Measurement of physical quantities of the measurement technique. Measurement technique
MINISTRY OF EDUCATION OF THE RUSSIAN FEDERATION STATE INSTITUTION
KUZBAS STATE TECHNICAL UNIVERSITY Department of machine tools and tools
METROLOGY
METHODS AND INSTRUMENTS FOR MEASURING PHYSICAL QUANTITIES
Guidelines for laboratory work on the course "Metrology, standardization and certification" for students of specialty 120200 "Metal-cutting machines and tools" of specialization 120219 "Quality management, certification and equipment licensing"
Compiled by N.G. Rozenko
Approved at the meeting of the department Minutes No. 5 dated 30.10.02
An electronic copy is stored in the library of the main building of the KuzGTU
Kemerovo 2003
quantities, methods, techniques, as well as measuring instruments for metrological support of production.
2. THEORETICAL PROVISIONS A physical quantity is one of the properties of a physical object.
project, physical system, phenomenon or process. Qualitatively, this property is one for many physical objects, but quantitatively it is individual for each of them. The quantitative certainty of a physical quantity inherent in a particular material object, system, phenomenon, process is called the size of a physical quantity. The value of a physical quantity is formed by expressing a physical quantity in the form of a certain number of units accepted for it.
The value of a physical quantity that ideally characterizes the corresponding physical quantity qualitatively and quantitatively is called the true value of the quantity. It can be correlated with the concept of absolute truth and can only be obtained as a result of an endless process of measurements with an endless improvement in methods and measuring instruments.
The actual value of a physical quantity is the value of a physical quantity obtained experimentally and so close to the true value that it can be used instead of it in the set measurement task.
Aggregate physical quantities, formed in accordance with accepted principles, is called a system of physical quantities.
In the system of physical quantities, some quantities are taken as independent, while others are defined as functions of independent quantities.
A physical quantity included in a system of quantities and conditionally accepted as independent of other quantities of this system is called the main physical quantity.
A physical quantity included in a system of quantities and defined through the basic quantities of this system is called a derivative physical quantity.
The measurement of a physical quantity is a set of operations for the use of a technical means that stores a unit of a physical quantity, ensuring that the ratio is found in explicit or implicit
explicit form of the measured quantity with its unit and obtaining the value of this quantity. If a series of measurements of any value is made by measuring instruments of the same accuracy under the same conditions with the same accuracy, then such measurements are called equal-precision. If a series of measurements of any value is made by measuring instruments differing in accuracy and (or) under different conditions, then such measurements are called unequal measurements.
If the measurement is performed once, then it is called single. A measurement is called multiple if, when measuring a physical quantity of the same size, the result is obtained from several successive measurements, i.e. consisting of a number of single measurements.
A static measurement is a measurement of a physical quantity, taken in accordance with a specific measurement task as unchanged over the measurement time.
A dynamic measurement is a measurement of a physical quantity that changes in size.
A measurement based on direct measurements of one or more basic quantities and (or) the use of physical constant values is called an absolute measurement. For example, the measurement of force F = m g is based on the use of the main mass value - m
and using the physical constant g at the mass measurement point. A relative measurement is a measurement of the ratio of a quantity to
the value of the same name, which plays the role of a unit, or the measurement of the change in the value in relation to the value of the same name, taken as the original.
A measurement in which the initial value of a physical quantity is obtained directly is called a direct measurement. For example, measuring the length of a part with a micrometer, current strength with an ammeter, mass on a scale.
If the desired value of a physical quantity is determined on the basis of direct measurements of other physical quantities that are functionally related to the desired quantity, then such measurements are called indirect. For example, the density D of a cylindrical body can be determined based on the results of direct measurements of the mass m, height h and cylinder diameter d, related to the density by the equation
0.25π d 2 h |
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Simultaneous measurements of several quantities of the same name, in which the desired values of the quantities are determined by solving a system of equations obtained by measuring these quantities in different combinations, are called cumulative measurements. For example, the value of the mass of individual weights of the set is determined by the known value of the mass of one of the weights and by the results of measurements (comparisons) of the masses of various combinations of weights.
If two or more quantities of the same name are measured simultaneously to determine the relationship between them, then such measurements are called joint.
The type of measurements is a part of the measurement area, which has its own characteristics and is distinguished by the uniformity of the measured values. For example, in the field of electrical and magnetic measurements, the following types of measurements can be distinguished: measurements of electrical resistance, electromotive force, electrical voltage, magnetic induction, etc.
A subspecies of measurements is a part of the type of measurements that highlights the features of measurements of a homogeneous quantity (by range, by the size of the quantity, etc.). For example, when measuring length, measurements of large lengths (in tens, hundreds, thousands of kilometers) or measurements of extra small lengths - film thicknesses.
Measuring instruments are technical means specially designed for measurements. Measuring equipment includes measuring instruments and their combinations (measuring systems, measuring installations), measuring accessories, measuring installations.
A measuring instrument is understood as a technical instrument intended for measurements, having normalized metrological characteristics, reproducing and (or) storing a unit of physical quantity, the size of which is assumed to be unchanged within the established error for a known time interval.
A working measuring instrument is a measuring instrument intended for measurements not related to the transfer of the unit size to other measuring instruments.
The main measuring instrument is a means of measuring the physical quantity, the value of which must be obtained in accordance with the measurement task.
An auxiliary measuring instrument is a measuring instrument of that physical quantity, the influence of which on the main measuring instrument or the measurement object must be taken into account in order to obtain measurement results of the required accuracy. For example, a thermometer for measuring the temperature of a gas when measuring the volume flow of that gas.
A measuring instrument is called automatic if it, without the direct participation of a person, makes measurements and all operations related to the processing of measurement results, their registration, data transmission or generation of a control signal. An automatic measuring instrument built into an automatic production line is called a measuring machine or a control machine. A variety of control and measuring machines, characterized by good handling properties, high speeds of movement and measurement, is called measuring robots.
A measuring instrument is called automated if it automatically performs one or part of the measuring operations. For example, a barograph measures and records pressure; the electric energy meter measures and records data on an accrual basis.
A measure of a physical quantity is a measuring instrument designed to reproduce and (or) store the physical quantity of one or more given parameters, the values of which are expressed in established units and are known with the required accuracy.
There are the following types of measures.
1. An unambiguous measure is a measure that reproduces a physical quantity of the same size (for example, a weight of 1 kg).
2. A multi-valued measure is a measure that reproduces a physical quantity of different sizes (for example, a dashed measure of length).
3. A set of measures is a set of measures of different sizes of the same physical quantity, intended for practical use both individually and in various combinations (for example, a set of gage blocks).
4. A measure box is a set of measures structurally combined into a single device, which has devices for connecting them in various combinations (for example, an electrical resistance box).
A measuring set is a measuring instrument designed to obtain measurement values of a physical quantity within a specified range. According to the method of indicating the values of the measured value, measuring instruments are divided into indicating and recording. According to the action, measuring instruments are divided into integrating and summing. There are also direct action devices and comparison devices, analog and digital devices, self-recording and printing devices.
A set of functionally combined measures, measuring instruments, measuring transducers and other devices designed to measure one or more physical quantities and located in one place is called a measuring installation. The measuring setup used for verification is called a calibration setup. The measuring setup that is part of the standard is called the reference setup. Some large measuring devices are called measuring machines. Measuring machines are designed for precise measurements of physical quantities. For example, a force measuring machine, a machine for measuring large lengths in industrial production, a dividing machine, a coordinate measuring machine.
A measuring system is a set of functionally integrated measures, measuring instruments, measuring transducers, computers and other technological means located in different points controlled object for the purpose of measuring one or more physical quantities inherent in this object, and generating measuring signals for various purposes. Depending on the purpose, measuring systems are divided into measuring informing, measuring control systems, etc. A measuring system that is reconfigured depending on a change in the measuring task is called a flexible measuring system.
A standard sample is a sample of substances or material with the values of one or more quantities established as a result of metrological certification, characterizing the property or composition of this substance or material. A distinction is made between property standards and composition standards. An example of a property standard is the relative permittivity standard. Standard samples of the properties of substances and materials for metrological purposes play the role of unambiguous measures. They can be used as working standards with sizing
according to the state verification scheme. An example of a composition standard is a carbon steel composition standard.
A measuring transducer is a technical tool with normalized metrological characteristics that is used to convert a measured value into another value or a measuring signal that is convenient for processing, storage, further transformations, indication or transmission. The measuring transducer can be part of a measuring device, measuring installation, measuring system etc. or be used together with any measuring instrument. According to the nature of the conversion, analog, digital-to-analog, analog-to-digital converters are distinguished. Primary and intermediate transducers are distinguished by place in the measuring circuit. Converters are also large-scale and transmitting.
Converter examples.
1. Thermocouple in thermoelectric thermometer;
2. Electropneumatic converter.
The primary measuring transducer is a measuring transducer, which is directly affected by the measured physical quantity. For example, a thermocouple in a thermoelectric thermometer circuit.
A sensor is a structurally separate primary transducer from which measuring signals are received.
A comparison tool is a technical tool or a specially created environment by which it is possible to compare measures of homogeneous quantities or readings of measuring instruments with each other.
Examples of means of comparison.
1. Lever scales, on one cup of which a reference weight is installed, and on the other, a calibrated one.
2. Calibration fluid for comparing reference and working hydrometers.
3. The temperature field created by a thermostat for comparing thermometer readings.
4. The pressure of the medium created by the compressor can be measured with a calibrated and reference pressure gauge at the same time; on the basis of the readings of the reference instrument, the instrument under test is calibrated.
A comparator is a comparison tool designed to compare measures of homogeneous quantities. For example, lever scales.
A measuring instrument recognized as fit and approved for use by an authorized body is called a legalized measuring instrument.
State standards of the country become such as a result of the approval of primary standards by the national body for standardization and metrology. Working measuring instruments intended for serial production are legalized by approving the type of measuring instrument.
Measuring accessories are auxiliary tools that serve to ensure necessary conditions to perform measurements with the required accuracy. Examples of measuring accessories are thermostats, barometers, anti-vibration foundations, electromagnetic shielding devices, instrument tripods, etc.
An indicator is a technical tool or substance designed to establish the presence of a physical quantity or exceed its threshold value. The signal proximity indicator is called a null indicator.
Examples of indicators.
1. The oscilloscope serves as an indicator of the presence or absence of measurement signals.
2. Litmus paper or other substances in chemical reactions.
3. Light or sound signal of the indicator of ionizing radiation in case of excess of the radiation level of the threshold value.
A metrological characteristic of measuring instruments is a characteristic of one of the properties of measuring instruments that affects the measurement result and its error. For each type of measuring instruments, their metrological characteristics are established. The metrological characteristics established in normative and technical documents are called normalized metrological characteristics, and those determined experimentally are called actual metrological characteristics.
The variation of the readings of the measuring device is the difference in the readings of the device at the same point in the measurement range with a smooth approach to this point from the side of smaller and large values measured value.
The range of indications of measuring instruments is the range of values of the instrument scale, limited by the initial and final values of the scale.
The measurement range of measuring instruments is the range of values of a quantity within which the permissible error limits of measuring instruments are normalized.
The quantity values that limit the measurement range from below and above (left and right) are called the lower measurement limit and the upper measurement limit, respectively.
The nominal value of a measure is the quantity value assigned to a measure or batch of measures during manufacture, for example a weight with a nominal value of 1 kg.
The actual value of a measure is the quantity value assigned to the measure on the basis of its calibration or verification. For example, the composition of the state standard of the unit of mass includes a platinum-iridium weight with a nominal mass value of 1 kg, while the actual value of its mass is 1.000000087 kg, obtained as a result of international comparisons with the international standard of the kilogram, stored at the International Bureau of Weights and Measures (BIPM).
The sensitivity of a measuring instrument is a property of a measuring instrument, determined by the ratio of the measurement of the output signal of this instrument to the change in the measured value that causes it. There is a difference between absolute and relative sensitivity. Absolute sensitivity is determined by the formula
where X is the measured value.
The sensitivity threshold is a characteristic of a measuring instrument in the form of the smallest value of a change in a physical quantity, starting from which it can be measured by this instrument.
Zero offset is the non-zero reading of a measuring instrument when the input signal is zero.
Drift of the readings of a measuring instrument is a change in the readings of a measuring instrument in time, due to changes in influencing quantities or other factors.
The type of measuring instrument is a set of measuring instruments of the same purpose, based on the same principle
actions having the same design and manufactured according to the same technical documentation. Measuring instruments of the same type may have different modifications (for example, differ in the measurement range).
The type of measuring instrument is a set of measuring instruments intended for measuring a given physical quantity. For example, ammeters and voltmeters are types of measuring instruments, respectively, for the strength of electric current and voltage. The type of measuring instruments may include several types.
The metrological serviceability of measuring instruments is their condition in which all normalized metrological characteristics meet the established requirements.
The output of the metrological characteristics of the measuring instrument beyond the established limits is called the metrological failure of the measuring instrument.
The physical phenomenon or effect underlying the measurement is called the principle of measurement (for example, the use of gravity when measuring mass by weighing).
A measurement method is a technique or a set of methods for comparing a measured physical quantity with its unit in accordance with the implemented measurement principle. The measurement method is interconnected with the device of measuring instruments.
The method of direct assessment is a method of measurement in which the value of a quantity is determined directly from the indicating measuring instrument.
A comparison method with a measure is a method of measurement in which the quantity being measured is compared with the quantity reproducible by the measure. For example, measurements of mass on a balance scale with weights (measures of mass with a known value).
The null method of measurement is a method of comparison with a measure in which the net effect of the measurand and the measure on the comparator is brought to zero. For example, the measurement of electrical resistance by a bridge with its full balancing.
The method of measurement by substitution is a method of comparison with a measure in which the measurand is replaced by a measure with a known value of the quantity. For example, weighing with alternate placement of the measured mass and weights on the same scale pan.
The method of measurement by addition is a method of comparison with a measure, in which the value of the measured quantity is supplemented by a measure of the same
Measurement of a physical quantity- a set of operations on the use of a technical means that stores a unit of a physical quantity, providing a ratio (in an explicit or implicit form) of the measured quantity with its unit and obtaining the value of this quantity.
In the simplest case, by applying a ruler with divisions to any part, in fact, its size is compared with the unit stored by the ruler, and, after counting, the value of the value (length, height, thickness and other parameters of the part) is obtained. With the help of a measuring device, the size of the value converted into the movement of the pointer is compared with the unit stored by the scale of this device, and a reading is taken.
The definition of the concept "measurement" satisfies the general equation of measurements, which is essential in ordering the system of concepts in metrology. It takes into account the technical side (a set of operations), reveals the metrological essence of measurements (comparison with the unit) and shows the epistemological aspect (obtaining the value of a quantity).
Measurement types
Measurement area- a set of measurements of physical quantities characteristic of any field of science or technology and distinguished by their specificity. Note - There are a number of measurement areas: mechanical, magnetic, acoustic, measurements of ionizing radiation, etc.
Type of measurement- a part of the measurement area, which has its own characteristics and is characterized by the uniformity of the measured values. EXAMPLE In the field of electrical and magnetic measurements, the following types of measurements can be distinguished: measurements of electrical resistance, electromotive force, electrical voltage, magnetic induction, etc.
There are several types of measurements.
According to the nature of the dependence of the measured value on time, the measurements are divided into:
static measurements;
dynamic measurements.
According to the method of obtaining measurement results, they are divided into:
indirect;
cumulative;
joint.
According to the conditions that determine the accuracy of the result, the measurements are divided into:
metrological measurements;
control and verification measurements;
technical measurements.
According to the way the results are expressed:
absolute measurements;
relative measurements.
According to the characteristics of the measuring instrument, there are:
equal measurements;
uneven measurements.
By the number of measurements in a series of measurements:
single measurements;
multiple measurements.
Measurements are distinguished by the method of obtaining information, by the nature of changes in the measured value during the measurement process, by the amount of measurement information, in relation to the main units.
According to the method of obtaining information, measurements are divided into direct, indirect, cumulative and joint.
Direct measurements are a direct comparison of a physical quantity with its measure. For example, when determining the length of an object with a ruler, the desired value (a quantitative expression of the length value) is compared with a measure, i.e. a ruler.
Indirect measurements - differ from direct ones in that the desired value of a quantity is established based on the results of direct measurements of such quantities that are associated with the desired specific dependence. So, if you measure the current strength with an ammeter, and the voltage with a voltmeter, then according to the known functional relationship of all three quantities, you can calculate the power of the electrical circuit.
Aggregate measurements - are associated with the solution of a system of equations compiled from the results of simultaneous measurements of several homogeneous quantities. The solution of the system of equations makes it possible to calculate the desired value.
Joint measurements are measurements of two or more inhomogeneous physical quantities to determine the relationship between them.
Cumulative and joint measurements are often used in the measurement of various parameters and characteristics in the field of electrical engineering.
According to the nature of the change in the measured value during the measurement process, there are statistical, dynamic and static measurements.
Statistical measurements are associated with the determination of the characteristics of random processes, sound signals, noise levels, etc. Static measurements take place when the measured value is practically constant.
Dynamic measurements are associated with such quantities that undergo certain changes during the measurement process. Ideal static and dynamic measurements are rare in practice.
According to the amount of measurement information, single and multiple measurements are distinguished.
Single measurements are one measurement of one quantity, i.e. the number of measurements is equal to the number of measured quantities. The practical application of this type of measurement is always associated with large errors, therefore, at least three single measurements should be carried out and the final result should be found as the arithmetic mean.
Multiple measurements are characterized by an excess of the number of measurements of the number of measured values. The advantage of multiple measurements is a significant reduction in the influence of random factors on the measurement error. measurement metrological scale
Measurement methods are determined by the type of measured quantities, their dimensions, the required accuracy of the result, the required speed of the measurement process, and other data.
There are many methods of measurement, and with the development of science and technology, their number is increasing.
According to the method of obtaining the numerical value of the measured value, all measurements are divided into three main types: direct, indirect and cumulative.
Direct measurements are called in which the desired value of a quantity is found directly from experimental data (for example, mass measurement on a dial or equal-arm balance, temperature - with a thermometer, length - with the help of linear measures).
indirect measurements are called in which the desired value of a quantity is found on the basis of a known relationship between this quantity and the quantities subjected to direct measurements (for example, the density of a homogeneous body in terms of its mass and geometric dimensions; determination of electrical resistance from the results of measuring the voltage drop and current strength).
Aggregate called measurements in which several quantities of the same name are measured simultaneously, and the desired value of the quantities is found by solving a system of equations obtained by direct measurements of various combinations of these quantities (for example, measurements in which the masses of individual weights of a set are determined from the known mass of one of them and from the results of direct comparisons of the masses of various combinations of weights).
Earlier it was said that in practice direct measurements are most widely used due to their simplicity and speed of execution. Let's give brief description direct measurements.
Direct measurements of quantities can be made by the following methods:
1) Direct evaluation method - the value of the quantity is determined directly by the reading device of the measuring device (pressure measurement - with a spring pressure gauge, mass - with dial scales, electric current - with an ammeter).
2) Measure comparison method – the measured value is compared with the value reproduced by the measure (measurement of the mass by a balance scale with weights).
3) Differential Method - a method of comparison with a measure, in which the measuring instrument is affected by the difference between the measured value and the known value reproduced by the measure (measurements performed when checking length measures by comparison with a standard measure on a comparator).
4) Zero method - a method of comparison with a measure, when the resulting effect of the impact of quantities on the comparison device is brought to zero (measurement of electrical resistance by a bridge with its full balancing).
5) Match method - a method of comparison with a measure, in which the difference between the measured value and the value reproduced by the measure is measured using the coincidence of scale marks or periodic signals (length measurement using a vernier caliper when observing the coincidence of marks on the vernier caliper and vernier scales).
6) substitution method – a method of comparison with a measure, when the measured value is replaced by a known value, a reproducible measure (weighing with alternate placement of the measured mass and weights on the same scale pan).
End of work -
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All topics in this section:
The concept of metrology as a science
Metrology is the science of measurements, methods and means of ensuring their unity and ways to achieve the required accuracy. In practical life, a person
The concept of measuring instruments
A measuring instrument (MI) is a technical tool (or a set of technical means) intended for measurement, which has a normalized metrological character.
Metrological characteristics of measuring instruments
Metrological characteristics of measuring instruments are characteristics of properties that affect the results and measurement errors. Appointment information meter
Factors affecting measurement results
In metrological practice, when carrying out measurements, it is necessary to take into account a number of factors that affect the measurement results. This is the object and subject of measurement, the method of measurement, cf.
Formation of the measurement result. Measurement errors
The measurement procedure consists of the following main stages: 1) acceptance of the object measurement model; 2) choice of measurement method; 3) choice of measuring instruments;
Presentation of measurement results
There is a rule: measurement results are rounded up to the nearest "error". In practical metrology, rules for rounding off results and measurement errors have been developed. os
Causes of measurement errors
There are a number of error terms that dominate the total measurement error. These include: 1) Errors depending on the means of measurement. But
Handling multiple measurements
We assume that the measurements are equal, i.e. performed by one experimenter, under the same conditions, with one device. The technique boils down to the following: n observations are made (one
Student's distribution (t-test)
n/α 0.40 0.25 0.10 0.05 0.025 0.01 0.005 0.0005
Measurement techniques
The main loss of accuracy in measurements occurs not due to a possible metrological malfunction of the measuring instruments used, but primarily due to the imperfection of the method.
The concept of metrological support
Metrological support (MO) is understood as the establishment and application of scientific and organizational foundations, technical means, rules and norms, necessary
System approach in the development of metrological support
When developing MO, it is necessary to use a systematic approach, the essence of which is to consider 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. Individual aspects of MO are considered in the recommendation
Legislation of the Russian Federation on ensuring the uniformity of measurements
The regulatory framework for ensuring the uniformity of measurements is shown in Figure 2.
National system for ensuring the uniformity of measurements
The National System for Ensuring the Uniformity of Measurements (NSMEI) is a set of rules for performing work to ensure the uniformity of measurements, its participants and rules
The main types of metrological activities to ensure the uniformity of measurements
The unity of measurements is understood as such a state of measurements, in which their results are expressed in legal units of quantities and errors (indefinitely
Conformity assessment of measuring instruments
When carrying out measurements related to the sphere of state regulation of ensuring the uniformity of measurements, on the territory of Russia, SI must be used that meet the requirements
Approval of the type of measuring instruments
Type approval (except for SOSSVM) is carried out on the basis of positive test results. Approval of the type of SOSSVM is carried out on the basis of positive results of the atte
Measurement procedures certification
A measurement technique is a set of operations and rules, the implementation of which ensures that a measurement result is obtained with a specified error.
Verification and calibration of measuring instruments
Verification of measuring instruments is a set of operations performed in order to confirm the conformity of the actual values of the metrological characteristics
Structure and functions of the metrological service of an enterprise, organization, institution that is a legal entity
The metrological service of an enterprise, organization and institution enjoying the rights of a legal entity, regardless of the form of ownership (hereinafter - the enterprise) includes a department (service)
The concept of interchangeability
Interchangeability is the property of the same parts, components or assemblies of machines, etc., which allows you to install parts (assemblies, assemblies) during assembly or replacement
Qualities, main deviations, landings
The accuracy of a part is determined by the accuracy of dimensions, the roughness of surfaces, the accuracy of the shape of surfaces, the accuracy of location and the waviness of surfaces. To ensure
Designation of tolerance fields, limit deviations and landings in the drawings
Limit deviations of linear dimensions are indicated on the drawings by conditional (letter) designations of tolerance fields or numerical values of limit deviations, as well as letter
Unspecified limit deviations of dimensions
Limit deviations not indicated directly after the nominal dimensions, but stipulated by a general entry in technical requirements drawing, are called unspecified limit deviations.
Recommendations for the use of clearance fits
H5/h4 fit (Smin= 0 and Smax = Td +Td) is assigned to couples with precise centering and direction, in which rotation and longitudinal movement are allowed
Recommendations for the use of transitional landings
Transition fits H / js, H / k, H / m, H / n are used in fixed detachable joints for centering interchangeable parts or parts that, if necessary, can move in
Tips for Using Interference Fits
Landing N/r; Р/h - "lightly pressed" - are characterized by a minimum guaranteed tightness. Installed in the most accurate qualifications (shafts 4 - 6th, holes 5 - 7-
The concept of surface roughness
Surface roughness according to GOST 25142 - 82 is a set of surface irregularities with relatively small steps, selected using the base length. Bazova
Roughness parameters
According to GOST 2789 - 73, the surface roughness of products, regardless of the material and method of manufacture, can be evaluated by the following parameters (Figure 10):
General terms and definitions
The tolerances of the shape and location of the surfaces of machine parts and instruments, terms, definitions related to the main types of deviations are standardized by GOST 24642 - 81. The basis
Form deviations and tolerances
Form deviations include deviations of straightness, flatness, roundness, profile of the longitudinal section and cylindricity. Deviations in the shape of flat surfaces
Deviations and location tolerances
The deviation of the location of the surface or profile is the deviation of the actual location of the surface (profile) from its nominal location. Quantitative location deviations about
Total deviations and tolerances of the shape and location of surfaces
The total deviation of the form and location is the deviation, which is the result of the joint manifestation of the deviation of the form and the deviation of the location of the element in question (according to
Dependent and independent shape and location tolerance
The location or shape tolerances set for shafts or holes can be dependent and independent. Dependent is the tolerance of the shape or location, the minimum value
Numerical values of tolerances of the shape and location of surfaces
According to GOST 24643 - 81, 16 degrees of accuracy are established for each type of tolerance of the shape and location of surfaces. The numerical values of tolerances change from one degree to another
Designation in the drawings of shape and location tolerances
The type of tolerance of the shape and location according to GOST 2.308 - 79 should be indicated in the drawing with the signs (graphic symbols) given in table 4. I enter the sign and numerical value of the tolerance
Unspecified shape and location tolerances
Directly in the drawing, as a rule, the most critical tolerances for the shape and location of surfaces are indicated. According to GOST 25069 - 81, all indicators of form accuracy and location
Rules for defining bases
1) If the part has more than two elements for which the same unspecified location or runout tolerances are established, then these tolerances should be attributed to the same base;
Rules for determining the defining size tolerance
The defining tolerance of a size is understood as: 1) When determining an unspecified tolerance of perpendicularity or end runout, the tolerance of a size coordinating
Surface waviness
Surface waviness is understood as a set of periodically repeating irregularities, in which the distances between adjacent hills or depressions exceed the base length l.
Rolling bearing tolerances
The quality of bearings, other things being equal, is determined by: 1) the accuracy of the connecting dimensions and the width of the rings, and for roller angular contact bearings e
Selection of rolling bearing fits
The fit of the rolling bearing on the shaft and in the housing is selected depending on the type and size of the bearing, its operating conditions, the value and nature of the loads acting on it and the type of loading of the rings
Solution
1) With a rotating shaft and a constant force Fr, the inner ring is loaded with circulation loads, and the outer ring with local loads. 2) Load intensity
Bearing symbols
The system of symbols for ball and roller bearings is established by GOST 3189 - 89. The symbol of a bearing gives a complete picture of its overall dimensions, design, manufacturing accuracy.
Angular tolerances
Tolerances of angular dimensions are assigned according to GOST 8908 - 81. Tolerances of angles AT (from the English. Angle tolerance - angle tolerance) should be assigned depending on the nominal length L1 of the smaller side
System of tolerances and landings for conical connections
A conical connection has advantages over a cylindrical one: it is possible to adjust the amount of clearance or interference by relative displacement of parts along the axis; with a fixed connection
The main parameters of the metric fastening thread
Cylindrical thread parameters (Figure 36, a): average d2 (D2); outer d (D) and inner d1 (D1) diameters on
General principles of interchangeability of cylindrical threads
Tolerance and fit systems that ensure the interchangeability of metric, trapezoidal, thrust, pipe and other cylindrical threads are built on a single principle: they take into account the presence of mutual
Tolerances and fits of threads with clearance
Tolerances for metric threads with large and small pitches for diameters of 1 - 600 mm are regulated by GOST 16093 - 81. This standard sets the maximum deviations of thread diameters in
Tolerances of threads with interference and with transition fits
The landings in question serve mainly to connect the studs to the body parts, if screw or bolt-nut connections cannot be used. These landings are used in fasteners
Standard threads for general and special applications
Table 9 shows the names of standard general-purpose threads, the most widely used in machine and instrument making, and gives examples of their designation in the drawings. To the most
Kinematic transmission accuracy
To ensure kinematic accuracy, standards are provided that limit the kinematic error of the transmission and the kinematic error of the wheel. kinematic
Transmission smoothness
This transmission characteristic is determined by parameters, the errors of which repeatedly (cyclically) appear per revolution of the gear and also form part of the kinematic error
Gear contact
To increase the wear resistance and durability of gears, it is necessary that the completeness of contact of the mating side surfaces of the gear teeth be the greatest. With incomplete and unequal
Side clearance
To eliminate possible jamming when the gear is heated, to ensure the conditions for the flow of lubricant and limit the backlash when reversing the reference and dividing real gears
Designation of wheel and gear accuracy
The accuracy of the manufacture of gears and gears is set by the degree of accuracy, and the requirements for the side clearance are set by the type of conjugation according to the standards of the side clearance. Symbol examples:
The choice of the degree of accuracy and controlled parameters of gears
The degree of accuracy of the wheels and gears is set depending on the requirements for kinematic accuracy, smoothness, transmitted power, as well as peripheral speed of the wheels. When choosing the degree of accuracy
Tolerances for bevel and hypoid gears
The principles of building a tolerance system for bevel gears (GOST 1758 - 81) and hypoid gears (GOST 9368 - 81) are similar to the principles for building a system for spur gears
Tolerances of worm gears
For worm cylindrical gears, GOST 3675 - 81 establishes 12 degrees of accuracy: 1, 2,. . ., 12 (in descending order of accuracy). For worms, worm wheels and worm gears
Tolerances and Fits for Straight-Tooth Joints
According to GOST 1139 - 80, tolerances are established for connections with centering on the inner d and outer D diameters, as well as on the sides of the teeth b. Since the view is centered
Tolerances and fits of splines with involute tooth profile
Nominal dimensions of involute spline connections (Figure 58), nominal dimensions by rollers (Figure 59) and common normal lengths for individual measurements of splined shafts and bushings should
Accuracy control of splines
Spline connections are controlled by complex through gauges (Figure 61) and element-by-element non-through gauges.
A method for calculating dimensional chains that ensures complete interchangeability
To ensure complete interchangeability, dimensional chains are calculated using the maximum-minimum method, in which the tolerance of the closing size is determined by arithmetic addition of the tolerances.
Theoretical and probabilistic method for calculating dimensional chains
When calculating dimensional chains by the maximum-minimum method, it was assumed that during processing or assembly, a simultaneous combination of the largest increasing and smallest decreasing sizes is possible.
Group interchangeability method in selective assembly
The essence of the method of group interchangeability lies in the manufacture of parts with relatively wide technologically feasible tolerances, selected from the relevant standards, grade
Adjustment and fit method
Regulation method. The regulation method is understood as the calculation of dimensional chains, in which the required accuracy of the initial (closing) link is achieved by a deliberate change
Calculation of flat and spatial dimensional chains
Flat and spatial dimensional chains are calculated using the same methods as linear ones. It is only necessary to bring them to the form of linear dimensional chains. This is achieved by designing
Historical foundations for the development of standardization
Man has been engaged in standardization since ancient times. For example, writing is at least 6,000 years old and originated according to the latest finds in Sumer or Egypt.
Legal basis for standardization
The legal basis for standardization in the Russian Federation is established by The federal law"On technical regulation" of December 27, 2002. It is mandatory for all state
Principles of technical regulation
At present, the following principles have been established: 1) the application of uniform rules for establishing requirements for products or for related design processes (including surveys), production
Objectives of technical regulations
The Law on Technical Regulation establishes a new document – the technical regulation. Technical regulation - a document that is adopted by an international treaty of Russia
Types of technical regulations
AT Russian Federation two types of technical regulations are applied: - general technical regulations; - special technical regulations. General technical regulations ra
The concept of standardization
The content of standardization terms has come a long evolutionary path. The clarification of this term took place in parallel with the development of standardization itself and reflected the level of its development on the p
Goals of standardization
Standardization is carried out in order to: 1) Increase the level of security: - life and health of citizens; - property of individuals and legal entities; - state
Object, aspect and area of standardization. Levels of standardization
The object of standardization is a specific product, service, manufacturing process(work), or groups of homogeneous products, services, processes for which requirements are being developed
Principles and functions of standardization
The main principles of standardization in the Russian Federation, which ensure the achievement of the goals and objectives of its development, are: 1) the voluntary application of documents in the field of standardization
International standardization
International standardization (IS) is an activity in which two or more sovereign states take part. MS has a prominent role in deepening world economic cooperation, in m
A set of standards of the national standardization system
To implement the Federal Law “On Technical Regulation”, since 2005, 9 national standards of the “Standardization of the Russian Federation” complex have been in force, which replaced the “State Standardization System” complex. it
The structure of standardization bodies and services
The national body for standardization is the Federal Agency for Technical Regulation and Metrology (Rostekhregulirovanie), which replaced the State Standard. It obeys directly
Normative documents on standardization
Normative documents on standardization (ND) - documents containing rules, general principles for the object of standardization and are available to a wide range of users. ND includes: 1)
Categories of standards. Standard designations
Standardization categories are distinguished by the level at which standards are accepted and approved. Four categories are established: 1) international; 2) intergo
Types of standards
Depending on the object and aspect of standardization, GOST R 1.0 establishes the following types of standards: 1) fundamental standards; 2) product standards;
State control over compliance with the requirements of technical regulations and standards
State control is exercised officials the state control body of the Russian Federation for compliance with the requirements of TR regarding the stage of product circulation. Bodies of state control of the region
Organization Standards (STO)
The organization and procedure for the development of SRT is contained in GOST R 1.4 - 2004. Organization - a group of employees and the necessary funds with the distribution of responsibilities of authority and mutual
The need for preferred numbers (P.N.)
The introduction of the IF is caused by the following considerations. The use of a frequency converter allows the best possible harmonization of the parameters and dimensions of a single product with all associated
Series based on arithmetic progression
Most often, the IF series are built on the basis of a geometric progression, less often on the basis of an arithmetic progression. In addition, there are varieties of rows built on the basis of the "golden"
Series based on geometric progression
The long practice of standardization has shown that the most convenient are the series built on the basis of a geometric progression, since this results in the same relative difference between
Properties of series of preferred numbers
IF series have the properties of a geometric progression. The IF series are not limited in both directions, while numbers less than 1.0 and more than 10 are obtained by dividing or multiplying by 10, 100, etc.
Limited, sample, composite and approximate series
Limited rows. If it is necessary to limit the main and additional series, their designations indicate the limit members, which are always included in the limited series. Example. R10(
The concept and types of unification
During unification, the minimum allowable but sufficient number of types, types, standard sizes, products, assembly units and parts that have high rates quality
Unification level indicators
The level of unification of products is understood as their saturation with unified constituent elements; parts, modules, nodes. The main quantitative indicators of the level of product unification
Determination of the indicator of the level of unification
The assessment of the level of unification is based on the correction of the following formula:
History of certification development
"Certificate" in Latin means "done right". Although the term "certification" has become known in Everyday life and commercial practice
Terms and definitions in the field of conformity assessment
Conformity assessment - direct or indirect determination of compliance with the requirements for an object. A typical example of activity for assessing
Goals, principles and objects of conformity assessment
Conformity assessment is carried out in order to: - certify the conformity of products, design processes (including surveys), production, construction, installation
The role of certification in improving product quality
Radically improving the quality of products in modern conditions is one of the key economic and political tasks. That is why the set of the same
Product certification schemes for compliance with the requirements of technical regulations
Certification scheme - a certain set of actions, officially accepted as evidence of product compliance with specified requirements.
Schemes for declaring conformity for compliance with the requirements of technical regulations
Table 17 - Schemes for declaring conformity for compliance with the requirements of technical regulations Designation of the scheme Content of the scheme and its use
Service certification schemes
Table 18 - Service certification schemes Scheme No. Assessment of the quality of services provided Verification (testing) of the results of services
Compliance Schemes
Table 19 - Product certification schemes Scheme number Tests in accredited testing laboratories and other methods of proof
Mandatory confirmation of compliance
Mandatory confirmation of conformity can be carried out only in cases established by technical regulations and solely for compliance with their requirements. Wherein
Declaration of Conformity
The Federal Law "On Technical Regulation" sets out the conditions under which a declaration of conformity can be adopted. First of all, this form of confirmation of conformity d
Mandatory certification
Mandatory certification in accordance with the Federal Law "On Technical Regulation" is carried out by an accredited certification body on the basis of an agreement with the applicant.
Voluntary confirmation of compliance
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 an agreement
Certification systems
A certification system is understood as a set of certification participants operating in a certain area according to the rules defined in the system. The concept of "certification system" in
Certification procedure
Certification of products passes through the following main stages: 1) Submission of an application for certification; 2) Consideration and adoption of a decision on the application; 3) Selection, id
Certification Bodies
Certification Body - entity or an individual entrepreneur duly accredited to perform certification work.
Test laboratories
Testing laboratory - a laboratory that conducts tests (certain types of tests) of certain products. During the ser
Accreditation of certification bodies and testing laboratories
According to the definition given in the Federal Law "On Technical Regulation", accreditation is "the official recognition by the accreditation body of the competence of a physical
Service certification
Certification is carried out by accredited service certification bodies within their scope of accreditation. Certification examines the characteristics of services and uses methods
Quality systems certification
AT last years There is a rapidly growing number of companies worldwide that have certified their quality systems to the ISO 9000 series of standards.
The measurement of physical quantities consists in comparing any quantity with a homogeneous quantity, taken as a unit. In metrology, the term "measurement" is used, which means finding the value of a physical quantity empirically using special technical means.
Measurements performed with the help of special technical means are called instrumental. The simplest example of such measurements is determining the size of a part with a ruler with divisions, that is, comparing the size of a part with a unit of length stored by a ruler.
Derived from the term "measurement" is the term "measure", widely used in practice. There are terms "measure", "measure", "measure", but their use in metrology is unacceptable.
To streamline the measurement activity, measurements are classified according to the following criteria:
General methods of obtaining results - direct, indirect, compatible, cumulative;
The number of measurements in a series - single and multiple;
Metrological purpose - technical, metrological;
Characteristics of accuracy - equal and unequal;
Relation to the change in the measured value - statistical and dynamic;
Expression of the measurement result - absolute and relative;
Direct measurements - measurements in which the desired value of a quantity is found directly from experimental data (measurements of mass on a balance, temperature of thermometers, length using linear measures). In direct measurements, the object of study is brought into interaction with measuring instruments and, according to the testimony of the latter, the value of the measured quantity is counted. Sometimes the instrument readings are multiplied by a coefficient, appropriate corrections are introduced, etc. These measurements can be written as an equation: X \u003d C X P,
where X is the value of the measured quantity in units accepted for it;
C is the price of a scale division or a single reading of a digital reading device in units of the measured value;
X P - reading on the indicator device in scale divisions.
Indirect measurements - measurements, at which the desired value is found on the basis of a known relationship between this value and the values \u200b\u200bobtained by direct measurements (determination of the density of a homogeneous body by its mass and geometric dimensions, the electrical resistivity of the conductor by its resistance, length and cross-sectional area). In the general case, this dependence can be represented as a function X = (X1,X2,....,Xn), in which the value of the arguments X1, X2, ...., Xn is found as a result of direct, and sometimes indirect, joint or cumulative measurements .
For example, the density of a homogeneous solid bodyρ is found as the ratio of the mass m to its volume V, and the mass and volume of the body are measured directly: ρ=m/V.
To improve the accuracy of measurements of density ρ, mass m and volume V are measured repeatedly. In this case, the density of the body
ρ = m/V , m is the result of body weight measurement, m = 1/n Σ m i ;
V=ΣVi/n - the result of measuring the volume of the body Π.
Aggregate measurements - measurements of several homogeneous quantities, in which the desired value of the quantities is found by solving a system of equations obtained by direct measurements of various combinations of these quantities (measurements in which the mass of individual weights of the set are found from the known mass of one of them and from the results of direct comparisons of the masses of various combinations of weights ).
Joint measurements - simultaneous measurements of two or more opposite quantities to find the relationship between them (simultaneously measuring the increment in the length of the sample depending on changes in its temperature and determining the coefficient of linear expansion).
Joint and cumulative measurements are very close in terms of the methods of finding the desired values of the measured quantities. The difference lies in the fact that with cumulative measurements, several quantities of the same name are simultaneously measured, and with joint measurements, opposite ones. The values of the measured quantities x1, ..., xn are determined on the basis of the cumulative equations;
F1 (X1, ..., Xm, X11, ... , X1n);
F2 (X1, ..., Xm, X21, ... , X1n);
Fn (X1, ..., Xm, Xk1, ... , Xkn),
where X11, X21, ……………..Xk n - values measured by direct methods.
Joint measurements are based on well-known equations that reflect the relationships existing in nature between the properties of objects, i.e. between quantities.
Absolute measurements are measurements based on direct measurements of one or more basic quantities and the use of physical constants.
Relative measurements - obtaining the ratio of a quantity to a quantity of the same name, which plays the role of a unit, or a change in a quantity in relation to a quantity of the same name, taken as the initial one.
Single measurement- measurement, performed once (measurement of a specific time by the clock).
Multiple measurements - measurements of the same physical quantity, the result of which is obtained from several consecutive measurements. Typically, multiple measurements are those that are made more than three times.
Technical measurements - measurements performed using working measuring instruments in order to control and manage scientific experiments, control product parameters, etc. (measurement of air pressure in the automobile chamber).
Metrological measurements - measurements with the help of standards and exemplary measuring instruments with the aim of innovating units of physical quantities or transferring their sizes to working measuring instruments.
Equal-precision measurements are a series of measurements of a quantity made by measuring instruments of the same accuracy under the same conditions.
Unequal measurements - a series of measurements of any value, made with different accuracy with measuring instruments and under different conditions.
Static measurements - measurements of a physical quantity, taken in accordance with a specific measurement task as unchanged over the measurement time (measuring the size of a part at normal temperature).
Dynamic measurements - measurements of a physical quantity, the size of which changes over time (measurements of the distance to ground level from a descending aircraft).
Measuring instruments
Measuring instruments are technical means used in measurements and having normalized metrological properties. The correct determination of the value of the measured quantity in the process of its measurement depends on the measuring instruments. Measuring instruments include: measures: measuring instruments, measuring installations, measuring systems.
Measure - a measuring instrument designed to reproduce a physical quantity of a given size (a weight is a measure of mass, a generator is a measure of the frequency of electrical oscillations). Measures, in turn, are divided into single-valued and multi-valued.
Unambiguous measure - measure, reproducing a physical quantity of the same size (plane-parallel end measure of length, normal element, capacitor of constant capacitance),
multi-valued measure - a measure that reproduces a series of physical quantities of the same name of various sizes (ruler: in millimeter divisions, a capacitor of variable capacitance).
A set of measures is a specially selected set of measures used not only individually, but also in various combinations in order to reproduce a number of similarly named quantities of various sizes (a set of weights, a set of plane-parallel end measures of length).
A measuring device is a measuring device designed to generate a signal of measuring information in a form accessible to direct perception by an observer. The results of measurements are issued by the reading devices of the instruments, which can be scale, digital and recording.
Scale reading devices consist of a scale, which is a set of marks and numbers representing a series of successive values of the measured value, and a pointer (pointer, electron beam, and others) associated with the moving system of the device.
Scale marks with numerical values represented are called numerical scale marks. The main characteristics of the scale are the length of the scale division, which is expressed by the distance between the axes of two adjacent scale strokes, and the scale division value, which represents the value of the measured quantity that causes the pointer to move one division.
It is also customary to single out the concepts: range of measurements and range of indications.
The measurement range is part of the range of indications for which the limits of permissible errors of measuring instruments are normalized. Least and greatest value The measurement range is called the lower and upper limits of the measurements, respectively.
The value of a quantity determined by the reading device of the measuring instrument and expressed in the accepted units of this quantity is called the indication of the measuring instrument.
The measured value is determined either by multiplying the number of scale divisions by the scale division value or by multiplying the numerical value read on the scale by the scale constant.
Currently, either mechanical or light digital readout devices are widely used.
Recording reading devices consist of a writing or printing mechanism and a tape. The simplest writing device is a pen filled with ink, which fixes the measurement result on a paper tape. In more complex devices, the recording of the measurement result can be carried out by a light or electron beam, the movement of which depends on the values of the measured quantities.
Lecture 3. MEASUREMENTS OF PHYSICAL QUANTITIES
3.1 Measurements of physical quantities and their classification
3.2 Principles, measurement methods
3.3. Measurement technique
Measurements of physical quantities and their classification
The reliability of measurement information is the basis for analysis, forecasting, planning and production management in general, it contributes to improving the efficiency of accounting for raw materials, finished products and energy costs, as well as improving the quality of finished products.
Measurement- a set of operations performed to determine the quantitative value of the quantity;
Measurement of a physical quantity - a set of operations on the use of a technical means that stores a unit of a physical quantity, providing a ratio of the measured quantity with its unit and obtaining the value of this quantity.
Measurement object- a real physical object, the properties of which are characterized by one or more measured PV.
measuring technology- a set of technical means used to perform measurements.
The main consumer of measuring equipment is industry. here, measuring equipment is an integral part of the technological process, as it is used to obtain information about technological modes that determine the course of processes.
technological measurements- a set of measuring devices and measurement methods used in technological processes.
Measurement object– body (physical system, process, phenomenon, etc.), which is characterized by one or more measurable or measurable physical quantities.
Measurement quality- this is a set of properties that determine the compliance of the means, method, methodology, measurement conditions and the state of unity of measurements with the requirements of the measurement task.
Measurements are classified according to the following criteria:
3.1.1 According to the dependence of the measured value on time into static and dynamic ;
Static Measurements– measurement of a physical quantity taken in accordance with the measurement task as a constant over the measurement time (for example, measuring the size of a part at normal temperature).
Dynamic measurements– measurements of a physical quantity, the size of which changes over time (for example, measuring mass fraction water in the product during drying).
3.1.2 By way of obtaining results into direct, indirect, cumulative, joint;
Direct measurement- a measurement in which the desired value of a physical quantity is found directly from experimental data. In the process of direct measurement, the object of measurement is brought into interaction with the measuring instrument and, according to the indications of the latter, the value of the measured quantity is counted. An example of direct measurements are measurements of length with a ruler, weight with a balance, temperature with a glass thermometer and active acidity with a pH meter, etc.
Direct measurements include measurements of the vast majority of parameters of the chemical-technological process.
Indirect measurement- a measurement in which the desired value of a quantity is found on the basis of a known relationship between this quantity and the quantities obtained by direct measurement.
Indirect measurements are used in two cases:
· there is no measuring tool for direct measurements;
Direct measurements are not accurate enough.
When conducting chemical analyzes of the composition and properties of nutrients, indirect measurements are widely used. An example of indirect measurements are measurements of the density of a homogeneous body by its mass and volume; determination of the mass fraction of water in fish products by drying at a temperature of 105 about C, the essence of which is to dry the product to constant weight and determine the mass fraction of water according to the formula:
where M 1 is the weight of the bottle with a sample before drying, g; M 2 is the weight of the bottle with a sample after drying, g; M is the mass of the sample.
Cumulative measurements - measurements of several homogeneous quantities, in which the desired values of quantities are found by solving a system of equations obtained by direct measurements of various combinations of these quantities (measurements in which the mass of individual weights of the set is found from the known mass of one of them and from the results of direct comparisons of the masses of various combinations of weights).
Joint measurements - simultaneous measurements of two or more dissimilar quantities to find the relationship between them (for example, simultaneous measurements of the increment in the length of the sample depending on changes in its temperature and the determination of the coefficient of linear expansion by the formula k = l / (l Dt)).
Joint measurements practically do not differ from indirect ones.
3.1.3. In connection with the object for contact and non-contact , at which the sensitive element of the device is brought or not brought into contact with the object of measurement.
3.1.4. According to the terms of accuracy into equal and unequal.
Equivalent measurements - a series of measurements of some quantity, made by measuring instruments of the same accuracy under the same conditions.
Unequal measurements- a series of measurements of a certain quantity, performed by measuring instruments of different accuracy and under different conditions. For example, the mass fraction of water in dried fish was determined by two methods: drying at a temperature of 130 about C and on the HF device at a temperature of 150 about C, the permissible error in the first case is +1%, in the second - +0.5%.
3.1.5 By the number of measurements in a series of measurements for single and multiple use.
Single measurement– measurement performed once (measurement of a specific time by clock).
Multiple measurement- measurement of a physical quantity of the same size, the result of which is obtained from several consecutive measurements, i.e. consisting of a number of single measurements. Typically, multiple measurements are those that produce more than three times. The result of multiple measurements is usually taken as the arithmetic mean of individual measurements.
3.1.6. For metrological purposes for technical, metrological;
Technical Dimension- a measurement made with a working measuring instrument for the purpose of monitoring and managing scientific experiments, monitoring the parameters of products, etc. (measurement of temperature in a smoking oven, determination of the mass fraction of fat in fish).
Metrological measurement- a measurement made using a standard and exemplary measuring instruments in order to introduce a new unit of physical quantity or transfer its size to working measuring instruments.
3.1.7 By expression of measurement result into absolute and relative;
Absolute measurement– measurement based on direct measurements of one or more basic quantities and on the use of physical constants. For example, the measurement of gravity is based on the measurement of the main quantity - mass (m) and the use of the physical constant g: F = mg.
Relative measurement- a measurement performed in order to obtain the ratio of a quantity to the value of the same name, which plays the role of a unit, or to measure the value in relation to the value of the same name, taken as the initial one. For example, measuring the relative humidity of the air.
3.1.8. According to the established sets of measured values on the electrical ( current, voltage, power) , mechanical ( mass, number of products, efforts); , heat power(temperature, pressure); , physical(density, viscosity, turbidity); chemical(compound, Chemical properties, concentration) , radio engineering etc.
An analysis of the state of measurements in the food industry made it possible to establish the qualitative and quantitative composition of the measuring equipment fleet, which is characterized by the following ratio (%):
- thermotechnical measurements - 50.7;
- mechanical measurements - 30.4;
– electric power – 12.1;
- physical and chemical measurements - 6.2;
– measurements of time and frequency – 0.6.
Principles and methods of measurement
Measuring principle- the physical phenomenon or effect underlying the measurements. For example, temperature measurement with a liquid thermometer is based on an increase in the volume of a liquid as the temperature rises.
Measurement methodth- reception or set of methods for comparing the measured physical quantity with its unit in accordance with the principles of measurement being implemented.
The classification of measuring methods is shown in Figure 3.1.
Fig 3.1. Classification of measurement methods
Direct evaluation method- a measurement method in which the value of the measured quantity is determined directly by the reading device of a direct-acting measuring device (with a reading on a scale or on a vernier scale - an auxiliary scale on which the divisions of the main scale are counted). For example, counting by clock, ruler.
Measure comparison method- a method of measurement in which the quantity being measured is compared with the quantity reproducible by the measure.
Measure– MI designed to reproduce PV of a given size
The comparison method is zero, differential, substitution.
Zero method- a kind of differential method, in which the resulting effect of the impact of quantities on the comparison device is brought to zero (pan scales). In this case, the value of the measured quantity is equal to the value that the measure reproduces.
At differential method the measured value x is compared directly or indirectly with the value x m of the reproducible measure. The value of x is judged by the difference Δx = x - x m measured by the instrument of the simultaneously measured values x and xm and by the known value xm, reproducible by the measure. Then
x = x m + Δx
substitution method- a method in which the desired value is replaced by a measure with a known value.
Depending on the contact with the measured value, the methods are divided into contact and non-contact , at which the sensitive element of the device is brought or not brought into contact with the object of measurement. An example of a contact measurement is the measurement of the product temperature with a thermometer, and a non-contact measurement is the measurement of the temperature in a blast furnace with a pyrometer.
Depending on the principle underlying the measurement, methods are divided into physical, chemical, physico-chemical, microbiological, biological .
physical method– the method is based on the registration of an analytical signal that fixes a certain property as a result of a physical process.
By using physical method determine the physical properties of aquatic organisms (mass, length, color) and many process control parameters (temperature, pressure, time, etc.) During the study, various measuring instruments are used. This method is the most objective and progressive.
Advantages - quick determination, accuracy of the result
Disadvantages - the inability to determine many indicators, mainly analytical
chemical method– is based on the fixation of an analytical signal arising as a result of chemical reaction, is used to assess the composition and properties of the product. For example: titrometry (determination of salinity, gravimetry - determination of the content of sulfates in table salt).
Advantages: the most accurate and objective.
Disadvantages: the duration of the analysis, requires the preparation of reagents, a large number of dishes.
Physico-chemical method- is based on the registration of a signal that occurs as a result of a chemical reaction, but which is fixed in the form of a measurement of some physical property. Is currently the most progressive. Physico-chemical methods are divided into:
O optical methods- use the connection between optical properties system and its composition.
- calorimetric If - based on measuring the absorption of electromagnetic energy in a narrow range of light lengths (determination of the amount of phenols, vitamin content, etc.).
- refractometric - based on the measurement of the refractive index of the solution (determination of the dry matter content in tomato).
- potentiometric- based on the determination of the equilibrium potential (measurement of EMF) and finding the relationship between its value and the potential-determining component of the solution (Determination of the pH of the solution)
- polarographic– based on determining the dependence of the current strength on the increase in voltage at the electrode of a cell immersed in a solution (determination of heavy metals)
- conductometric- based on the determination of the electrical conductivity of electrolyte solutions (determination of heavy metals, the concentration of salt in the solution).
- combined methods- based on the separation of complex mixtures into individual components and their quantitative determination, there are: chromatographic (thin-layer - determination of the fatty acid composition; gas-liquid - determination of the amino acid composition, pesticides, adsorption, ion-exchange).