Measurement technique. Types, methods and measuring instruments. Physical quantities. Measurement of physical quantities. Accuracy and measurement error Methodology for measuring physical quantities
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Twitter.Measurement methods are determined by the type of measured values, their dimensions required by the accuracy of the result required by the speed of the measurement process and other data.
There are many methods of measurement, and as science and technology develops and the number of them increases everything.
By a method for producing a numerical value of the measured value, all measurements are divided into three main types: direct, indirect and cumulative.
Straightthey are called measurements in which the desired value of the magnitude is directly from the experimental data (for example, the measurement of the mass on the dial or equal departure weights, the temperature is a thermometer, lengths - with linear measures).
Indirect measurements are called at which the desired value is found on the basis of the known relationship between this magnitude and values \u200b\u200bsubjected to direct measurements (for example, the density of a homogeneous body by weight and geometric sizes; determination of electrical resistance according to the results of measuring the voltage drop and current).
Cumulative measurements are called at the same time, several of the same names are measured simultaneously, and the desired value of the values \u200b\u200bare found by the solution of the system of equations obtained by direct measurements of various combinations of these values \u200b\u200b(for example, measurements in which the mass of individual dialing weights are installed according to the known mass of one of them and according to the results of direct Compare masses of various combinations of Giri).
Earlier it was said that in practice, direct measurements were most common due to their simplicity and velocity. We give a brief description of direct measurements.
Direct measurements of values \u200b\u200bcan be performed by the following methods:
1) Direct Assessment Method - The value of the value is determined directly via the verification device of the measuring instrument (measurement of pressure - spring pressure gauge, mass - dial weights, electric current forces - ammeter).
2) Comparison method with measure – the measured value is compared with the value of the reproducible measure (measurement of the mass by lever weights with balancing weights).
3) Differential method - The comparison method with a measure in which the difference between the measured value and the known value is valid for the measuring device, which is reproduced by measure (measurements performed when checking the length of the length of the sample measure on the comparator).
4) Zero method - Comparison method with measure when the resulting effect of exposure values \u200b\u200bon the comparison device is adjusted to zero (measuring the electrical resistance by the bridge with its full balancing).
5) Method of coincidence - The comparison method with a measure, in which the difference between the measured value and the value of the reproducible measure is measured using the coincidence of the scales or periodic signals (measurement of length using a nonius caliper, when there are matching marks on the calipers and noniural scales).
6) Method of substitution – the comparison method with a measure when the measured value is replaced by a known value reproducible to the measure (weighing with an alternate room of the measured mass and the weight of the same scales).
End of work -
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Metrology
The concept of metrology as a science metrology Science of measurements of methods and .. Basic concepts related to measurement objects ..
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All the themes of this section:
The concept of metrology as a science
Metrology - science of measurements, methods and means of ensuring their unity and how to achieve the required accuracy. In a practical life man Sun
Concept of measurement tools
Measurement (SI) - this is a technical means (or a complex of technical means) intended for measurement having normalized metrological character
Metrological characteristics of measuring instruments
Metrological characteristics of measuring instruments are characteristics of properties that influence the results and error of measurements. Meter Appointment Information
Factors affecting measurement results
In metrological practice, when measuring, it is necessary to take into account a number of factors affecting the measurement results. This is an object and subject of measurement, measurement method, Wed
Formation of measurement results. Measurement errors
The measurement procedure consists of the following main stages: 1) adopting the model of objects; 2) the choice of the measurement method; 3) the choice of measuring instruments;
Presentation of measurement results
There is a rule: the measurement results are rounded up to the "error". In practical metrology, rules for rounding results and measurement errors have been developed. OS.
Causes of measurement errors
There are a number of components of the errors that are dominant in the overall measurement error. These include: 1) errors, dependent measurement tools. But
Processing multiple measurements
We assume that measurements are equicious, i.e. Performed by one experimenter, in the same conditions, by one device. The technique is reduced to the following: n observations are carried out (one
Student's distribution (T-criterion)
N / α 0.40 0.25 0.05 0.05 0.025 0.01 0.005 0.0005
Methods of measurement measurements
The main loss of accuracy in measurement occurs due to the possible metrological malfunction of the used measuring instruments, and primarily due to imperfection method
The concept of metrological support
Under metrological support (MO) means the establishment and application of scientific and organizational foundations, technical means, rules and norms,
Systematic approach in the development of metrological support
When developing MO, it is necessary to use a systematic approach, the essence of which consistent with MO as a set of interrelated processes, united by one goal - achieved
Basics of metrological support
Metrological support has four bases: scientific, organizational, regulatory and technical. Their content is shown in Figure 1. Separate aspects of MO considered in the river
Legislation of the Russian Federation on ensuring the unity of measurements
The regulatory framework for the unity of measurements is presented in Figure 2.
National system for ensuring unity of measurements
The national system for ensuring unity of measurements (NSOEY) is a set of rules for performing work on ensuring the unity of measurements, its participants and rules
Main types of metrological activities to ensure the unity of measurements
Under the unity of measurements is understood as a state of measurements, in which their results are expressed in legalized units of magnitudes and errors (vague
Assessment of Measurement Measurement
During the measurements relating to the field of state regulation of ensuring the unity of measurements, SI must be applied in Russia.
Approval of the type of measuring instruments
Approval of the type (except Sausch) is carried out on the basis of positive test results. Approval of the type of sucks is carried out on the basis of the positive results of Atte
Certification of measurement methods
Methods for performing measurements is a set of operations and rules, the execution of which ensures the result of the measurement result with the established error.
Verification and calibration of measuring instruments
Verification of measuring instruments are a combination of operations performed in order to confirm the compliance of the actual values \u200b\u200bof metrological characteristics.
Structure and functions of the metrological service of the enterprise, organization, institutions that are legal entities
Metrological service of the enterprise, organization and institutions that use the rights of a legal entity, regardless of the forms of ownership (hereinafter - enterprises) includes a department (service)
The concept of interchangeability
Interchangeability is called the property of the same parts, nodes or machine aggregates, etc., which allows you to install parts (nodes, units) in the process of assembly or deputy
Qualites, basic deviations, landing
The accuracy of the part is determined by the accuracy of the size, roughness of the surfaces, the accuracy of the shape of the surfaces, the accuracy of the location and the waviness of the surfaces. For secure
Designation of fields for tolerances, limit deviations and landings in the drawings
The limit deviations of linear dimensions indicate the drawings with conditional (lettering) designations of tolerance fields or numerical values \u200b\u200bof limit deviations, as well as lettering
Unspecified limit deviations of sizes
The limit deviations not specified immediately after the nominal sizes, but specified by the overall record in the technical requirements of the drawing, are called unspecified limit deviations.
Recommendations for the use of landing with a gap
Landing H5 / H4 (SMIN \u003d 0 and SMAX \u003d TD + TD) are prescribed for pairs with accurate centering and direction in which turning and longitudinal movement is allowed
Recommendations for the use of transitional landings
Transitional landings H / js, n / k, n / m, n / n are used in fixed details for centering replaceable parts or parts, which can be moved by VD if necessary.
Recommendations for the use of landings with tension
Landing n / r; P / H - "Legging" - are characterized by minimal guaranteed tension. Installed in the most accurate qualifications (shafts 4 - 6th, openings 5 \u200b\u200b- 7-
Concept of surface roughness
The roughness of the surface according to the GOST 25142 - 82 is a combination of surface irregularities with relatively small steps allocated by base length. Basic
Roughness parameters
According to GOST 2789 - 73, the roughness of the surface of the products, regardless of the material and method of manufacture, can be evaluated by the following parameters (Figure 10):
General Terms and Definitions
Tolerances forms and location of the surfaces of parts of machines and instruments, terms, definitions related to the main types of deviations, standardized GOST 24642 \u200b\u200b- 81. Based on
Deviations and tolerances
Deviations of form include deviations of straightness, flatness, roundness, longitudinal and cylindrical profile. Deviations of flat surface
Deviations and tolerances
The deviation of the surface or profile is called the deviation of the real location of the surface (profile) from its nominal location. Quantify the location of
Total deviations and tolerances forms and location of surfaces
The total deviation of the shape and arrangement is the deviation, which is the result of the joint manifestation of the deviation of the shape and deviation of the location of the element under consideration (
Dependent and independent shape tolerance and location
Tolerances or shapes installed for shafts or holes may be dependent and independent. The permissible tolerance of the form or location is dependent, the minimum is
Numerical values \u200b\u200bof form tolerances and location of surfaces
According to GOST 24643 - 81, for each type of tolerance of the shape and the location of the surfaces, 16 degrees of accuracy is established. Numerical values \u200b\u200bof tolerances from one degree to another are changed
Designation on form and location tolerances
The type of tolerance of the form and location according to GOST 2.308 - 79 should be denoted on the drawing signs (graphics symbols) shown in Table 4. The sign and numeric tolerance value fit
Unspeakable tolerances of form and location
Directly in the drawing indicate, as a rule, the most responsible tolerances forms and location of surfaces. According to GOST 25069 - 81, all indicators of the accuracy of the form and
Rules for determining the base
1) If the item has more than two elements for which the unrepared tolerances or beats are installed, then these tolerances should be attributed to the same database;
Rules for determining the decisive size
Under the defining size allowance is meant: 1) when determining unspecified admission of perpendicularity or oversized beating - size admission coordinating
Wavy surface
Under the waviness of the surface, there is a combination of periodically repeated irregularities, in which the distances between adjacent hills or depressions exceed the base length L.
Rolling bearings tolerances
The quality of bearings will be determined by: 1) the accuracy of the connecting dimensions and the width of the rings, and for roller radially resistant bearings E
Selection of rolling bearings
Landing rolling bearing on the shaft and in the case are selected depending on the type and size of the bearing, the conditions of its operation, the values \u200b\u200band the nature of the loads acting on it and the type of loading of the rings
Decision
1) with a rotating shaft and the permanent effect of FR, the inner ring is loaded circulating, and the outer-local loads. 2) load intensity
Legend bearings
System of conditional designations of ball and roller bearings is installed GOST 3189 - 89. The conventional bearing designation gives a complete picture of its overall sizes, designs, accuracy
Tolerances of angular sizes
Angle size tolerances are prescribed according to GOST 8908 - 81. AT angles tolerances (from English. Angle Tolerance - angle tolerance) must be assigned depending on the nominal length L1 of the smaller side
System of tolerances and landings for conical compounds
The conical compound compared with cylindrical has advantages: you can adjust the size of the gap or the tightness by the relative displacement of parts along the axis; With a fixed compound
Main parameters of metric mounting thread
Cylindrical thread parameters (Figure 36, a): Medium D2 (D2); Outdoor D (D) and internal D1 (D1) diameters on
General principles of interchangeability of cylindrical threads
Systems of tolerances and landings that provide interchangeability of metric, trapezoidal, stubborn, tubular and other cylindrical threads, built on a single principle: they take into account the availability of
Tolerances and landing threads with gap
Tolerances for metric threads with large and small steps for diameters 1 - 600 mm are regulated by GOST 16093 - 81. This standard sets the limit deviations of the thread diameters in
Tolerances with tension and adapted landings
The landings under consideration serve mainly for connecting studs with body parts, if you cannot apply the screw or type bolt connections. These landings are used in the mounting connections.
Standard Common and Special Threads
Table 9 shows the names of standard threads of general purpose, the most widespread in the machine and instrument making, and are given examples of their designation in the drawings. To the most
Kinematic transmission accuracy
To ensure kinematic accuracy, norms limiting the kinematic transmission error and the kinematic error of the wheel are provided. Kinematic
Smoothness of the transfer
This transmission characteristic is determined by the parameters whose errors are repeated (cyclically) manifest themselves for the turnover of the gear wheel and also constitute part of the kinematic
Contact teeth in transmission
To increase the wear resistance and durability of gear, it is necessary that completeness of the contact of the conjugate side surfaces of the wheels of the wheels was the greatest. In case of incomplete and
Side clearance
To eliminate a possible jamming when the transmission is heated, ensuring the conditions for the flow of lubricant material and the limitations of the dead turn when reversing the counting and dividing real reversal
Designation of wheel and gear accuracy
The accuracy of the manufacture of gear wheels and gears set the degree of accuracy, and the requirements for the side gap - a view of the pairing on the norms of the side gap. Examples of conditional notation:
Choose the degree of accuracy and controlled gearbox parameters
The degree of precision of the wheels and gears is established depending on the requirements for kinematic accuracy, the smoothness transmitted by the power, as well as the circumferential velocity of the wheels. When choosing the degree of accuracy
Tolerances of gem conical and hypoid gears
Principles of constructing an admission system for gear conical (GOST 1758 - 81) and hypoid gear (GOST 9368 - 81) are similar to the principles of building a system for cylindrical transmissions
Worm-cylindrical tolerances
For worm cylindrical transmissions GOST 3675 - 81 sets 12 precision degrees: 1, 2 ,. . ., 12 (in descending order of accuracy). For worms, worm wheels and worm gears
Tolerances and landing of connections with a straight profile of teeth
According to GOST 1139 - 80, the tolerances are installed for compounds with internal D and outer D diameters, as well as on the side sides of the teeth b. Since the view of Centrirova
Tolerances and landing of slotted compounds with the eusolvent profile of teeth
Nominal sizes of slotted compounds with an eusolvent profile (Figure 58), nominal sizes on the rollers (Figure 59) and the length of the total normal for individual measurements of the slotted shafts and sleeves must
Control accuracy of slot compounds
Split compounds are controlled by complex passing gauges (Figure 61) and elementary non-return calibers.
The method of calculating the dimension chain, providing full interchangeability
To ensure complete interchangeability, the dimensional chains are calculated by a maximum minimum method, in which the tolerance of the closing size is determined by the arithmetic addition of tolerances
Theoretical and probabilistic method for calculating dimensional chains
When calculating the dimensional circuits by the maximum method, the minimum was assumed that in the processing or assembly process, the simultaneous combination of the largest increasing and least reduction of
Method of group interchangeability in selective assembly
The essence of the group interchangeability method is to manufacture parts with relatively wide technologically executable tolerances selected from the corresponding standards, grade
Method of regulation and fit
Admission method. Under the method of regulation, the calculation of the size chains is understood, in which the required accuracy of the initial (closing) link is achieved by deliberate change
Calculation of flat and spatial dimensional chains
Flat and spatial dimensional chains are calculated by the same methods as linear. It is only necessary to lead them to the type of linear dimension chains. This is achieved by projection
Historical basics of standardization development
The standardization is man engaged in ancient times. For example, writing has at least 6 thousand years and arose according to the last finds in Sumer or Egypt.
Legal bases of standardization
The legal framework for standardization in the Russian Federation establishes the Federal Law "On Technical Regulation" of December 27, 2002. He is obligatory for all state-owned
Principles of technical regulation
Currently, the following principles are established: 1) the use of uniform rules for establishing products to products or to related design processes (including surveys)
Objectives of technical regulations
Technical Regulation Act establishes a new document - technical regulations. Technical Regulations - a document that is adopted by the International Treaty of Russia
Types of technical regulations
In the Russian Federation, two types of technical regulations are applied: - General technical regulations; - Special technical regulations. General technical regulations
Concept of standardization
The content of standardization terms has passed a long evolutionary path. The clarification of this term occurred in parallel with the development of the standardization itself and reflected the achieved level of its development on P
Objectives of standardization
Standardization is carried out in order to: 1) improve the level of security: - the life and health of citizens; - property of individuals and legal entities; - state
Object, aspect and standardization area. Standardization levels
The object of standardization is a specific product, services, production process (work), or groups of homogeneous products, services, processes for which the requirements are developing
Principles and Standardization Functions
The basic principles of standardization in the Russian Federation, ensuring the achievement of the goals and objectives of its development, are to: 1) the voluntary application of documents in the field of standardization
International Standardization
International standardization (MS) is an activity in which two or more sovereign states participate. MS owns a prominent role in the deepening of world economic cooperation, in m
Complex standards of the national standardization system
For the implementation of the Federal Law "On Technical Regulation" since 2005, there are 9 national standards for the "Standardization of the Russian Federation", which replaced the Complex "State Standardization system". it
Structure structure and standardization services
The National Standardization Authority is the Federal Agency for Technical Regulation and Metrology (Rostechregulation), it replaced GOSSTANDAT. It obeys directly
Standardization Regulatory Documents
Regulatory documents on standardization (ND) - Documents containing rules, general principles for the standardization object and are available to a wide range of users. The ND refers: 1)
Standards categories. Standards designations
Categories of standardization are distinguished by what level standards are accepted and approved. Four categories are installed: 1) international; 2) intergovernmental
Types of standards
Depending on the object and aspect of standardization, GOST P 1.0 establishes the following types of standards: 1) the standards are fundamental; 2) standards for products;
State control over compliance with the requirements of technical regulations and standards
State control is carried out by officials of the State Control Body of the Russian Federation for compliance with the requirements of the TRP of product circulation. State control bodies
Standards of organizations (service station)
The organization and procedure for developing a hundred is contained in GOST R 1.4 - 2004. The organization is a group of workers and the necessary funds with the distribution of responsibility of authority and
The need for preferred numbers (PC)
The introduction of the PC is caused by the following considerations. The use of PC makes it possible to best carry out the parameters and sizes of a separate product with all associated with them.
Rows based on arithmetic progression
Most often, the rows of PC are built on the basis of geometric progression, less often on the basis of arithmetic progression. In addition, there are varieties of ranks built on the basis of "Gold &
Rows based on geometric progression
Long-term standardization practice has shown that rows built on the basis of geometric progression are most convenient because it turns out the same relative difference between
Properties of series of preferred numbers
The ranks of the PC have the properties of geometric progression. The rows of the PC are not limited in both directions, the numbers less than 1.0 and more than 10 are obtained by division or multiplication by 10, 100, etc.
Limited, selective, composite and approximate rows
Limited rows. If it is necessary to limit the main and additional rows in their designations, limit members are indicated, which are always included in limited rows. Example. R10 (
Concept and types of unification
During the unification, the minimum allowable, but sufficient number of types, species, sizes, products, assembly units and parts with high quality indicators
Unification level indicators
Under the level of unification of products it is understood as the saturation of their unified components; Details, modules, nodes. The main quantitative indicators of the level of unification
Determination of the level of unification
Evaluation of the level of unification is based on the correction of the following formula:
Certification Development History
"Certificate" in translation from Latin means "done right". Although the term "certification" became known in everyday life and commercial practice
Terms and definitions in conformation
Compliance assessment is a direct or indirect definition of compliance with the requirements for the object. A typical example of assessing activities
Objectives, principles and confirmation objects
Conformity confirmation is carried out in order to: - certificates of product conformity, design processes (including research), production, construction, installation
The role of certification in improving product quality
A fundamental improvement in product quality in modern conditions is one of the key economic and political tasks. That is why the combination of such a decision is directed
Product certification schemes for compliance with technical regulations
Certification scheme - a certain set of actions, officially adopted as evidence of compliance with the specified requirements.
Conformation Declaration Schemes for Compliance with Technical Regulations
Table 17 - Declaration schemes for compliance with the requirements of technical regulations Designation of the scheme The content of the scheme and its
Services certification schemes
Table 18 - Certification Schemes Schemes Schemes Evaluation of the quality of the provision of services Check (testing) service results
Confirmation Confirmation Schemes
Table 19 - Production Certification Schemes The number of the test scheme in accredited test laboratories and other ways of proof
Mandatory confirmation of conformity
Mandatory confirmation of compliance can be carried out only in cases established by technical regulations and solely for compliance with their requirements. Wherein
Declaration of conformity
In the Federal Law "On Technical Regulation", the conditions are formulated, subject to the compliance with the Declaration on Compliance. First of all, this form of confirmation of conformity
Mandatory certification
Mandatory certification in accordance with the Federal Law "On Technical Regulation" is carried out by an accredited certification authority on the basis of an agreement with the applicant.
Voluntary confirmation of conformity
Voluntary confirmation of conformity should be carried out only in the form of voluntary certification. Voluntary certification is carried out at the initiative of the applicant on the basis of the DOO
Certification systems
Under the certification system means a combination of certification participants acting in a specific area according to the rules defined in the system. The concept of "certification system" in
Certification procedure
Product certification takes place in the following basic stages: 1) Applying for certification; 2) consideration and decision-making on request; 3) Selection, ID
Certification bodies
The certification authority is a legal entity or an individual entrepreneur accredited in the prescribed manner to perform certification work.
Test laboratories
Testing laboratory - a laboratory that conducts tests (separate types of tests) of certain products. When carrying out Ser.
Accreditation of certification organs and test laboratories
According to the definition given in the Federal Law "On Technical Regulation", accreditation is "official recognition by the accreditation authority of the competence of physical
Certification of services
Certification is carried out accredited authorities for certification services within their area of \u200b\u200baccreditation. When certified, the characteristics of the services are checked and the methods are used.
Certification of quality systems
In recent years, the number of companies that certify their quality systems for compliance with ISO series 9000 are rapidly growing in the world. These standards are currently used.
Measure- This is the foundation of the physical value by experimenting with the help of special technical means. Measurements are classified by: ♦ a method for obtaining information; ♦ the character of changes in size in the process of its measurements; ♦ the number of measuring information; ♦ Relationship to basic units of measurement. According to the method of obtaining measurement information, divided into direct indirect, cumulative and joint. By the nature of the changes of the measured value during the measurement processallocate statistical, dynamic and static measurements.
By the number of measuring informationdistinguish between single and multiple measurements. relationship to major units of measurementallocate absolute and relative measurements.
The principle of measurements -the physical phenomenon or effect based on measurements (for example, the use of the Doppler effect for measuring the speed is occurring with any wave energy propagation process; use of gravity when weighing mass changes).
Measurement method -this method or a set of comparison methods of the measured physical value with its unit in accordance with the implemented measurement principle (measurement method is usually due to the measurement tool device)
The following measurement methods are distinguished: methods of direct measurement estimation (the value of the value is determined directly on the indicative of the measurement means); . ♦ Comparison methods with measure (measured values \u200b\u200bare compared with the values \u200b\u200bthat reproduce the measure); ♦ zero measurement method (the resulting effect of the measured value and measure on the comparison device is adjusted to zero); ♦ the measurement method of the substitution (the measured value is replaced by measure with a known value of the value); ♦ Measurement method with an addition (the value of the measured value is complemented by the measure of the same value with In such a calculation, in order for the comparison device to be affected by their amount equal to the advanced value); ♦ Differential measurement method (the measured value is compared with a homogeneous value having a known value, slightly different from the value of the measured value when the difference between these two values \u200b\u200bis measured); ♦ Contact measurement method (measuring the diameter of the shaft with a measuring bracket or passing and non-passing caliber); ♦ The non-contact measurement method (the measurement tool element is not brought to contact with the measurement object (for example, temperature measurement in the furnace). Methods of performing measurements- This is the established set of operations and rules when measuring.
Physical values \u200b\u200bas measurement objectsThe physical value is one of the properties of the physical object, in common with a qualitative relation for many physical objects, but individual in a quantitative relation for each of them. Measured physical quantityit is a quantitative physical quantity to be measured, measured or measured in accordance with the main purpose of the measuring task. System of units of physical quantities- This is a combination of basic and derivative physical quantities formed in accordance with the principles accepted when some values \u200b\u200bare made for independent, while others are their functions. Mainthe physical quantity is called in the system of magnitude and conditionally adopted as independent of other values \u200b\u200bof this system. Derivativethe physical quantity is called the system and determined through the main values \u200b\u200bof this system.
The main values \u200b\u200bare independent of each other, but they can serve as a basis for establishing links with other physical quantities, which are called derivatives from them. For example, in the Einstein formula, the main unit includes a mass and derivative unit - energy. The main values \u200b\u200bcorrespond to the basic units of measurements, and derivatives - derivatives. The physical value has a certain dimension -the expression in the form of a powerful single-sized, composed of the works of the symbols of the main physical quantities in various degrees, reflecting the relationship of this physical quantity with physical quantities adopted in this system for basic, and with a proportionality coefficient equal to one.
22. Measuring temperature.There are two main methods for measuring temperatures - contact and non-contact. Contact methods are based on the direct contact of the temperature transducer with the object under study, as a result of which the state of thermal equilibrium of the converter and the object is achieved. This method is inherent in its drawbacks. The temperature field of the object is distorted when the therm acceptor is introduced into it. The temperature of the converter is always different from the true temperature of the object. The upper limit of temperature measurement is limited by the properties of materials from which temperature sensors are made. In addition, a number of temperature measurement tasks in inaccessible rotating at high speed facilities cannot be resolved with contact method.
The contactless method is based on the perception of heat energy transmitted through radiating and perceived at some distance from the studied volume. This method is less sensitive than contact. Temperature measurements are largely dependent on reproduction of conditions of graduation during operation, and otherwise significant errors appear. A device that serves to measure the temperature by converting its values \u200b\u200binto a signal or indication is called a thermometer (GOST 13417-76),
According to the principle of action, all thermometers are divided into the following groups that are used for different temperature ranges: 1 expansion thermometers from --260 to +700 ° C, based on changing the volume of liquids or solids when the temperature changes. 2 Manometer thermometers from - 200 to +600 ° C, measuring the temperature of fluid pressure, steam or gas in a closed volume from temperature change.3. Electrical resistance thermometers are standard from --270 to +750 ° C, transforming a change in temperature to change the electrical resistance of conductors or semiconductors. 4. Thermoelectric thermometers (or pyrometers), standard from --50 to +1800 ° C, based on the conversion of which lies the dependence of the value of the electromotive force from the temperature of the discharge of heterogeneous conductors.
Radiation Pyrometers from 500 to 100000 ° C, based on temperature measurement of the intensity of radiant energy emitted by heated body, thermometers based on electrophysical phenomena from -272 to +1000 ° C (thermoshumium thermoelectric transducers, volumetric resonant thermal converters, nuclear resonance).
Slide 2.
Metrology- the science about measurements, methods to achieve their unity and required accuracy. Measurements play an important role in human life. With measurements, we meet at every step of our activities, ranging from the determination of the distances to the eye and ending with the control of complex technological processes and the implementation of scientific research. The development of science is inextricably linked with progress in the field of measurements.
Slide 3.
As a field of practical activity, metrology originated in antiquity. The name of the measurement units and their dimensions appeared in ancient times most often in accordance with the possibility of applying units and their size without special devices. The first measurement tools were objects based on the size of the hands and feet of the person. In Russia, the elbow was used, span, sootten, mowy sage. In the West - inch, foot, who has retained its name so far. Since the dimensions of the arms and legs in different people were different, then the proper unity of measurements was not always able to provide. The next step was the legislative acts of the rulers, prescribing, for example, per unit of length count the average length of the foot of several people. Sometimes the rulers simply made two knots on the wall of the market square, prescribing all merchants to make copies of such "reference measures.
In early 1840, the standard of meters was installed in France (the standard is stored in France, in the museum of measures and weights; currently is more historical exhibit, rather than a scientific instrument);
A big role in the formation of metrology in Russia was played by D.I. Mendeleev, who led by the domestic metrology in the period from 1892 to 1907, "Science begins ... Since they begin to measure," in this scientific sense of the great scientist is expressed, essentially, the most important principle of the development of science, which has not lost the relevance and in modern conditions.
On his initiative, the St. Petersburg Academy of Sciences proposed to establish an international organization that would ensure the uniformity of measuring instruments internationally. This proposal was approved, and on May 20, 1875 at the diplomatic metrological conference held in Paris, in which 17 states participated (including Russia), was adopted Metric Convention.
World Metrology Day is celebrated annually on May 20. The holiday was established by the International Committee of Measures and Scales (ICMV) in October 1999, at 88 meeting of the ICMV.
Slide 4 object and subject of metrology
Metrology (from Greek. "Metron" - Measure, "Logos" - doctrine) is a science of measurements, methods and means of ensuring the unity of measurements and methods and means of ensuring their required accuracy.
Any science is held if it has its own object, subject and research methods. The subject of any science answers the question that it is being studied.
The subject of metrology is to measure the properties of objects (length, mass, density, etc.) and processes (the rate of flow, the intensity of the flow, etc.) with a given accuracy and reliability.
The object of metrology is a physical amount
Slide 5.
Objectives and objectives of metrology:
· Education of units of physical quantities and systems of units;
· Development and standardization of methods and means of measurements, methods for determining the accuracy of measurements, the basics of ensuring the unity of measurements and uniformity of measurement tools (the so-called "Legislative Metrology");
· Creation of standards and exemplary measuring instruments, verification of measures and measuring instruments. The priority subtask of this area is the development of a system of standards based on physical constants.
The most important task of metrology is to ensure the unity of measurements.
Slide 6.
Metrology is divided into three main sections: "Theoretical Metrology", "Applied (Practical) Metrology" and "Legal Metrology".
Slide 7.
Theoretical metrology
Considers general theoretical problems (the development of theory and problems of measurement of physical quantities, their units, measurement methods).
Slide 8.
Applied
Learns issues of practical application of the development of theoretical metrology. In its jurisdiction there are all issues of metrological support.
Slide 9.
Legislature
It establishes mandatory technical and legal requirements for the use of units of physical quantity, methods and measuring instruments.
Slide 10, 11, 12, 13
We write down the basic concepts of metrology:
· Unity of measurements - The state of measurements characterized by the fact that their results are expressed in legal units, the dimensions of which are equal to the size of units reproduced by primary standards, and the errors of measurement results are known and the specified probability does not go beyond the established limits.
· Physical quantity - One of the properties of the physical object, in common with quality for many physical objects, but in quantitatively individual for each of them.
· Measure - A combination of operations on the use of a technical means storing a unit of physical quantity, ensuring the detection of the ratio of the measured value with its unit and obtaining the value of this magnitude.
· Measurement means - Technical means intended for measurements and having normalized metrological characteristics.
· Verification - A combination of operations performed in order to confirm the conformity of measuring instruments in metrological requirements.
· Measurement error - deviation of the measurement result from the true value of the measured value.
· Measurement error - The difference between the indication of the measurement tool and the valid value of the measured physical quantity.
· Accuracy Measurement Means - Characteristics of quality Measurement Means, reflecting the proximity of its error to zero.
· License - This is a permit issued by the state metrological service authorities on the territory enshrined after it, the physical or legal entity for the implementation of activities for the production and repair of measuring instruments.
· Measure - This is a measurement tool intended for playing F.V. specified size.
· Etalon units of magnitude - Technical means intended for transferring, storing and playing a unit of magnitude.
Slide 14.
The physical quantity is one of the properties of the physical object, in common with a qualitative attitude for many physical objects, but in quantitatively individual for each physical object.
Physical quantities are divided into measurable and evaluated.
Measured physical quantities can be quantified in the established units of measurement (units of physical quantity).
The estimated physical quantities are values \u200b\u200bfor which units of measurements cannot be entered. They are determined using the installed scales.
Slide 15.
Physical quantities are classified according to the following types of phenomena:
a) real - they describe the physical and physico-chemical properties of substances, materials and products of them;
b) energy - describe the energy characteristics of processes
transformations, transmission and absorption (use) of energy;
c) physical quantities characterizing the flow of processes in time.
Slide 16.
The unity of physical quantity is called the physical amount of fixed size, which is conditionally assigned a numerical value equal to one, and which is used for the quantitative expression of homogeneous physical quantities.
There are basic and derivative units of physical quantities. For some physical values, units are set arbitrarily, such units of physical quantities are called the main. Derivative units of physical quantities are obtained by formulas from the main units of physical quantities.
The system of units of physical quantities is a combination of basic and derivative units of physical quantities relating to a certain system of quantities.
Thus, in the International System System (International System), seven basic units of physical quantities were adopted: a time unit - second (C), a unit of length - meter (m), mass - kilogram (kg), unit of power of electric current - amp (a) , thermodynamic temperature - Kelvin (K), the forces of light - candela (CD) and a unit of the amount of matter - mole (mol).
Slide 17.
Measuring physical quantities
Measurement is the foundation of the physical value by experimental through special technical means.
The true value of the physical value is a value that perfectly reflects the corresponding property of the object, both in a quantitative and qualitative relationship.
The actual value of the physical value is the value found by the experienced way and so close to the true one that this goal can be accepted instead of it.
The measured value of the physical quantity is the value obtained by measuring using specific methods and measuring instruments.
Measurement properties:
a) accuracy is a measurement property that reflects the proximity of their results to the true value of the measured value;
b) correctness is a measurement property that reflects the proximity to zero systematic errors in their results. The measurement results are correct when they are not distorted by systematic errors;
c) Convergence is a measurement property that reflects the proximity to each other the results of measurements performed at the same conditions with the same measurement means with the same operator. Convergence - important quality for measurement methods;
d) Reproducibility is a measurement property that reflects the proximity to each other of the results of measurements performed in different conditions, i.e, at different times, in different places, different methods and measurement means. Reproducibility - Important quality when testing finished products.
Slide 18, 19, 20
Classification of measurements
Measurements are classified according to the following features:
1 on the physical essence of the measured value
2 by accuracy characteristic
A) Equal measurements are a series of measurements of any physical quantity of the measurement facility under the same conditions (the same measurement means, the parameters of the medium, the same operator, etc.)
B) The unequal measurements are a series of measurements of any physical quantity made either by different accuracy devices or under different measurement conditions.
3 in terms of measurements
A) single measurements
B) multiple measurements - measurements of the same physical value resulting from several measurements in each other.
4 by changing the measured value in time
A) static
B) dynamic (in which the measured value varies in time)
5 in metrological purpose
A) technical
B) metrological
6 to express measurement results
A) absolute - measured in kg., M., N, etc.
B) Relative - measured in fractions or percentages.
7 According to the method of obtaining a numerical value of the physical quantity
A) straight - these are measurements in which the desired value of physical quantity is obtained directly.
B) indirect - these are measurements in which the desired value of physical quantity is obtained on the basis of direct measurements of other physical quantities.
C) Joint measurements are the simultaneous measurement of two or more non-encoded FV to determine the relationship between them.
D) Cumulative is the simultaneous measurement of several of the same names of physical quantities, and the desired value of quantities are found by solving the system of equations obtained with direct measurements of various combinations of these values.
Slide 21.
Methods for measuring physical quantities
The measurement method is the reception or a set of receptions of the comparison of the measured physical quantity with its unit in accordance with the realized principle of measurements.
Factors affecting measurement results
Network practices during measurements need to take into account a number of factors affecting the measurement results. This is an object and measure of measurement, measurement method, measuring instrument and measurement conditions.
Measurement objectit should be clean from extraneous inclusions if the density of the substance is measured, free from the effect of external interference (natural processes, industrial interference, etc.). The object itself should not have internal interference (the work of the measurement object itself).
Subject of measurement, i.e. the operator introduces the "personal" moment of measurement into the result, the element of subjectivism. It depends on the qualifications of the operator, sanitary and hygienic working conditions, the psycho-physiological state of the subject, on accounting for ergonomic requirements.
Method of measurement. Very often, the measurement of the same value of constant size by various methods gives various results, each of them has its drawbacks and advantages. The art of the operator is to eliminate or take into account factors distorting results. If the measurement fails to be performed so as to exclude or compensate for any factor affecting the result, then the latter in some cases make an appropriate amendment.
Influence S. The on-seasonable value in many cases is manifested as a perturbing factor, for example, the internal noise of measuring electronic amplifiers.
Another factor is the inertia of si. Some si give constantly inflated or constantly understated readings, which may be the result of a manufacturer's defect.
Terms of measureas affecting the factor include ambient temperature, humidity, atmospheric pressure, voltage in the network, etc.
Accounting for these factors implies an elimination of errors and amend the measured values.
Measurement methods are determined by the type of measured values, their dimensions required by the accuracy of the result required by the speed of the measurement process and other data.
There are many methods of measurement, and as science and technology develops and the number of them increases everything.
By a method for producing a numerical value of the measured value, all measurements are divided into three main types: direct, indirect and cumulative.
Straightthey are called measurements in which the desired value of the magnitude is directly from the experimental data (for example, the measurement of the mass on the dial or equal departure weights, the temperature is a thermometer, lengths - with linear measures).
Indirectmeasurements are called at which the desired value is found on the basis of the known relationship between this magnitude and values \u200b\u200bsubjected to direct measurements (for example, the density of a homogeneous body by weight and geometric sizes; determination of electrical resistance according to the results of measuring the voltage drop and current).
Cumulativemeasurements are called at the same time, several of the same names are measured simultaneously, and the desired value of the values \u200b\u200bare found by the solution of the system of equations obtained by direct measurements of various combinations of these values \u200b\u200b(for example, measurements in which the mass of individual dialing weights are installed according to the known mass of one of them and according to the results of direct Compare masses of various combinations of Giri).
Earlier it was said that in practice, direct measurements were most common due to their simplicity and velocity. We give a brief description of direct measurements.
Direct measurements of values \u200b\u200bcan be performed by the following methods:
1) Direct Assessment Method- The value of the value is determined directly via the verification device of the measuring instrument (measurement of pressure - spring pressure gauge, mass - dial weights, electric current forces - ammeter).
2) Comparison method with measure - the measured value is compared with the value of the reproducible measure (measurement of the mass by lever weights with balancing weights).
3) Differential method- The comparison method with a measure in which the difference between the measured value and the known value is valid for the measuring device, which is reproduced by measure (measurements performed when checking the length of the length of the sample measure on the comparator).
4) Zero method- Comparison method with measure when the resulting effect of exposure values \u200b\u200bon the comparison device is adjusted to zero (measuring the electrical resistance by the bridge with its full balancing).
5) Method of coincidence- The comparison method with a measure, in which the difference between the measured value and the value of the reproducible measure is measured using the coincidence of the scales or periodic signals (measurement of length using a nonius caliper, when there are matching marks on the calipers and noniural scales).
6) Method of substitution - the comparison method with a measure when the measured value is replaced by a known value reproducible to the measure (weighing with an alternate room of the measured mass and the weight of the same scales).
Chapter 1. Measuring physical quantities
A wide variety of phenomena with which you have to face practical activity, defines a wide range of quantities to be measured. The main object of studying in metrology is the measurement of physical quantities. In all cases of measurements, regardless of the value, method and measurement tools, there is general, which is the basis of measurements - this is a comparison of the size of a given value with a unit, a stored measuring means. With any measurement, using the experiment, we determine the quantitatively physical quantity in the form of a certain number of units taken for it, i.e. We find the value of the size of the physical size. Measurement is carried out with the use of a scale - a predetermined ordered set of a sequence of physical quantities adopted by agreement.
The choice of units of measurement values \u200b\u200bis of great importance for comparing the results performed using different methods, tools and in different measurement conditions. Therefore, it is customary to establish their size legislation. The international system of units approved by the XI General Conference on measures and weights created real prospects for the complete unification of the measurement units in all countries of the world community.
Measurement objects
Scale measurements
Scale measurement serves as the initial basis for measuring this value. It is an ordered set of values \u200b\u200bof magnitude.
Practical activities led to the formation of various types of measurement scales of physical quantities, the main of which are four considered below.
1. Scale order (ranks) is a ranked row – Ordered ascending or descending the sequence of values \u200b\u200bcharacterizing the property studied. It allows you to establish the ratio of order by increasing whether decreasing values, but there is no possibility to judge, how many times (or how much) more or less than one value compared to the other. In order scales in some cases, zero (zero mark) may exist, which is the absence of a measurement unit, because Its size cannot be installed, in these scales above the values, mathematical operations cannot be carried out (multiplication, summation).
An example of a scale of order is the Moos scale to determine hardness. This is a scale with reference dots, which contains 10 support (reference) minerals with various conditional numbers of hardness. Examples of such scales are also a beaufort scale for measuring the strength (speed) of the wind and the richter earthquake scale (seismic scale).
2. Interval scales (differences) It differs from the scale of the fact that for the measured values, not only the relationship of the order, but also the summation of the intervals (differences) between the various quantitative manifestations of properties is introduced. Difficult ranges may have conditional zero-repurries and units of measurements established by coordination. On the scale of intervals, it is possible to determine how much one value is greater or less, but it cannot be said how many times. The range of intervals measure time, distance (if the beginning of the path is not known), Celsius temperature, etc.
The scales of the intervals are more perfect than the scale of order. In these scales over the values, additive mathematical operations (addition and subtraction) can be carried out, but it is impossible - multiplicative (multiplication and division).
3. Collection of relationship Describes the properties of the values \u200b\u200bfor which the relationship of order, the summation of intervals and proportionality is applicable. In these scales, there is a natural zero and in coordination is dedicated by a unit of measurement. The ratio of the relationship is used to represent the measurement results obtained in accordance with the main measurement equation (1.1) by experimental comparison of the unknown value q with its unit [Q]. Examples of the scales of the relationship are mass scale, length, speed, thermodynamic temperature.
The ratio of relationship is the most perfect and most common of all measuring scales. This is the only scale at which you can set the value of the measured size. The scale of the relationship is to the relationship of any mathematical operations, which makes it possible to enter into the scales, multiplicative and additive amendments.
4. Absolute scale It has all the signs of the scale of relations, but in addition, it has a natural unambiguous definition of a unit of measurements. Such scales are used to measure relative values \u200b\u200b(reinforcement coefficients, attenuation, efficiency, reflection, absorption, amplitude modulation, etc.). A number of such scales are inherent in the borders concluded between zero and unit.
Scale of intervals and relationships combine the term "metric scales". The order scale refers to conditional scales, i.e. To the scales in which the unit of measurement is not defined and is sometimes called nonmetric. Absolute and metric scales are related to the category of linear. The practical implementation of the measurement scales is carried out by standardizing both the scales and units of measurements and, in the necessary cases, methods and conditions for their unambiguous reproduction.
The main units of S.
The main unit The values \u200b\u200bare called the unit of the main physical quantity, i.e. The values \u200b\u200bthat are conditionally adopted as an independent system of the system. When choosing the main units, the SI proceeded from that: 1) to cover the system for all areas of science and technology; 2) to create the basis for the formation of derived units for various physical quantities; 3) Take comfortable for practicing the size of the main units that have already received widespread; 4) Select units of such values \u200b\u200bwhose playback using the standards is possible with the greatest accuracy.
The main units of C, indicating the abbreviated designations with Russian and Latin letters are given in Table. 1.1.
Table 1.1.
The main units of S.
Definitions of major units that meet the decisions of the General Conference on Measures and Weighs, the following.
Meter It is equal to the length of the path passing by light in Vacuum for 1/299 792 458 share of a second.
Kilogram equal to the mass of the international prototype kilogram.
Second Equal to 9,192,631,770 radiation periods corresponding to the transition between two ultra-thin levels of the main state of the cesium-133 atom.
Ampere It is equal to the power of an immutable current, which, when passing along two parallel straight line conductors of the infinite length and a negligible area of \u200b\u200ba circular section, located at a distance of 1 m one from the other in vacuo, it causes a length of the interaction with a length of 1 m on each section of the conductor. × 10 -7 N.
Kelvin equal to 1/273,16 parts of the thermodynamic temperature of the triple point of water.
Mole It is equal to the amount of substance of the system containing the same structural elements as containing atoms in carbon-12 weighing 0.012 kg.
Kandela equal to the power of light in a given direction of the source emitting a monochromatic radiation with a frequency of 540 × 10 12 Hz, the energy force of the light of which in this direction is 1/683 W / cf.
Three first SI (meter, kilogram and second) can form derivative units for measuring mechanical and acoustic quantities. When the unit is added to them (Kelvin), you can form derivatives for measuring thermal values.
Meter, kilogram, second and ampere serve as the basis for the formation of derivatives of units in the field of electrical, magnetic measurements and measurements of ionizing radiation, and mools are used to form units in the field of physicochemical measurements.
Derivatives
Derivatives of the units of the international units are formed from the basic equations of communication between the values \u200b\u200bin which the numerical coefficients are equal to one. For example, to establish a unit of linear velocity V should be used by the equation of a uniform straight line
where L is the length of the path traveled (in meters); T - time (in seconds).
Consequently, the SI-meter speed unit per second is the speed of a straight and evenly moving point, at which it for the time 1 s is moving to a distance of 1 m.
The derivatives of units may be assigned to the names in honor of the well-known scientists. Thus, a pressure unit 1 N / m 2 was awarded a special name - Pascal (PA) named French mathematics and blouse physics Pascal. Derivative units that have special names are shown in Table. 1.2.
Table 1.2.
Derivative units of SI having special names
| Value | Unit | |||
| Name | Dimension | Name | Designation | Expression |
| Frequency | T -1. | hertz | Hz | C -1 |
| Strength, weight | LMT -2. | Newton | N. | m · kg · c -2 |
| Pressure, mechanical voltage | L -1 MT -2 | pascal | PA | M -1 · kg · s -2 |
| Energy, work, amount of heat | L 2 MT -2 | joule | J. | m 2 · kg · c -2 |
| Power | L 2 MT -3 | watt | T. | m 2 · kg · c -3 |
| Number of electricity | TI | pendant | CL | C · A. |
| Electrical Voltage, Potential | L 2 MT -3 i -1 | volt | IN | m 2 · kg · c -3 a -1 |
| Electrical Capacity | L -2 M -1 T 4 I 2 | Farad | F. | M -2 · kg -1 · C 4 · A 2 |
| Electrical resistance | L 2 MT -3 i -2 | Oh. | Oh. | m 2 · kg · c -3 · a -2 |
| Electrical conductivity | L -2 M -1 T 3 i 2 | Siemens | Cm | M -2 · kg -1 · C 3 · a 2 |
| Magnetic induction flow | L 2 MT -2 i -1 | Weber | Vb | m 2 · kg · c -2 · a -1 |
| Magnetic induction | MT -2 i -1 | tesla | TL | kg · c -2 · a -1 |
| Inductance | L 2 MT -2 i -2 | Henry | GN | m 2 · kg · c -2 · a -2 |
| Radionuclid activity | T -1. | Beckel | BK | C -1 |
| Absorbed dose of radiation | L 2 T -2 | Gray | G. | m 2 s -2 |
| Equivalent dose of radiation | L 2 T -2 | Sivert | ZV | m 2 · C -2 |
To measure flat and bodily angles in Si, radians and steradians are intended, respectively.
Radian(Running) - a unit of a flat angle - this is the angle between two radius of the circle, the arc between which is equal to the radius. In the degree of calculus radian is 57 ° 17 "48".
Steradian (cf) - a unit of a corporal angle is a bodily corner, the vertex of which is located in the center of the sphere and which cuts the area on the surface of the sphere equal to the square of the square side, along the length of the sphere radius.
By themselves, radians and steradian are used mainly for theoretical calculations, in practice the measurement of the corners are produced in angular degrees (minutes, seconds). It is in these units that most of the measurement tests are graduated.
Multiple and dolly units
There are multiple and dolle units of quantities. Multiple unit - This is a unit of physical quantity, for an integer in a number of times greater than a systemic or generated unit. For example, a kilometer length unit is 10 3 m, i.e. multiple meter. Dolly unit - Unit of physical quantity, the value of which is a number of times less than a systemic or generating unit. For example, a millimeter length is 10 -3 m, i.e. is a dollar.
For the convenience of applying units of physical quantities, the prefixes are taken to form the names of decimal multiple units and dolle units, Table. 1.3.
Table 1.3.
Farmers and consoles for the formation of decimal multiple and dolly units and their names
| Factor | Console | Designation of the console | |
| Russian | International | ||
| 10 24 | IOTTA | Y. | AND |
| 10 21 | Zetta | Z. | Z. |
| 10 18 | ex | E. | E. |
| 10 15 | Peta | P | R |
| 10 12 | Tera | T. | T. |
| 10 9 | Giga | G. | G. |
| 10 6 | mega | M. | M. |
| 10 3 | kilo | to | K. |
| 10 2 | hecto | G. | H. |
| 10 1 | dese | Yes | DA |
| 10 -1 | deci | D. | D. |
| 10 -2 | Santi | from | C. |
| 10 -3 | Milli | M. | M. |
| 10 -6 | micro | MK | M. |
| 10 -9 | Nano | N. | N. |
| 10 -12 | pico | P | P. |
| 10 -15 | Femto | F. | F. |
| 10 -18 | Atto | but | A. |
| 10 -21 | zepto | Z. | Z. |
| 10 -24 | Iokto | Y. | and |
In accordance with international rules, multiple and dollane units of the area and volume should be formed by attaching the prefixes to the original units. Thus, degrees relate to those units that were obtained as a result of the attachment of consoles. For example, 1 km 2 \u003d 1 (km) 2 \u003d (10 3 m) 2 \u003d 10 6 m 2.
Types and measurement methods
Measurement concept
Measurement is an essential concept in metrology. As mentioned above, it is the process of finding a physical value with the help of special technical means (measuring instruments). When measuring is carried out observations Behind the measurement object with the purpose of timely and correctly produce. The measurement object can be a technical device (for example, a chamber furnace), technological processes, the environment, consumption of substances and materials, human activity indicators, etc. The physical value that is chosen for measurements is called measured value.
In addition to the measured value of the measurement object and, accordingly, the measurement result is influenced by other physical quantities that are not measured by this measuring means. They are called influencing physical quantities. Influencing values \u200b\u200bare divided into the following groups:
climatic (ambient temperature, air humidity, atmospheric pressure);
electrical and magnetic (electric current fluctuations, voltage in the electrical circuit, the frequency of alternating current, the magnetic field);
external loads (vibrations, shock loads, ionizing radiation).
The effect of these values \u200b\u200bon the measurement result, as well as the imperfection of the manufacture of measuring instrument, the subjective errors of the human operator and a number of other factors are causes that determine the inevitable appearance of the measurement error.
The process of solving any measuring task includes, as a rule, three stages:
1) preparation for measurements (selection of methods and measuring instruments, ensuring the measurement conditions, etc.);
2) measurement (measuring experiment);
3) Processing measurement results.
In the process of the measuring experiment presented in Fig. 1.2, measurement object and measuring means are given in interaction. In this case, the measured value, affecting the measurement means, is converted to a certain signal that perceives a person or various technical devices - consumers of measuring information.
Fig. 1.2. Scheme of the process of obtaining measurement
This signal is functionally connected with the measured physical quantity, so it called the measuring signal information. Most often as signals use:
permanent level signals (constant electric current and voltage, compressed air pressure, light stream);
sinusoidal signals (alternating electric current and voltage);
the sequence of rectangular pulses (electric, light).
Perceived measuring information signals may further be processed with the aim of the most convenient representation of the measurement result. Such treatment may include statistical processing (with multiple measurements of magnitude), additional calculations (with indirect measurements), rounding, etc. Issues related to the processing of measurement results are discussed below (p. 2.4).
Classification of measurements
The measurements are very diverse, and they can be classified according to various features, the most important of which are reflected in Fig. 1.3.
Fig. 1.3. Classification of measurements
First, measurements are determined by the physical nature of phenomena (processes), in accordance with which there were certain sets of physical quantities related by nature or use in certain areas of science and technology, mechanical, thermal, physico-chemical and other measurements.
Secondly, measurements depending on the method of obtaining measurement results are divided into direct and indirect. Straight - These are measurements in which the desired value of physical quantity is directly from experienced data. In this case, the measurement object leads to interaction with the measurement means and according to its indications, the value of the measured value is determined. Examples of direct measurements: measurement of the length of the line, time with the help of hours, mass with weights, temperature - thermometer, current forces - ammeter, etc. To direct measurements include measurements of the overwhelming majority of technological processes.
Indirect - These are the measurements in which the desired value is determined based on the results of direct measurements, it is functionally connected with it. The value of q is found by calculating the formula
Q \u003d f (x 1, x 2, ... x m), (1.5)
where x 1, x 2, ... x m - the size of which are determined from direct measurements
Examples of indirect measurements: determination of the density of a homogeneous body for its mass and volume, electrical resistance of the conductor to the voltage drop and strength, power over current and voltage.
Indirect measurements are widespread in cases where the desired value is impossible or too difficult to measure directly or when the direct measurement gives a less accurate result. Their role is especially large in the measurement of values \u200b\u200binaccessible to direct experimental comparison, for example, the size of an astronomical or intra-industrial order.
According to metrological purposes, the measurement is divided into technical and metrological. Technical Measurements are carried out by working measurement tools in order to determine the value of the measured value, as well as during its control. These measurements are the most common and implemented in all industries and science. Metrological Measurements are performed using the standards in order to reproduce units of physical quantities and to transmit their size by working means of measurements (with calibration and calibration work carried out by metrological services).
According to the number of measurements made to obtain the result, the same and multiple measurements differ. Single They call the measurement executed once. For example, measurement time by hours. If a great confidence is needed in the result resulting, then spend multi-time Measurements of the same value for which the result of which is usually taken by the arithmetic value of individual measurements is usually for repeated measurements Number of measurements N ³3.
The dependence of the measured value of the measurement time is divided into static and dynamic. For static The measurements of the physical value are taken for constant during the measurement time (for example, the measurement of the length of the part at normal temperature). If the size of the physical size varies over time, then such measurements are called dynamic (for example, measuring the distance to the surface of the Earth with a declining aircraft).
Depending on the accuracy of the measurement tools used and the measurement conditions, they are divided into equal and inequillation. Equally accurate They call the measurements of the values \u200b\u200bmade with the same measurement to the same measurements in the same conditions with the same thorough. If the measurements were performed by the accuracy of measurement tools and (or) in different conditions, they are called non-equilibrium.
In addition to those shown in Fig. 1.3. Signs of measurement classification For specific cases, others can be used if necessary. For example, measurements can be divided depending on the place of execution on laboratory and industrial; Depending on the form of representation of the results - to absolute and relative.
The above measurements can be performed by various methods, i.e. ways to solve the measuring task.
Measurement methods
Method of measurement It is a reception or a set of comparison methods of a measured value with its unit in accordance with the implemented measurement principle. Under principle of measurements Understand the physical effects (phenomena) based on measurements. For example, temperature measurement using the thermoelectric effect. The measurement method is usually due to the measuring instrument.
There are many measurement methods, and with the development of science and technology, their number increases. Each physical value can be measured, as a rule, several methods. To systematize them, it is necessary to allocate general characteristic features. One such feature is the presence or absence of measure. Depending on this, two measurement methods are distinguished: the direct assessment method and the comparison method with measure (Fig. 1.4). Measurethey call the measurement means for playing and (or) storage of the physical size of one or more specified sizes, the values \u200b\u200bof which are expressed in the established units and are known with the necessary accuracy. Read more about the varieties of measures - see clause 3.1.
Fig. 1.4. Classification of measurement methods
Most common direct Assessment Method. Its essence is that the value of the measured value is determined directly by the measuring instrument, for example, a voltmeter voltage measurement, weighing the cargo on the spring weights (Fig. 1.5). In this case, the weight of the cargo x is determined on the basis of the measuring transformation by the value of the deformation D of the springs.
Fig. 1.5. Measurement scheme by direct assessment
Measurements using the direct assessment method are usually simple and do not require high operator skills, since it is not necessary to create special measuring settings and perform any complex calculations. However, the accuracy of measurements is most often turned out to be low due to the impact of the influencing values \u200b\u200band the need to graduate the scales of the instruments.
The most numerous group of instruments that serve to measure the direct assessment by the method are shown (incl. Switching devices). These include pressure gauges, dynamometers, barometers, ammeters, voltmeters, wattmeters, flow meters, liquid thermometers and many others. Measurements using an integrating device-counter or self-sash device are also attributed to the direct assessment method.
When conducting more accurate measurements, preference gives comparison method with measurein which the measured value is compared with the value reproduced by measure. A distinctive feature of this method is the direct participation of measure in the measurement process.
Comparison methods Depending on the presence or absence of a comparison between the measured value and the amount reproducible, the measure are subdivided into zero and differential. In both of these methods, opposition, substitution and coincidence are distinguished.
Zero measurement method -this is a method of comparison with measure , in which the resulting effect of the measured value and the measure on the comparison device is adjusted to zero. In this case, the value of the measured value is taken equal to the value of the measure. The coincidence of the values \u200b\u200bof the measured value and measure is noted using a zero pointer (zero indicator). Examples of the zero measurement method: weighing on equal departure weights; measurement of resistance, inductance and tanks using a balanced bridge; Measurement of temperature in an optical pyrometer using an incandescent sample lamp (respectively, the scales, the galvanometer and the human eye are zero pointers).
Differential measurement method (It is also called difference) is a comparison method with a measure at which the measured value is compared with the measure, and the difference between these two values \u200b\u200bis measured. The measure must have a value that slightly different from the value of the measured value. Example of a differential method: Measurement of the length of the part on the difference between the measured length and end measure of the length (in the range of linear and angular measurements, this method is called relative); measurement of resistance, inductance and containers using an unbalanced bridge; Weighing on non-equal balance. The use of a zero pointer in this method is not required.
Method of oppositionit is that the measured value and the value reproduced by the measure simultaneously affect the comparison device by which the relationship between these values \u200b\u200bis established. An example of a zero method of controversy is weighing the goods x on the equal departure weights (Fig. 1.6, a), when the measured weight of the cargo x is equal to the weight of the weight, balancing it. The equilibrium state is determined by the position of the zero indicator pointer (it must be on the zero mark). When weighing the cargo in the case of a differential method of opposition, the weight of the load x is equalized by weight of the weight and the power of the elastic deformation of the spring (Fig. 1.6, b), the value of which is counted on the scale of the instrument. The weight of the cargo is determined as the sum of the mass of weights and indications counted on the scale.
 |
| but) |
 |
| b) |
Fig. 1.6. Measurement diagram by comparison with measure: A - zero, b - differential
The opposition method is widely used to measure various physical quantities. As a rule, it provides greater accuracy of measurement than the method of direct assessment, by reducing the impact on the measurement result of the measurement measurement and affecting the values.
The species of the comparison method with measure belongs to method of substitutionExactly used in the practice of accurate metrological studies. The essence of the method is that the measured value is replaced by measure with a known value of the value, i.e. The measured value and measure sequentially affect the measuring instrument. In the zero method, the measurement of the measured measure is performed, and the measurement result is taken equal to the measure value. In the differential method, it is not possible to carry out complete substitution and to obtain the value of the measured value to the value, the value should be added to the value of the instrument reading.
Due to the fact that the measured value and measure are included in one another in the same part of the measuring circuit of the instrument, the measurement accuracy is significantly increased compared with the measurements carried out using other species of the comparison method, where the asymmetry of the chains in which compared values \u200b\u200bare included, leads to the emergence of systematic errors. The substitution method is often used in electrical measurements using AC bridges.
Method of coincidenceit is a kind of comparison method with a measure in which the difference between the measured value of the value and the value reproducible is measured using the coincidence of the scales or periodic signals. On the principle of the coincidence method, Nonius was built, which is part of a number of measuring instruments (for example, a caliper).
In addition to the considered measurement methods, contact and contactless contacts are also distinguished depending on the presence (or absence) of the direct contact between the sensitive element of the measurement tool and the measurement object. Examples of the contact method - measurement of the diameter of the shaft caliper, measuring the temperature of the body thermometer. Examples of the contactless method - measurement of temperature in the blast furnace with a pyrometer, measurement of the distance to the object with a radar.
Measurement errors
The result of measurements of the value depends on many factors: the choice of the method and means of measurements, the conditions of its implementation (for example, temperature, pressure, environmental humidity), the method of processing measurement results, the qualifications of the operator, performing measurements, etc. The specified factors lead to the difference in value The result of measuring the magnitude and its true meaning, i.e. For errors. One of the main objectives of metrology is to develop methods for determining measurement errors.
Depending on the degree of approximation to the objectively existing value of the value, the true value of the value and the result of its measurement, as well as its actual value, should be distinguished.
True meaningX and value value, an ideal way characterizing in high-quality and quantitative terms the corresponding physical quantity. It can only be obtained as a result of an infinite measurement process with infinite improvement of methods and measuring instruments.
Measurement resultsX C change the value obtained in its measurement using specific methods and measuring instruments.
Measurement results error (or measurement error) D is the deviation of the measurement result from the true value of the measured value, i.e.
D \u003d X variations and.
But since the true meaning of the measured value is unknown, it is definitely unknown and measurement errors, so in practice, the so-called valid value of the magnitude is used to determine the error, which replace the true value.
Value valueX d values – this value obtained experimentally and is so close to the true meaning that in the set measuring task can be used instead. The actual value is found more accurate methods and measurement tools. The higher the accuracy of the means and the measurement method, with the help of which the X D, with greater confidence it is considered as close to the true one. Therefore, in practice, the measurement error D (here is due to the absolute error) are found by the formula
D \u003d x meas - x d (1.6)
It is impossible to completely eliminate errors, but you can reduce them using the methods discussed below.
Accuracy of measurement results - This is one of the most important characteristics (indicators) of measurement quality, reflecting the proximity to zero the error of the measurement result. In addition, measurement quality indicators are convergence, reproducibility, correctness and accuracy of measurement results, which will be discussed below.
Rule three sigm
The characteristic property of the normal distribution is that in the range of ± 1s] is about 68% of all its measurement results. In the interval ± 2s] - 95%. In the range ± 3s] - 99.73% (Fig. 1.12). Therefore, almost all measurement results lie in the 6s interval (three s per side of M [x]). Outside of this interval, 0.27% of data from their total number may be located (approximately three of the thousands of measurement results).
Fig. 1.12. Stock Illustration Rule three sigm
It follows that if any value of the value goes beyond ± 3s, then with a high probability it can be considered erroneous.
Based on this formulated rule three sigm: If, with multiple measurements (n\u003e 25 ... 30), the same size of a constant size of the doubtful result X SBU of a separate measurement (maximum or minimum) differs from the average value of more than 3s, then with a probability of 99.7% it is erroneous, t ..
if\u003e 3S, (1.12)
x dun is a miss; It is discarded and not taken into account with the further processing of measurement results.
The law of normal distribution works with the number of measurement results N \u003d ¥. In reality, a finite number of measurements are obtained, which are subject to the law of the distribution of Student. For n\u003e 25, Student's distribution seeks normal.
Chapter 2. Measurement Means
One of the most important elements of the measurement process that allows you to directly receive measuring information is a measurement tool. Every day, a huge amount of measurements are carried out with the help of a "army" of a variety of measuring instruments. There are many of them, they can be easy to use, such as a ruler, or represent the most complex devices that require highly qualified maintenance, such as a radionavigation system. Regardless of the complexity, destination and principle of operation, they all perform the same function - compare the unknown size of the physical size with its unit. At the same time, it is important that the measurement means "skillful" store (and reproduce) a unit of physical quantity in such a way that the requirement is made that the stored unit is unchanged during the time. It is this "skillful storage" distinguishes the means of measurements from other technical means. In this way, measurement is a technical means (or their complex), intended for measurements, having normalized metrological characteristics, reproducing and (or) storing a unit of physical quantity, the size of which is accepted unchanged (at the forecloser
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