Instruments for measuring optical parameters and characteristics of LEDs. Optical measuring instrument Optical measuring instruments

Using optical instruments that provide a real image of an object and have plates with divisions or crosshairs in the image plane, measurements can be made in two ways.

1. The optical system, together with the line plate rigidly connected to it, can move relative to the object. The accuracy of sighting is mainly determined by the magnification provided by the microscope. The amount of movement is the measured value of the size. The measurement error is included entirely in the measurement result.

2. The optical system is stationary. The line system either moves in the image plane of the object relative to the image itself, or has a scale. The measuring tool is an optical system. The accuracy of sighting (contact) with the measured surface is the same as in the first case. The amount of movement of the line plate corresponds to the dimensions of the actual image. Therefore, the measurement result includes an image scale error, so it must be accurately known, and the image is strictly similar to the object.

Optical instruments are divided into three types:

1) devices with an optical sighting method with a measured surface and mechanical measurement of the movement of the sighting point;

2) devices with mechanical contact with the controlled product and optical measurement of the movement of the point of contact;

3) devices with an optical device for observing the controlled product and optical measurement of the movement of the point of view.

Instruments of the first type include instrumental microscopes and projectors.

Instrumental microscopes are intended for measuring external and internal linear and angular dimensions of products in rectangular and polar coordinates. They consist of the head of the main microscope and a device with the help of which either the head itself or the controlled product can move in one or two mutually perpendicular directions. In many microscope designs, the ocular line plate can be rotated, allowing both linear and angular measurements to be made. The amount of movement of the measuring table is determined using an eyepiece micrometer, gauge blocks or line gauge. Readings on scales are most often made using reporting eyepieces with fixed divisions. Most often, thread parameters are measured using instrumental microscopes.

The small model instrumental microscope (MMI) has a measurement range in the longitudinal direction of 75 mm, in the transverse direction – 25 mm. The division price of a threaded micropair of displacement is 0.01 mm. For sizes over 25 mm, gauge length gauges are used.

The large model instrumental microscope (LMI) has a measurement range in the longitudinal direction of 150 mm, in the transverse direction – 50 mm. The division price of a threaded micropair is 0.005 mm, which is achieved by increasing the diameter of the drum. Microscopes have appeared in which the microcouple is equipped with a pulse device with a digital readout.

Projector in mechanical engineering, an optical device is called, in which an optical device forms an image of the measured object on a scattering surface that serves as a screen. The projector is used for monitoring and measuring products with complex profiles, such as profile templates. You can measure the contours of sharpenings, grooves, and the distance between the centers of holes.

There are:

Control of the enlarged actual image projected onto the screen or ground glass;

Measurement using a coordinate measuring table and measuring overlap on the screen.

Devices of the second type are based on obtaining an autocollimation image. Autocollimation is the path of light rays in which they, emerging from one part of the optical system as a parallel beam, are reflected from a flat swinging mirror and pass through the system in the opposite direction. These devices include: vertical and horizontal optimeter; optical length gauge vertical and horizontal; interferometer; measuring machine; goniometer.

Optimeter– a device for measuring linear dimensions by comparison with a measure, gauge or sample part, the converting element in which is a lever-optical mechanism. The measuring head is an optimometer tube of an ocular or projection (screen) type. In an eyepiece-type tube, the size values ​​are measured on a scale observed in the eyepiece; in a projection-type tube, the measurement is made on the screen.

Optimeters are manufactured in two versions - vertical with the same arrangement of the measurement line and horizontal - with a horizontal measurement line. The vertical optimeter is used for contact measurements when monitoring external linear dimensions, and the horizontal one is used for external and internal dimensions.

Optical length gauge- a device for measuring linear dimensions by comparison with a value on a scale built into this device and moving with the measuring rod. Fractional values ​​are counted on a scale using a vernier built into a special eyepiece or projection microscope. Depending on the design of the racks in which long gauges are installed, they, like optimeters, can be vertical or horizontal.

Length gauges on horizontal stands of the IZV type are intended for the same purposes as horizontal optimometers, but measurements here are carried out using the direct method without the use of length gauges. Horizontal length gauge type IKU is designed for measuring external and internal linear and angular dimensions in rectangular and polar coordinates.

Lengths and measuring machines designed for measuring large lengths along one coordinate axis. The measurement error with a length gauge under recommended conditions, including temperature, ranges from 0.001 to 0.003 mm.

Goniometers serve for measuring angles using a non-contact method using an autocollimator directly along the limb. They produce goniometers of the GS-1, GS-2, GS-5, GS-10 and GS-30 types with division values ​​of 1, 2, 5, 10 and 30", respectively.

The device has a rotation axis mounted on supports at the base. A dial, an alias and a stage are attached to the axis of the device. The limb can rotate together with the table or together with the alias. The Aliada has a reading device and a column with a telescope, to which autocollimation eyepieces are attached.

Interferometer– a measuring device based on the interference of light. Contact interferometers are designed to measure outer diameters using glass plates. The measurement range of the vertical interferometer is up to 150 mm, horizontal – up to 500 mm.

The measurement error with a vertical interferometer when using second-digit length gauge blocks ranges from 0.25 to 0.40 µm. These interferometers are most often used to certify gauge blocks for the third category.

Measuring machine- a device for measuring linear dimensions by comparison with a scale built into this device, with the reading of fractional values ​​using an additional scale moving with one measuring tip and along the optimometer tube. The machine has a scale with a large interval, which is divided using an additional scale, and a device for reading values ​​with a division value of 0.0001 mm. Measuring machines are mainly designed for measuring large dimensions (more than 1000 mm) and are of the horizontal type. Measurements on the machine are made using the direct method or the method of comparison with a measure. In the latter case, the deviation from the adjusted size is measured using the scale of the optimometer tube.

Measuring machines are used mainly for large gauge blocks and very often to determine the size of micrometric bore gauges after their assembly. The measurement error using the comparison method with a measure up to 500 mm ranges from 0.0004 to 0.002 mm. When measured by the direct assessment method, i.e. using all scales, the measurement error under recommended conditions ranges from 0.001 to 0.020 µm.

The main representatives of the third type of optical instruments are the universal microscope and the universal measuring microscope.

Universal microscope(UMM) is used to measure linear and angular dimensions in a plane with sighting of measured points or lines using a microscope and reading values ​​on optical scales. UIM is a two-coordinate measuring machine. The position of the longitudinal and transverse slides is determined on glass scales using reading microscopes equipped with eyepieces with a spiral vernier. When measuring threads, measuring knives are often used to improve accuracy.

The UIM has a measurement range in the longitudinal direction of 200 mm, in the transverse direction – 100 mm. The division value of the linear reading devices is 0.001 mm, the goniometric device is 1".

Microscopes are manufactured with a measurement range of 500x200 mm. Some microscopes have a projection device and a digital size readout. Microscopes are equipped with various equipment to carry out a variety of measurements, which is why they are called universal.

Application lasers for linear measurements. The use of lasers, especially gas lasers in the visible range, has enormously expanded the range of applications of optical methods for measuring distances and angles. The spatial uncertainty of the laser light allows beams to be collimated with divergence caused only by diffraction. Thanks to this, laser-based devices provide angular accuracy of about 1 microrad when operating at a distance of about hundreds of meters.

Due to the high intensity of laser radiation, tweezing can be performed by directly sending a beam of light in a given direction, and interferometric measurements can be carried out in a normally lit room and even in the open air.

One of the simplest ways to use lasers is the sighting technique. Having installed the laser, you can walk along its so-called “optical string”, checking the position of the various elements of the controlled structure. The sighting technique is widely used in the assembly and installation of aircraft, petrochemical equipment, ships, during leveling, tunneling, and in the construction of large structures.

The most common laser measurement method is length measurement, using conventional optical interference for short distances and modulated light techniques for long distances. The accuracy of laser devices is determined mainly by the degree of frequency stabilization of the laser used and can actually be on the order of 10 -9 – 10 -10 mm.

Using lasers, it is possible to carry out continuous interoferometric control of the dimensions of parts in the production process. Laser interferometers and digital technology have made it possible to control large-sized products by deviations in size, shape and surface location.

One of the promising directions in the development of linear measurement technology is holographic interferometry using a laser.

In laser interferometers for workshop purposes, a TPL-EOK1 laser displacement meter with automatic control devices and a computer is used. The device has a button for setting the zero position, which makes it possible to carry out measurements using the method of comparison with a standard. The device has a stand and a measuring table, which allows measurements in both vertical and horizontal planes.

6 STANDARDIZATION OF BASIC NORMS OF INTERCHANGEABILITY

An optical measuring device in mechanical engineering, a measuring instrument in which sighting (alignment of the boundaries of a controlled size with a hairline, crosshair, etc.) or size determination is carried out using a device with an optical operating principle. There are three groups of optical measuring instruments: devices 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 movement counting; devices that have mechanical contact with the measured object, with an optical method for determining the movement of the contact points.

X-ray machine Arina-1.

Of the devices of the first group, projectors have become widespread for measuring and monitoring parts with complex contours and small sizes (for example, templates, watch mechanism parts, etc.). In mechanical engineering, projectors are used with magnifications of 10, 20, 50, 100 and 200, having a screen size from 350 to 800 mm in diameter or on one side. Projection attachments are installed on microscopes, metalworking machines, and various instruments. Instrumental microscopes are most often used to measure thread parameters. Large models of instrumental microscopes are usually equipped with a projection screen or binocular head for easy viewing.

Devices of the third group are used to compare measured linear quantities with measures or scales. They are usually combined under the general name comparators. This group of instruments includes an optimeter, an opticator, a measuring machine, a contact interferometer, an optical length meter, etc. A contact interferometer (first developed by I. T. Uversky in 1947 at the Kalibr plant in Moscow) uses a Michelson interferometer, the movable mirror of which is rigidly connected with measuring rod. The movement of the rod during measurement causes a proportional movement of the interference fringes, which is counted on a scale. These devices (horizontal and vertical types) are most often used for relative measurements of the lengths of gauge blocks during their certification. In an optical length gauge (Abbe length gauge), the reading scale moves along with the measuring rod. When measuring using the absolute method, a size equal to the movement of the scale is determined through the eyepiece or on a 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 that make it possible to simplify readings and sighting, obtain readings averaged or processed according to certain dependencies, etc.

In the method of non-contact optical measurement, an object is placed between a source of laser radiation and a photodetector, the power of the laser radiation P is measured, it is compared with a given level P 0 , the laser radiation is optically scanned into a beam of parallel rays 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 difference (P 0 -P). The device for implementing the method includes a laser, a beam splitter plate, a short-focus cylindrical lens, an output cylindrical lens, a collimating lens, a CCD, an information processing unit, and a photodetecting threshold device. The technical result is increased measurement accuracy. 2 n. and 2 salary f-ly, 1 ill.

Drawings for RF patent 2262660

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

There is a known method for non-contact optical measurement of object sizes, also called shadow, which consists of placing the object under study between a laser and a multi-element photodetector, scanning laser radiation into a beam of parallel rays in the area where the object is located, 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 rays from the initial beam by optical scanning, and a multi-element photodetector connected to an information processing unit. The number of unexposed pixels on the photodetector on the CCD array 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 capture information during one frame, the duration of which is adjustable within 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 proposed 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, optically scanning the laser radiation into a beam of parallel rays in the area where the object is located, and determining the size of the object by the size of the shadow of the object on the photodetector. A device that implements the known method consists of a laser radiation 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 a known method depends, first of all, 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 boundary between light and shadow reduces the accuracy of determining the size of an object, and the effect of this factor will be 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 from which the video signal is less than a certain threshold is considered dark.

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

where E max is the maximum power of laser radiation;

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

r o is the radius of the laser beam at a point with a radiation power density 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.

From expression (1) it follows that the size of the object depends on both the laser radiation power and the exposure time.

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

The problem solved by the invention is to increase 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 a source of laser radiation and a photodetector, optically scanning the laser radiation into a beam of parallel rays 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, they measure laser radiation power P, compare it with a given level P o and adjust the exposure time of the photodetector based on the value (P o -P). A device for implementing the method, containing a source of a laser beam, means for optical scanning of the laser beam, a photodetector connected to the first input of the information processing unit, and an object located between the source of the laser beam and the photodetector, equipped with a beam splitter placed between the source of the laser beam and the means of optical scanning, and a photoreceiving threshold device, the output of which is connected to the second input of the information processing unit. The means for 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 by a drawing, which schematically shows a device with which the inventive method is implemented. It includes a laser 1, a beam-splitting translucent 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 photodetector threshold device 8 connected to the second input of block 7 and representing a photodetector with a comparison circuit. The beam splitter plate 2 and the photodetector threshold device 8 form a channel for adjusting the exposure time. The beam splitter plate 2 is located at an angle to the trajectory of the laser beam 1 in order to ensure that part of the radiation power is removed to the photodetector threshold device 8. The measured object 9 is placed between lenses 4 and 5.

The inventive method is carried out as follows. Laser radiation 1 hits the beam splitter plate 2. Part of the radiation is deflected by 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 rays. As a result, the object under study 9 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 portion of the laser radiation power is compared , received by device 8, with a threshold value corresponding to the specified 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, arriving at 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, adjusting the pixel charging time even under conditions of fluctuations in laser radiation power ensures high measurement accuracy.

Thus, the inventive method and device, by adjusting the exposure time depending on the laser radiation power, 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. Application 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 Internat. 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. Muravyov. Non-contact laser measuring 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 the object between a source of laser radiation and a photodetector, optically scanning the laser radiation into a beam of parallel rays 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 P, compare it with a given level of P o and, based on the value (P o -P), adjust the exposure time of the photodetector.

2. A device for non-contact optical measurement of the dimensions of objects, containing a laser beam source, means for 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 for optical scanning of the laser beam and the photodetector, characterized in that it is equipped with a beam splitter located between the source of optical radiation and the optical scanning means and optically connected to a photodetecting 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 for 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.

To objectively assess the quality of construction work and successful subsequent operation of fiber-optic lines, construction and service organizations must have modern measuring equipment that allows measurements with reliable results.

The fleet of control and measuring equipment is diverse and is represented by domestic and imported equipment. The choice of the required measuring equipment depends on the specific task, taking into account the cost of the device (Table 5).

Table 5. Comparison of diagnostic procedures and measuring instruments.

RADIATION SOURCE

Used in conjunction with an optical wattmeter or fiber ID to test the integrity of welds, determine overall optical loss, and identify fibers. Approximate price: $500-2500.

OPTICAL POWER METER

Optical Power Meters (OPM) are used to measure the optical power of a signal, as well as to measure cable attenuation (Fig. 22). These meters are as common a tool for fiber optic engineers as a multimeter is for electronics engineers.

Rice. 22. Optical power meter "GN 6000"

Optical power meters provide both measurement of cable lines and analysis of the operation of terminal equipment transmitting the signal to the optical line.

Paired with a stabilized signal source, OPM provides measurement of attenuation - the main parameter of optical line quality. A particularly important class of measurements for OPM is the measurement of parameters of optical line nodes (cable sections, interfaces, welding nodes, attenuators, etc.).

The main parameters of OPM are:

Detector type;

Amplifier linearity;

Accuracy and schedule of required calibration;

Dynamic range;

Accuracy and linearity of work;

Ability to support various optical interfaces;

Approximate price: 400-1200 $.

ATTITUDE ANALYZER

The Optical Loss Test Set (OLTS) is a combination of an optical power meter and an optical signal source (Fig. 23). There are integrated and separate loss meters.

Rice. 23.

Integrated ones have a signal source and a power meter in one device, while separated meters are a set of a signal source and an ORM. Accordingly, the technical parameters of loss analyzers contain all the listed parameters for signal sources and optical power meters.

Optical power loss analyzers provide step-by-step analysis of the optical transmission line, including cable sections, splices and splices. This primarily concerns separate operational optical power loss analyzers. At the same time, integrated loss analyzers, which are typically used for industrial analysis, offer increased functionality and measurement accuracy. For example, many dual-frequency analyzers can perform measurements at wavelengths of 1310 and 1550 nm automatically.

FIBER DAMAGE DETECTOR

Used in combination with a light source to test fiber integrity and other applications. Lightweight, manual. Approximate price: $600.

FIBER ID

Used to determine the transmission of radiation through an optical fiber. Lightweight, compact, the size of three matchboxes, a field device. These instruments can test fiber integrity, verify cable markings or confirm the presence or absence of a signal before rerouting or maintenance, and insert and exit optical signals through optical fiber bends. Approximate price: $1000-1200

OPTICAL ADJUSTABLE ATTENUATOR

Indispensable in determining error rates in digital systems. Used in conjunction with an optical wattmeter and CO meter. Lightweight, manual.

Approximate price: $1000-3000.

QUALIFICANT OF OPO

Specially designed for determining optical reflection loss. The device includes a calibrated light source, an optical wattmeter and other special components. The device determines OPO more accurately than a conventional optical reflectometer. Approximate price: 1500 - 5000$

FIBER LOCATOR

The device has all the capabilities of an optical reflectometer in terms of determining the distance to the location of damage, is lightweight, compact, easy to use and is intended for use in field conditions.

Approximate price: $2500-5000.

OPTICAL REFLECTOMETER

Optical Time Domain Reflectometers (OTDR) are the most comprehensive instrument for operational analysis of optical cable networks.

The OTDR is a combination of a pulse generator, a splitter and a signal meter and provides reflected power measurements from one end. Reflectometers operate on the radar principle: a short-duration pulse is sent into the line, which propagates along the optical cable in accordance with Rayleigh scattering and Fresnel reflection on inhomogeneities in the optical cable (defects in material, welding, connectors, etc.). The control processor ensures coordinated operation of the laser diode and the electronic oscilloscope, making it possible to observe the backscatter flux in whole or in parts. A directional coupler and an optical connector are used to inject pulses into the fiber. The backscattering flux through an optical connector and a directional coupler enters a highly sensitive photodetector, where it is converted into electrical voltage. This voltage is applied to the Y input of the electronic oscilloscope, causing a deflection of the oscilloscope beam corresponding to the power of the backscatter flux. The X-axis of the oscilloscope is calibrated in distance units, and the Y-axis is calibrated in decibels.

An optical time domain reflectometer (OTDR) is a device that, based on the use of light scattering phenomena, is widely used to measure the attenuation of optical fibers and their connections, the length of optical fibers or fiber lines and the distance to any part of them.

A block diagram of a typical time domain reflectometer is shown in Fig. 24.

Rice. 24.

The operation of the device is based on measuring the power of the light signal scattered by various sections of the fiber-optic line.

Relatively high-power light pulses from a source built into the optical pulse reflectometer are injected into the fiber, and a highly sensitive receiver measures the time dependence of the power of the light signal returning from the test fiber back to the reflectometer.

The time delay of the signal is equal to twice the distance to the test area divided by the group speed of light in the fiber.

The power of the received signal is determined by the backscatter coefficient, the power of the testing light pulse, which decreases as the light travels forward, and the attenuation of the scattered signal on its way back. Therefore, received power is a function of the pulse loss to and from the fiber section under test and the backscatter or reflection coefficient.

In areas of homogeneous fiber where it is reasonable to assume a constant backscatter coefficient, a time domain reflectometer can be used to measure fiber attenuation and loss at discontinuities or line elements, as well as to determine the location of fiber breaks, splices, and connector locations. Besides? The reflectometer provides a graphical representation of the state of the fiber under test. Does it have another advantage over the combination of a light source and a wattmeter? or loss tester: using an OTDR requires access to only one end of the fiber.

In most cases, reflectometers are used to detect faults in installed cables and to optimize connections. However, they are also very useful in inspecting optical fibers and searching for manufacturing defects in them. Is there currently work underway to improve the resolution of reflectometers when working over short distances (in LAN networks) and performing new tasks? like this? as an estimate of the value of losses due to reflection from connectors.

Operation of optical reflectometers.

The main purpose of measurements made using optical reflectometers is to determine the impulse response of the fiber under test. As is known, the pulse transfer characteristic of the device under study can be obtained if an infinitely short pulse is applied to its input. The testing pulse of an optical reflectometer has a finite duration and, therefore, a real time response - the reflectogram is a convolution of the pulse transfer function of the fiber with the testing pulse.

A typical reflectogram of a pulsed reflectometer is shown in Fig. 25.

Rice. 25.

The vertical scale determines the level of the scattered (reflected) signal in logarithmic units. The horizontal axis corresponds to the distance from the reflectometer to the fiber region being tested.

According to Rayleigh's formula, the intensity of light scattering is inversely proportional to the fourth power of the wavelength. The total losses due to Rayleigh scattering can be quantitatively estimated using the formula:

DB/km, (61)

where Kp is the dissipation coefficient, for quartz equal to 0.8 [(μm4? dB)/km];

Wavelength, microns.

In an optical fiber, scattering on impurity particles can be reduced almost to zero, but scattering on “frozen-in” inhomogeneities cannot be fundamentally reduced; it is they that determine the minimum value of scattering losses.

In Fig. 25 also shows signals from connectors, welds, mechanical connections, bend and crack losses and reflections from them.

Connectors. Does the presence of a connector in a fiber-optic line lead to the appearance of a peak in the reflectogram caused by Fresnel reflection at the ends of the connected fibers? and a decrease in the magnitude of the scattered signal immediately behind it due to the losses it introduces.

Welded joints. Is there no Fresnel reflection on welded joints? since the cleaved ends of the fibers are fused to each other. However, there are still losses in welded joints. Is a well-welded joint difficult to detect? since the losses on it are small and the “step” that appears on the reflectogram is very small. Is the presence of even small signs of Fresnel reflection (a peak on the reflectogram) a sure sign of this? that the welded joint is of very low quality.

Bending losses. This is simply loss at the bend. If such losses are localized? then they are difficult to distinguish from losses due to welded or mechanical connections.

Increasing the sensitivity of pulsed optical reflectometers.

Measuring the parameters of a fiber-optic line is possible only if the power of the scattered signal reaching the detector exceeds the noise power, i.e. the signal-to-noise ratio must be greater than unity. The power of the detected signal is determined by the power and energy of the laser pulse introduced into the fiber and the backscattering coefficient. Let's note? that the energy of a light pulse is directly proportional to its duration. That's why? To increase the range of the reflectometer, increase the duration of the light pulses. However? The longer the pulse length, the larger the fiber segment it fills. As the pulse length increases, do those sections of the fiber also increase? which fall inside the impulse and “viewing” which becomes impossible. Does this reduce resolution? reflectometer. To increase the signal-to-noise ratio of the received signal? Does the reflectometer send many pulses? and then averages the reflected signal data.

Dead zones.

It is believed that the dead zones detected on the reflectogram depend on one main factor - the duration of the pulse passing along the fiber. Since it can be selected, each value corresponds to a specific dead zone. Therefore, the longer the pulse length, the larger the dead zone. However, once a specific pulse duration has been established (for a specific fiber), other factors become apparent. In particular, for a given pulse duration we may encounter different dead zones for reflective discontinuities depending on the distance to the reflection point and the intensity of the reflected signal. The fact is that in order to receive the reflected signal, the reflectometer detector must have high sensitivity. In this case, when a strong signal arrives at the detector (from a point with high reflectivity), the detector is overloaded. Dead zones are always associated with the presence of reflections and are caused by saturation of the reflectometer detector. In this case, the detector will require a certain time to restore sensitivity after an overload, which leads to loss of information. As a result, a certain section of the fiber is excluded from the testing process. In this case, two types of dead zones should be distinguished (Fig. 27):

1. Reflection dead zone - determined by the distance between the beginning of the reflection and the point with a level of - 1.5 dB from the top of the descending segment of the reflection curve, after which the following events are easy to identify.

2. Attenuation dead zone - determined by the distance from the beginning of the reflection to the point at which the receiver sensitivity was restored with an error of 0.5 dB from the steady-state backscatter reflectogram and depends on the pulse duration, wavelength, backscatter coefficient, reflection coefficient and bandwidth.

Thus, the concept of a “dead zone” is to quantify the distance at which data loss occurs after a strong reflection.

The attenuation dead zone is usually specified for the shortest pulses.

Rice. 26.

Rice. 27.

The best optical reflectometers are characterized by a large dynamic range, multiple determination of attenuation, a one-button interface, a simplified control panel, the presence of a display, the use of “long-range” optics with a high degree of resolution, the use of special software, are equipped with a disk drive for saving data and a printer for printing them, and also have the ability to determine OPO and compare several reflectograms. When choosing an OTDR, you should make sure that it can work with single-mode or multimode fibers. Modular optical reflectometers are more flexible and can be configured in different ways. Approximate price: $10,000-40,000.

CHROMATIC DISPERSION METER.

This instrument, as its name suggests, is designed to measure the chromatic dispersion of optical fibers. As a rule, it is made in a laboratory version for use in enclosed spaces. Various methods for measuring chromatic dispersion are described in detail in the ITU.

Approximate price, depending on the method: $25,000 - $120,000.

PMD METER.

Polarization mode dispersion of fiber light guides, like chromatic one, limits the broadband of fiber light guides. As a rule, the PMD meter is made in a laboratory version for use in enclosed spaces. Various methods for measuring PMD are described in detail in the ITU.

Approximate price, depending on the method: $40,000 - $200,000.

PERFORMANCE CONTROL SYSTEM

This computerized system is ideal for automatically managing the operation of an entire fiber optic network. All tasks: installation, routine maintenance, problem solving, repairs can be quickly tracked and controlled from a central station. Any breaks and other faults are localized within minutes with an accuracy of several meters. Approximate price: over $100,000.

Brillouin OPTICAL REFLECTOMETER.

This device measures not only Rayleigh scattering and Fresnel reflection, like an optical reflectometer, but is also capable of measuring the Mandelstam-Brillouin scattering component, shifted in frequency relative to the central wave of radiation. Able to distinguish stressed areas of the fiber and assess the degree of their load. Can also be used as a regular reflectometer. Approximate price: $200,000

An important advantage of fiber optic communication lines is their potential durability. However, to ensure long-term operation, appropriate conditions are necessary, and the main one is the absence of mechanical stresses in the fiber, which can arise in case of violation of cable production technologies, its laying, in case of frozen soil deformations, in case of wind loads and icing of the overhead cable, ground subsidence (especially near high-altitude buildings and bridges), during vibrations of cables laid near highways, during earthquakes, and other man-made interventions. Increased fiber tension in the cable causes degradation of its strength characteristics, which ultimately leads to fiber breakage. Even a slight increase in fiber tension can lead to a manifold reduction in its service life. The lifetime of the fiber under normal operating conditions (with a relative elongation of the fiber less than 0.35%) is 25 years or more, while even with a relative elongation of 0.5%, fiber rupture will occur within 1 (one)!!! year (Fig. 28).

Rice. 28

Therefore, the reliability of fiber-optic communication lines cannot be assessed without reliable information about the fiber tension in the cable. Conventional optical reflectometers are not able to determine the degree of tension in the fiber, since the amount of optical loss when stress occurs in the fiber, as a rule, remains within normal limits until irreversible changes occur in the fiber. The Brillouin reflectometer is indispensable in enterprises producing optical cables and for large telecom operators, the scale of networks and volumes of data transmission make issues of communication quality and reliability decisive.

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

Optimeters. Optimeters are divided into vertical (OBO - 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 the error of indications ±0.0002 mm, used for measuring external dimensions (gauge gauges, plug gauges and particularly precise products).

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

optimeter tubes (b)

The main reading part of the device is the optimometer tube, built according to a lever-optical design. The operating principle of the optimometer tube is shown in Fig. 23, b. Rays of light 1 guided by the mirror 2 into the slit of the tube and, refracted by a triangular prism 3 , pass through the scale printed on the plate 4 . The beam of rays then passes through a total reflection prism 5 and, reflected from it at right angles, hits the lens 6 , and then on the mirror 7 . Mirror 7 spring 8 presses against the measuring rod 9 , and when the measuring rod moves, the mirror rotates around an axis passing through the center of the ball 10 . The angle of rotation of the mirror depends on the inclination of the mirror 7 . In Fig. 23, b shows the path of one incident ray (solid line) and reflected ray (dashed - dotted line). The angle between these rays is equal to 2 .

The reflected beam of rays is transformed by the lens into a converging beam of rays, which gives an image of the scale. Installing the instrument tube along the gauge block involves aligning the zero line 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 stationary pointer.

Measuring spring-optical heads. These devices have an abbreviated name - opticators. They use the spring principle of a microcator, only it is not an arrow that is attached to a curled spiral spring, but a mirror onto which a beam of light falls and is reflected onto a glass scale, where an image of an index line appears. The produced spring-optical heads, designated OP, have a connecting diameter 28 mm and are designed for precise linear measurements when securing heavy mud in racks. The measuring heads have a rotating scale for precise adjustment to the size and tolerance field indicators in the form of colored curtains in the path of the light beam (bunny) coloring it green or red. Spring-optical heads are available in dolemicron (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 air flowing with 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 µm). This calibration makes it possible to directly count deviations in the dimensions of the parts being tested from the size of the reference part or measure by which the device is configured and to determine deviations from the correct geometric shape of the products. Factories use two types of devices: low pressure devices based on changes in air pressure ( rice. 24,a), and float meters (rotameters), based on changes in air flow ( rice. 24, b).

Rice. 24. Pneumatic length gauges:

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

c – plug in the hole (section)

Low pressure devices are available with two or more scales for simultaneous or separate measurement of two or more sizes. On 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. Measurement limits can be changed from 0,02 before 0.20 mm, since they depend on the size of the nozzles used in the device. At measurement limit 0.02 mm the maximum error of readings is 0.0005 mm, and at the largest measurement limit 0.20 mm the error is correspondingly equal 0.005 mm.

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

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

Before measuring the diameters of the holes using a pneumatic device, a specially designed plug is inserted into the reference ring and, by adjusting the air supply using screw 5, the float 3 in tube 2 is set to the zero position. If the hole size of the part being tested 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 being tested 90, 180 And 270° in the same and different sections along the axis of the part, it is possible to determine the deviations of parts from the correct geometric shape.

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

Calibers

During mass production of products, when the factory is forced to measure parts to the same size every day, rigid construction tools are widely used - limit gauges (Fig. 25): plugs for checking holes ( rice. 25,a,b) and brackets for checking shafts ( rice. 25,c,d). The gauges do not have reading devices for determining dimensions; with their help, you can only determine whether the actual size of the part is within the tolerance or not. For this purpose, gauges are made according to the maximum dimensions of the part being tested. One side of the plug (elongated) will have a nominal size and is called the bore hole, 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-passing and is designated NOT; it can only fit into a part that has an oversized hole. Such parts are rejected.

The process of checking parts consists of simply sorting them using two limiting gauges into three groups: suitable parts, the size of which is within the permissible limits (PR passes; and does NOT pass); The defect is correctable when the shaft size is larger than the permissible size, and the hole size is less than the permissible one (PR does not pass); The defect is irreparable when the size of the shaft is underestimated and the size of the hole is too high (does NOT pass).

The gauges used by workers and quality control inspectors to check parts are called working gauges; their types, sizes and technical specifications are standardized.

Rice. 25. Calibers.

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

g – limit adjustable bracket

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

Gauge gauges for shafts most often use single-sided limit whole or double-sided sheet ( rice. 25,v). For shaft sizes from 100 before 360 mm use one-sided limit brackets with insert jaws ( rice. 25, g). The following designations (markings) 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 (quality), digital values ​​of the maximum deviations of the part in millimeters, the designation of the sides of the gauge - pass PR and non-pass NOT, trademark of the manufacturer. For go-through gauges, the standards provide manufacturing and wear tolerances, while for non-go gauges there are only manufacturing tolerances. Standard deviations for the manufacture and wear of gauges are measured from the maximum dimensions of shafts and holes; for pass-through brackets - from the largest maximum shaft size, and for pass-through plugs - from the smallest maximum hole size; for non-go gauges, 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 a special procedure for determining the maximum (executive) dimensions of pass gauges, Z And Z 1– these are deviations from the middle of the tolerance field for the production of pass-through gauges ( Z for the hole and Z 1 for a shaft) relative to the smallest hole size and the largest maximum shaft size; N And H 1– tolerances for the manufacture of go-through and no-go gauges (for a hole N and shaft H 1); Y And Y 1– permissible exits of a worn caliber beyond the tolerance zone (holes Y and shaft Y 1).

For calibers with dimensions greater than 180 mm, additional values ​​for caliper control error compensation are provided, indicated for holes and for the shaft.