices that have mechanical contact with the measured object, with an optical method for determining the movement of contact points. X-ray machine Arina-1.

Of the devices of the first group, projectors have become widespread for measuring and controlling parts with a complex contour and small dimensions (for example, templates, clockwork parts, etc.). In mechanical engineering, projectors with a magnification of 10, 20, 50, 100 and 200 are used, having a screen size from 350 to 800 mm in diameter or on one of the sides. Projection nozzles are installed on microscopes, metalworking machines, and various devices. Instrumental microscopes are most commonly used to measure thread parameters. Large models of instrumental microscopes are usually equipped with a projection screen or binocular head for easy viewing.

The most common device of the second group is the UIM universal measuring microscope, in which the measured part moves on a longitudinal carriage, and the head microscope moves on a transverse one. The sighting of the boundaries of the surfaces to be checked is carried out using a head microscope, the controlled size (the amount of movement of the part) is determined on a scale, usually using reading microscopes. In some models of UIM, a projection-reading device is used. The interference comparator belongs to the same group of devices.

Devices of the third group are used to compare measured linear quantities with measures or scales. They are usually combined under the general name of comparators. This group of devices includes an optimeter, an opticator, a measuring machine, a contact interferometer, an optical length gauge, etc. with measuring rod. The movement of the rod during the measurement causes a proportional movement of the interference fringes, which is read off the scale. These devices (horizontal and vertical type) are most often used for relative measurements of the lengths of end measures during their certification. In the optical length gauge (Abbe length gauge), the reading scale moves along with the measuring rod. When measuring by the absolute method, the size equal to the movement of the scale is determined through the eyepiece or on the projection device using a vernier.

A promising direction in the development of new types of optical measuring instruments is to equip them with electronic reading devices, which make it possible to simplify the reading of readings and sighting, to obtain readings averaged or processed according to certain dependencies, etc.

The article is devoted to the devices developed by OOO NTP TKA for measuring the main light and energy parameters and characteristics of optical radiation sources, including LEDs.

The need for prompt and reliable measurement of the main light and energy parameters and characteristics of radiation sources in the visible region of the spectrum, such as chromaticity coordinates, correlated color temperature, ripple coefficient, brightness, illumination and irradiance, is obvious. It is dictated by the rapid development of alternative sources of optical radiation (LEDs), the emergence of various options for displays and light displays, as well as technological processes using sources of optical radiation.

Some features of the construction of devices for measuring the main luminous characteristics of light sources

Measuring illumination and brightness is a simple photometric procedure. At the same time, when designing and manufacturing luxmeters and luminance meters, one has to face quite serious problems in ensuring that the manufactured devices comply with the requirements of regulatory documents.

So, for example, photodetectors (PDs), being the main part of the device for measuring optical radiation, must meet a number of electrical and photometric requirements, depending on the field of application and purpose. In the development and production of devices for measuring radiation parameters, it is necessary to know these requirements, their features, the difficulties of creation, and ways to overcome them.

A device for forming a spatial characteristic (input device) forms an angle of view, the value of which is determined by the purpose of the developed device. So, for example, the input device of a light meter or a heart rate meter is calculated based on the following considerations.

Illumination of a surface created by a point source of radiation, arbitrarily located at an angle. to its normal (Fig. 1), is determined by the expression:

Е = Е 0 ×сosβ, (1)

where E 0 is the illumination created by a point source located normally relative to the surface; β is the angle between the normal and the direction to the source.

Rice. 1. Arbitrarily located source

Obviously, measurements of an instrument that measures illumination must obey the same law. It is impossible to implement this condition in practice without taking certain measures due to the dependence of the reflection coefficient of the surface of the optical elements of the receiving system on the angle of incidence of radiation, described by the Fresnel formula (2). To fulfill this condition, it is necessary to include in the optical scheme of the photodetector the so-called cosine nozzle, which forms the required angle of view and compensates for the error introduced by the surface reflection of optical elements.

The most optimal cosine nozzle for working means (Fig. 2) for measuring optical radiation is an element made of milky glass that uniformly scatters incident radiation in all directions, thereby ensuring the fulfillment of Lambert's law, according to which the brightness of the light-scattering surface is the same in all directions.

Rice. 2. Cylindrical cosine nozzle for working tools

The surface of materials used in input devices reflects incident radiation according to Fresnel's law:

where φ 1 is the angle between the light beam incident on the surface and the normal; φ 2 - the angle between the refracted beam and the normal. Graphically, this dependence is shown in fig. 3.

Rice. 3. Dependence of the reflection coefficient of the material surface on the angle of incidence

This means that the photodetector detects radiation that does not correspond to relation (1) at angles greater than 60°, i.e., different from real radiation.

To compensate for the loss of reflected radiation, the side face of the disk made of milk glass is used. The magnitude of the radiation flux that has passed into the glass through the side faces is proportional to the magnitude of the cylindrical illumination. Under the average cylindrical illumination understand the average illumination of the side surface of a vertically located cylinder. It is defined by the expression:

where β is the angle of incidence of light from a point source onto the side surface of a vertically located cylinder.

The luminous flux Ф falling on the photosensitive element used in the FPU is a function of reflection (ρ) and transmission (τ) of the material used, the illumination of the flat surface (E p) and the cylindrical illumination of the side face (E c):

It is rather difficult to describe this relationship analytically due to the spread of the parameters of the materials used and the geometric dimensions of the elements that make up the FPU. During the development and manufacture of FPU, the optimal combination of characteristics (brand of milky glass, its thickness and the height of the side surface protruding above the body) is empirically found, providing a given error (1–2%), determined by the difference between the obtained spatial characteristic and the theoretical one.

In addition, when creating devices for measuring optical radiation, it is necessary to solve the problem of reducing the spectral characteristic of the sensitivity of a silicon photodiode to the relative light spectral efficiency V(λ), the tabulated values ​​of which are regulated by the decisions of the MKO commission and GOST 8.332.

Spectral correction of the sensitivity of the photodetector Sf(λ) to a given form S(λ) is carried out, as a rule, by color filters. In this case, the transmittance T(λ) is determined by the relation:

There are two main ways to arrange corrective filters in front of the photosensitive element (Fig. 4).

Rice. 4. Ways of arranging corrective filters: a) subtractive; b) subtractive-additive (Dresler's scheme)

In the first case, color filters with suitable spectral characteristics are arranged one after the other. With this arrangement (Fig. 4a), the radiation, before reaching the photodetector, is successively filtered in each filter.

Another way to arrange filters with the required spectral characteristics is shown in Fig. 4b. In this arrangement, called the Dresler layout, some filters are placed next to one another. Different parts of the light flux are passed through the filters in different ways before the flux reaches the receiving area of ​​the photodetector. The resulting spectral transmission curve of the combination can be effectively controlled by changing the relative size of the individual components. Corrective filters made according to this principle can, with a high degree of accuracy, approximate the relative spectral sensitivity of the photodetector to the ideal values ​​of V(λ) at a relatively high transmission at the maxima of the curves. Usually, in practice, in particular, and in the calculation of the devices under consideration, the first method of arranging light filters is used due to its manufacturability and simplicity of calculations.

Let us consider an example of reducing the spectral characteristic of a silicon photodiode Sf(λ) to the relative light spectral efficiency V(λ) (Fig. 5).

Rice. Fig. 5. View of the curves of the spectral sensitivity of the silicon photodiode S(.) and the given measure V(.)

The characteristic S(λ) is reduced to a given curve using a correcting filter, which can be composed of colored glasses (Fig. 6).

Rice. 6. Correction of the spectral sensitivity of the photodetector using color filters

The total transmittance of the correcting filter is calculated by the formula:

where i is the number of colored glasses that make up the light filter, k i (λ) is the absorption index of colored glasses with an index corresponding to the number of colored glass, t i is the thickness of the corresponding colored glasses.

The type of glasses and their number were chosen in a semi-empirical way, based on the availability of produced and available grades. So, for example, for the visible region of the spectrum, the following colored glasses turned out to be suitable for correction: SZS-21, SZS-22, SZS-23, ZhS-20, ZhZS-5, ZhZS-6, OS-5. From the group of blue-green glasses (SZS), SZS-21 was chosen, since it suppresses radiation well in the near-IR spectral region (760–1200 nm), where the maximum sensitivity of silicon photodiodes is observed (λ max = 800–900 nm), selected for correction. Orange glass OS-5 is interchangeable with glass ZhS-20, and yellow-green glass ZhZS-6 is interchangeable with glass ZhZS-5.

The choice of the brand of glasses and their thickness and the calculation of the spectral transmittance of the correcting light filter is carried out in such a way that the following condition is fulfilled at each wavelength: τ(λ)= V(λ)/Sph(λ).

Strict fulfillment of this condition at all wavelengths for serial colored glasses and photodetectors is practically impossible. There will always be a deviation of the actually performed curve S(λ) = Sa(λ)..(λ) from the given one, which must be estimated depending on the purpose and method of calibrating the photometer, where a correcting filter is used.

The photodetector correction error is estimated according to the method developed by CIE (publication No. 53). The calculation of the correction error of the photometric head f 1 (Z) is based on the difference in the response to radiation of an ideal photodetector, the tabulated value of the spectral sensitivity of which is known, and a real photodetector, the relative spectral distribution of which differs from that at which the calibration was made.

where S(λ) is the relative spectral sensitivity of the studied photodetector; SV(λ) - relative spectral sensitivity of the reference photodetector; Фa(λ) - relative spectral distribution of the source "A" at which calibration is performed; Ф i (λ) - relative spectral characteristic of tabulated sources.

Instruments for measuring optical radiation

Luxmeters of the new generation "TKA-Lux" (Fig. 7) and "TKA-PKM-31" are currently the most popular and have metrological characteristics at the level of instruments of the world's best manufacturers of working measuring instruments. Illumination measurement range in the range of 10–200,000 lx with an error of 6–8%.

Rice. 7. Appearance of the light meter "TKA-Lux"

"TKA-Lux/Etalon" is the first Russian luxmeter, the metrological characteristics of which meet the requirements for working standards. It is designed to measure illumination in the visible region of the spectrum 380-760 nm, created by standard sources of optical radiation, located normally relative to the receiver. The luxmeter is intended for the practical implementation of the State verification scheme of means for measuring light quantities in accordance with GOST 8.023-2000. This device, in terms of the accuracy of reproduction and transmission of the dimensions of units of luminous intensity and illumination, provides a metric of precision and working measuring instruments and is distinguished by temporal stability and reliability. The basic relative error of illumination measurement allowed by the device does not exceed 6.0%.

The developed combined device luxmeter + brightness meter "TKA-PKM" (02) is used to measure illumination (in the range of 10–200,000 lux with an error of 8%) and brightness by an overhead method (in the range of 10–200,000 cd/m 2 with an error of 10%) self-luminous extended objects (Fig. 8).

Rice. 8. Appearance of the device "TKA-PKM" mod. 0.2

The device differs from traditional luminance meters by the absence of optical elements (lenses, objective) in the circuit, which greatly simplifies the design and reduces the cost of the device while maintaining its accuracy characteristics.

To remotely determine the brightness of extended sources, an inexpensive device for measuring the brightness of cinema screens, the TKAYAR luminance meter (Fig. 9), has been developed, which meets modern metrological and technical requirements. Aiming at the measured object is carried out using a laser sight.

Rice. 9. Appearance of the TKA-YAR luminance meter

To simplify the design of the device, an unfocused lens was used in the optical scheme. Unregulated focusing at a certain constant distance increases the efficiency of working with the device, since one of the working operations is excluded. In this case, no corrections to the calibration are required, since the readings of the device are proportional to the brightness of the object, regardless of the distance. The device has the following specifications:

• angle of view - 1.0–1.5 °;
• measurement range - 10.0–2000.0 cd/m2;
• spectral correction - 2.0%;
• total error - 10.0%;
• distance to the measured object - not less than 7.0 m.

Measurement of the ripple factor of radiation sources

The emission of light sources when powered from the AC mains (usually at a frequency of 50 Hz) is pulsating. The pulsation frequency in this case is equal to twice the frequency of the supply voltage of 100 Hz. As a criterion for assessing the relative depth of illumination fluctuations as a result of the change in time of the luminous flux of radiation sources when they are powered by alternating current, the illumination pulsation coefficient (Kp) is introduced, expressed by the formula:

where Emax is the maximum value of the amplitude of the change in the illumination component, Emin is its minimum value, Eav is the average value of the illumination (Fig. 10).

Rice. 10. Time response of pulsating illumination

Rice. 11. Appearance of the device "TKA-PKM (08)"

Structurally, the device is made in the form of two blocks: a photodetector part (FPU) and an information processing unit. The information processing unit contains an electronic circuit consisting of an ADC (analogue-to-digital converter), an LCD (liquid crystal display) and an ADuC processor.

The device works as follows. The signal from the FPA is fed to the pre-amplifier, where it simultaneously amplifies the signal and scales it.

The amplified signal is fed to the input of the ADC for conversion to digital form. The digital signal from the ADC output is fed to the microprocessor for further processing. A series of measurements with a period of 10 ms is carried out and the maximum, minimum and average illumination values ​​are determined.

The signal processing is not in phase with the oscillation periods. During the measurement, several periods are analyzed and the values ​​of the sample results are averaged. The result - the values ​​of max, min and average are determined in units of illuminance lx. After finding the signal parameters by formula (8), the value of the ripple coefficient is calculated.

The determination of the pulsation coefficient of radiation sources and illumination is carried out by the TKA-PKM (08) device, the information in it is processed by a microprocessor. This heart rate light meter has the following specifications:

Lever-optical devices include optimeters and measuring spring-optical heads.

Optimeters. Optimeters are divided into vertical (OVO - with an eyepiece and OVE with a projection screen) and horizontal (OGO and OGE). The latter are used to measure both external and internal dimensions. The most common vertical optimeters ( rice. 23,a) with division price 0.001 mm and error of indications ±0.0002 mm used to measure external dimensions (end blocks, plug gauges and highly precise products).

Rice. 23. Vertical optimeter(s), operating principle

tube optimeter (b)

The main reference part of the device is the optimeter tube built according to the lever-optical scheme. The principle of operation of the optimeter tube is shown in fig. 23, b. rays of light 1 guided by a mirror 2 into the slit of the tube and, being refracted by a trihedral prism 3 , pass through the scale marked on the plate 4 . The beam then passes through a total reflection prism. 5 and, reflected from it at a right angle, hits the lens 6 and then on the mirror 7 . Mirror 7 spring 8 pressed against the measuring rod 9 , and when the measuring rod is moved, the mirror rotates around an axis passing through the center of the ball 10 . The angle of rotation of the mirror depends on the tilt of the mirror 7 . On fig. 23, b shows the course of one incident beam (solid line) and reflected (dash - dotted line). The angle between these rays is 2 .

The reflected beam of rays by the lens is converted into a converging beam of rays, which gives the image of the scale. Installation of the device tube on the block of end measures consists in combining the zero stroke of the scale with a fixed pointer. When moving from the measuring rod by 1 µm, the scale image shifts in the field of view by 1 division relative to the fixed pointer.

Measuring spring-optical heads. These devices have an abbreviated name - opticators. They use the spring principle of the microcator, only the coiled spring is attached not to an arrow, but to a mirror, on which a beam of light falls and is reflected on a glass scale, where an image of an index stroke appears. Produced spring-optical heads, designated OP, have a connecting diameter 28 mm and are designed for accurate linear measurements when fastened in racks of heavy mud. The measuring heads have a scale rotation for fine adjustment to the size and tolerance field indicators in the form of colored curtains on the path of the light beam (bunny) coloring it green or red. Spring optical heads are produced in submicron (models 01P, 02P and 05P) and micron (P1, P2 and P5) with an increased interval between scale divisions to facilitate reading.

Pneumatic length gauges for low and high pressure.

The operation of pneumatic measuring instruments - length gauges is based on the property of the outflow of air at a constant pressure from a small hole called a nozzle. The scales of pneumatic instruments are graduated not in pressure units, but in linear units (for example, in micron). Such a calibration allows you to directly read the deviations of the dimensions of the parts being checked from the size of the reference part or measure, according to which the device is configured and to determine the deviations from the correct geometric shape of the products. Two types of devices are used in factories: low-pressure devices based on changes in air pressure ( rice. 24,a), and float (rotameters), based on the change in air flow ( rice. 24b).

Rice. 24. Pneumatic length gauges:

a - with a liquid pressure regulator; b - float device;

c - plug in the hole (section)

Low pressure devices available with two or more scales for simultaneous or separate measurement of two or more sizes. On the rice. 24,a shows a device with two cut-off scales and a measuring plug with a reference ring for setting the device to zero. The measurement limits can be changed from 0,02 before 0.20 mm, since they depend on the size of the nozzles that are used in the device. At the measurement limit 0.02mm the marginal error of indications is equal to 0.0005 mm, and at the highest measurement limit 0.20 mm the error, respectively, is equal to 0.005 mm.

Most common float pneumatic length gauges(Fig. 24b).

The principle of operation of these devices is based on changing the air flow rate in a conical glass tube. Air from a pressurized power supply 300-600 kPa (3-6 kgf / cm 2) passes through the sump, filter and reducing stabilizer 1, which equalizes the air pressure, then enters the conical glass tube 2. The working air pressure can vary from 70 before 200 kPa(from 0,7 before 2 kgf / cm 2). When setting up the device, they ensure that the metal light float 3 (weight less than 1 g) was in suspension at the mark 0 scales 4 . when measuring parts, depending on the gap change ( rice. 24, in) between the outlet nozzle and the surface of the product to be measured ( see fig. 24b) the air flow changes, and, consequently, the position of the float is set relative to the scale marks 4. with a large gap, the air flow is greater, and the float 3 rises, with a smaller gap, the flow is less, and the float falls. The division value depends on the calibration and settings of the device and can be equal to 1-2 µm and even fractions of a micrometer.

Before measuring the diameters of the holes using a pneumatic device, a plug of a special design is inserted into the exemplary ring and, by adjusting the air supply with the help of screw 5, the float 3 in the tube 2 is set to the zero position. If the size of the hole of the tested part differs from the size of the reference ring or block of tiles, the float will show a deviation from the size.

Turning the plug in the hole to be checked on 90, 180 and 270° in one and different sections along the axis of the part, it is possible to determine the deviations of the parts from the correct geometric shape.

Pneumatic instruments are especially indispensable in determining the diameters and shape deviations of holes, especially deep and non-through holes, as well as holes of small diameter.

Caliber

In the mass production of products, when the factory is forced to measure parts on the same size every day, tools of a rigid design are widely used - limit gauges (Fig. 25): plugs for controlling holes ( rice. 25, a, b) and clamps for shaft control ( rice. 25, c, d). Gauges do not have reading devices for sizing, they can only be used to determine whether the actual size of the part is within tolerance or not. To do this, calibers are made according to the maximum dimensions of the part being checked. One side of the plug (elongated) will have a nominal size and be called the through passage PR, and the other side of the plug (shortened) will have the nominal size of the largest hole. This side of the plug is called non-through and is designated NOT, it can only enter a part that has an oversized hole. Such details are rejected.

The part control process consists in simply sorting them with the help of two limit gauges into three groups: good parts, the size of which is within the allowable limits (PR passes; and NOT does not pass); the marriage is correctable when the size of the shaft is greater than the permissible one, and the size of the hole is less than the permissible one (PR does not pass); the marriage is irreparable when the size at the shaft is underestimated, and at the hole it is overestimated (DOES NOT pass).

Gauges used by QCD workers and inspectors to check parts are called working gauges; their types, sizes and specifications are standardized.

Rice. 25. Gauges.

a - double-sided plug, b - single-sided plug, c - double-sided bracket,

g - limit adjustable bracket

Gauges for holes up to 50 mm are made in the form of full plugs ( Fig. 25, a), for holes above 50 before 100 mm both full plugs and incomplete plugs can be used ( rice. 25b), but above 100 mm- only incomplete. For larger sizes over 360 mm instead of plugs, spherical bore gauges are used.

Gauges-brackets for shafts are most often used one-sided limit whole or double-sided sheet ( rice. 25, in). For shaft sizes from 100 before 360 mm use one-sided limit brackets with plug-in jaws ( rice. 25,g). The following designations (marking) are applied to the gauges: the nominal size of the controlled part, the designation of the tolerance field of the part and the accuracy class (qualitation), digital values ​​​​of the maximum deviations of the part in millimeters, the designation of the sides of the gauge - through passage PR and impassable NOT, trademark of the manufacturer. For passing calibers, the standards provide tolerances for manufacturing and wear, and for non-through gauges - only manufacturing tolerances. Standard deviations for the manufacture and wear of calibers are counted from the limiting dimensions of shafts and holes; for through-through brackets - from the largest limit size of the shaft, and for through-hole plugs from the smallest limit size of the hole; for non-through calibers, on the contrary - from the smallest shaft size and the largest hole size.

ST SEV 157-75, “Smooth gauges for sizes up to 500 mm. Tolerances”, provides for a special procedure for determining the limiting (executive) dimensions of through gauges, Z and Z1- these are deviations of the middle of the tolerance field for the manufacture of through gauges ( Z for hole and Z1 for a shaft) relative to the smallest hole size and the largest shaft size limit; H and H 1– tolerances for the manufacture of pass and non-pass gauges (for holes H and shaft H 1); Y and Y 1- permissible exits of the worn caliber beyond the tolerance field (holes Y and shaft Y 1).

For calibers with dimensions over 180 mm, there are also caliber control error compensation values ​​indicated for holes and for the shaft.