ACCURACY OF MEASUREMENTS

ACCURACY OF MEASUREMENTS

The characteristic of the quality of measurements, reflecting the degree of closeness of the measurement results to the true value of the measured value. The less the measurement result deviates from the true value of the quantity, i.e., the smaller its error, the higher the T. and., Regardless of whether the error is systematic, random, or contains both components (see MEASUREMENT ERRORS). Sometimes in quantity. estimates T. and. indicate an error, however, an error is the opposite of accuracy, and it is more logical as an estimate of T. and. indicate the reciprocal of rel. errors (without taking into account its sign). For example, if it relates. the error is ± 10-5, then it is equal to 105.

Physical encyclopedic dictionary. - M .: Soviet encyclopedia. Chief Editor A.M. Prokhorov. 1983 .

See what "MEASUREMENT ACCURACY" is in other dictionaries:

Accuracy of measurements- The quality of measurements, reflecting the proximity of their results to the true value of the measured quantity Source: GOST 24846 81: Soils. Methods for measuring deformations of the foundations of buildings and structures ...

accuracy of measurements- - [L.G. Sumenko. The English Russian Dictionary of Information Technology. M .: GP TsNIIS, 2003.] Subjects information Technology overall EN accuracy of measurements ...

Through the so-called measuring instruments constantly increases with the growth of science (Measurements; Units of measures are absolute systems). It now depends not only on the careful preparation of the instruments, but also on the finding of new measurement principles. So … Encyclopedic Dictionary of F.A. Brockhaus and I.A. Efron

accuracy of measurements- verification. to believe. the device is lying. see showing time ... Ideographic Dictionary of the Russian Language

GOST R EN 306-2011: Heat exchangers. Measurement and Measurement Accuracy in Power Determination- Terminology GOST R EN 306 2011: Heat exchangers. Measurement and measurement accuracy in determining power: 3.31 impact magnitude Definitions of the term from ... ... Dictionary-reference book of terms of normative and technical documentation

measurement accuracy- measurement accuracy One of the characteristics of the measurement quality, reflecting the proximity to zero of the measurement result error. Note. It is believed that the smaller the measurement error, the greater its accuracy. [RMG 29 99] Topics metrology, ... ... Technical translator's guide

accuracy- 3.1.1 accuracycloseness of the agreement between a measurement result and an accepted reference value Note The term "accuracy", when it refers to a series of measurements, includes a combination of random components and an overall systematic ... ... Dictionary-reference book of terms of normative and technical documentation

Means of measurement the degree of coincidence of the readings of the measuring device with the true value of the measured value. The smaller the difference, the more accurate the instrument is. The accuracy of a standard or measure is characterized by an error or degree ... ... Wikipedia

accuracy- The degree of closeness of the measurement result to the accepted reference value. Note. The term "accuracy", when it refers to a series of measurement (test) results, includes a combination of random components and an overall systematic ... ... Technical translator's guide

measuring instrument accuracy- accuracy A characteristic of the quality of a measuring instrument, reflecting the proximity of its error to zero. Note. It is believed that the smaller the error, the more accurate the measuring instrument. [RMG 29 99] Topics metrology, basic concepts Synonyms precision ... Technical translator's guide

Books

• Physical foundations of measurements in technologist. food and chemical industries. Study guide, Popov Gennady Vasilievich, Zemskov Yuri Petrovich, Kvashnin Boris Nikolaevich Series: Textbooks for universities. Special literature Publisher: Lan,
• Physical bases of measurements in technologies of food and chemical industries. Textbook, Popov Gennady Vasilievich, Zemskov Yuri Petrovich, Kvashnin Boris Nikolaevich, This manual provides brief theoretical information about the regularities of measurements, measuring systems, elements of the physical picture of the world, as well as the principles of measurements based on ... Series: Textbooks for universities. Special literature Publisher:

The accuracy of measurement of quantities is the ability to streamline the existence of a person and his environment. It would be impossible to imagine a life in which there would be no familiar and approved concepts of time, length or mass for all of us. However, in addition to the fact that they need to be able to identify them, it is equally important to learn how to determine and calculate distances and segments, weight, speed of movement of objects, the course of time intervals. Over a thousand-year history of existence, mankind has acquired a lot of priceless knowledge and has managed to systematize it into separate sciences.

Concepts and designations - basics of metrology

Metrology is a study that helps you understand the measurement of different quantities. It makes it possible to understand what a measure, unity and standardization of quantities is, defines concepts such as measurement accuracy, error, introduces a variety of measuring instruments and instruments.

The measurement process is associated with the determination of data regarding a particular quantity through experiments, as well as the subsequent correlation of the obtained values ​​with generally accepted standards and units. Thus, we can assume that the measurement accuracy directly depends on how close the data obtained as a result of the experiments are to the true values ​​of the quantity, which, in principle, cannot be disputed and are an axiom.

Absolute inaccuracy

Scientists argue that it is almost impossible to measure anything absolutely correctly. The fact is that there are too many factors influencing the process of determining the value, independent of human actions. In this regard, metrology admits the possibility of the existence of errors, which are inaccuracies obtained in the measurement process, as well as a kind of indicator that shows deviations from the generally accepted truth and norm.

The error can be systematic or random. It is practically impossible to exclude the first one during the experiment, because this is such a factor that will distort the result every time, but an accidental error can be the result of a gross error or inaccuracy of analytical activity.

It is also possible to reduce the probability of error by using more advanced methods and tools, minimizing the influence of external influences during the experimental determination of values. An elementary example of reducing errors can be considered the use of a clock, if time is measured not in hours and minutes, but in fractions of a second, which electronic stopwatches allow.

Measure seven times ...

The need to obtain absolutely accurate knowledge of the values ​​is due to high manufacturability modern world... If the first sample of furniture was a roughly knitted toilet seat, the details of which were cut out by eye, then current technologies help to create elements of the same stools with an error of up to a millimeter. Perhaps in Everyday life For humans, such microscopic values ​​are absolutely unimportant, but when the measurement accuracy concerns science, medicine, production, it becomes a decisive factor in the success of an enterprise.

If you look closely, then every person in the house has the simplest measuring instruments. Elementary examples of these are a building tape measure, a ruler, kitchen or floor scales, a steelyard, electricity, water, gas meters, various timers and clocks, thermometers and thermometers. By the example of the latter, one can once again demonstrate the methods and accuracy of measurement. So, the usual one installed in a room in order to determine the air temperature in a room has a scale with a division of ten degrees, while a mercury thermometer, designed to measure a person's body temperature, is divided into a tenth of a degree, which helps to reduce the likelihood of errors during the collection of a patient's anamnesis ...

What is length and how to measure it?

One of the most recognizable and definite dimensions is length. Probably, originally a person measured the distance with the help of steps, but now the units of measurement of distance are normalized. The world standard is a metric system where highest value measured in kilometers, conventionally divided into meters, centimeters and millimeters. There are also intermediate values ​​(decimeters, micrometers), but they are often used only in highly specialized areas.

In order to determine the length, it is necessary to select a specific segment that will have a beginning and an end (points A and B), and so the length is the value of the quantity the greatest distance on the plane between these points. To measure length, a variety of instruments have been created, from elementary ones, such as a centimeter and a ruler, to control and measuring equipment of a high degree of accuracy with a minimum error.

Household length measuring devices

Long distance to an ordinary person it is hardly necessary to measure, each of us knows approximately the length of our routes, such data can be clarified using a car speedometer, a sports-tourist pedometer, or even using a smartphone by downloading a special program into it.

Houses are more often used for construction and renovation. Construction tape is what any man has in the closet. It is a metal tape with a scale applied to one or both of its sides from 0 to 3, 5, 7.5, 30 meters with additional centimeter and millimeter divisions. An alternative to a simple tape measure can be with which you can calculate distances up to 250 m, in addition, measuring the length with it is easy to do even alone. There are also models that display the area and volume of a room.

Calipers

Measuring with a caliper will give the most accurate result. This is a device that is used in industry and provides an opportunity to find out the linear value of parts from 0.1 mm to 15 cm in size with a minimum error. To determine how close the scale is to the true value, you can use such comparative methods - comparison with an already tested instrument or with a finished part of a suitable size.

There are several types of this device, their principle of operation is similar, they differ in the length of the millimeter scale and the mechanism by which the measurement is actually made. A vernier caliper is the most difficult to work with, but this option makes it possible to minimize systematic errors. In an instrument with a dial or digital display, measurements are made electronically and if the instrument is of proper quality, then its results are obtained with a high degree of probability.

Complex technologies

Even more complex Computer Engineering- these are control and measuring devices used in industrial enterprises and organizations involved in the installation of power lines, laying television, telephone and Internet cables. This technique copes with several functions at once. The main task is to measure the length of the cable, however, along the way, the device can reveal errors in the operation of the wire, indicating the place of power outage, which significantly minimizes the money and time required to carry out repair work.

There are different classes of measuring instruments. The most elementary - manual settings with meters of cable length, more complex options able to calculate not only the length of the wires, but also measure wide rolls of fabrics, paper, different types of cords. In addition to the fact that their use is advisable on production lines, the introduction of such technology is spreading in warehouses and in large retail outlets.

How to embrace the immensity

Measuring time is also a complex and important task. V life situations few people pay attention to the fact that personal watches can be in a hurry or lag behind the generally accepted standard by a few minutes. but public organizations and enterprises cannot afford such liberty, and therefore they compare the time with indicators in government agencies, which, in turn, are guided by data obtained using satellites.

It should be noted that such a concept as exact time is rather arbitrary. The time zones into which the planet is divided are objective in nature and are directly dependent on state borders, and sometimes on the political will of the government of different countries.

Measurement- a set of operations for application technical means, storing the unit of quantity, providing finding the ratio of the measured quantity with its unit in explicit or implicit form and obtaining the value of this quantity. In general, metrology is the science of measurements, methods and means of ensuring their unity and ways to achieve the required accuracy.

Improvements in measurement accuracy have spurred the development of the sciences by providing more reliable and sensitive research tools. The efficiency of the performance of various functions depends on the accuracy of measuring instruments: errors in energy meters lead to uncertainty in electricity metering; inaccuracies in the weights lead to deception of buyers or to large volumes of unaccounted for goods.

Improving the measurement accuracy allows you to identify the shortcomings of technological processes and eliminate these shortcomings, which leads to an increase in product quality, savings in energy and heat resources, raw materials and materials.

Measurements can be classified according to their accuracy specification into:

Equal - a series of measurements of any quantity, performed by measuring instruments of the same accuracy and under the same conditions;

Unequal - a series of measurements of a quantity made by several measuring instruments of different accuracy and (or) under several different conditions.

TO different types measuring instruments have specific requirements: for example, laboratory instruments must have increased accuracy and sensitivity. High-precision SI are, for example, standards. The standard of a unit of magnitude is a measuring instrument designed to reproduce and store a unit of magnitude, multiples or sub-multiples of its values ​​in order to transfer its size to other measuring instruments of a given value. Standards are high-precision measuring instruments and therefore are used for carrying out metrological measurements as a means of transmitting information about the size of a unit. The unit size is transmitted "from top to bottom" from more accurate measuring instruments to less accurate "along the chain": primary standard (secondary standard (working standard of the 0th category (working standard of the 1st category ... (working measuring instrument. Metrological properties of measuring instruments - these are properties that affect the measurement result and its error. Indicators of metrological properties are their quantitative characteristics and are called metrological characteristics. All metrological properties of measuring instruments can be divided into two groups:

Properties that determine the field of application of SI

Properties that determine the quality of the measurement. These properties include accuracy, repeatability, and reproducibility.

The most widely used in metrological practice is the property of measurement accuracy, which is determined by the error. Measurement error - the difference between the measurement result and the true value of the measured value.

Accuracy of SI measurements - the quality of measurements, reflecting the proximity of their results to the real (true) value of the measured quantity.

Accuracy is determined by indicators of absolute and relative error.

The absolute error is determined by the formula: Хп = Хп - Х0, where: Хп - the error of the verified measuring instrument; Xn - the value of the same quantity, found with the help of the verified SI; X0 is the SI value taken as the basis for comparison, i.e. real value.

However, to a greater extent, the accuracy of measuring instruments is characterized by the relative error, i.e. expressed as a percentage, the ratio of the absolute error to the actual value of the quantity measured or reproduced by the SI data.

The standards standardize the accuracy characteristics associated with other errors:

Systematic error is a component of the measurement result error that remains constant or regularly changes during repeated measurements of the same value. Such an error may appear if the center of gravity of the SI is shifted or the SI is not installed on a horizontal surface.

Random error - a component of the error of the measurement result, changing randomly in a series of repeated measurements of the same size, quantities with the same care. Such errors are not natural, but are inevitable and present in the measurement results.

The measurement error should not exceed the established limits, which are specified in the technical documentation for the device or in the standards for control methods (tests, measurements, analysis).

To exclude significant errors, regular verification of measuring instruments is carried out, which includes a set of operations performed by the bodies of the state metrological service or other authorized bodies in order to determine and confirm the compliance of the measuring instrument with the established technical requirements.

In everyday industrial practice they widely use a generalized characteristic - the accuracy class.

Accuracy class of measuring instruments is a generalized characteristic expressed by the limits of permissible errors, as well as other characteristics that affect the accuracy. Accuracy classes of a specific type of measuring instrument are established in regulatory documents. At the same time, for each accuracy class, specific requirements for metrological characteristics are established, in aggregate, reflecting the level of accuracy of the measuring instrument of this class. The accuracy class allows you to judge the extent to which the measurement error of this class is. It is important to know when choosing a measuring instrument, depending on the specified measurement accuracy.

Accuracy classes are designated as follows:

If the limits of the permissible basic error are expressed in the form of an absolute SI error, then the accuracy class is denoted capital letters Roman alphabet. Accuracy classes that correspond to smaller limits of permissible errors are assigned letters that are closer to the beginning of the alphabet.

For SI, the limits of the permissible basic error of which are usually expressed in the form of a relative error, are denoted by numbers that are equal to these limits, expressed as a percentage.

The designations of the accuracy class are applied to the dials, shields and cases of the SI, they are given in the regulatory documents. Instruments with multiple measuring ranges of the same physical quantity or those intended for measuring different physical quantities can be assigned different accuracy classes for each range or for each measured quantity.

Accuracy classes are assigned during the development of measuring instruments based on the results of acceptance tests. Due to the fact that during operation their metrological characteristics usually deteriorate, it is allowed to lower the accuracy class based on the verification results.

When preparing and conducting high-precision measurements in metrological practice, the influence of the measurement object, subject, measurement method, measuring instrument, measurement conditions is taken into account. So, the object must be comprehensively studied; the element of subjectivity in the measurement results should be minimized; take into account factors and conditions that can falsify the measurement results. Therefore, it is necessary to follow the measurement procedure in order to obtain results with a minimum error. Such techniques are set out in the law of the Russian Federation “On ensuring the uniformity of measurements. And in 1997 GOST 8.563-96 “GSI. Measurement Techniques ".

In my daily work, I do not often have to deal with different measuring instruments. However, I will give some comparative examples in which the accuracy can be judged by the sensitivity threshold. In many modern grocery stores now installed electronic scales, which are a working measuring instrument. The range of such weights is from 0 to 10 kg, and the division price (so to speak for electronic version scales) or the sensitivity threshold is 1 gram. Thus, the weighing accuracy is quite high and the error can be 0.001 kg. And not only the accuracy of measurement, but also the accuracy of settlements with customers - after all, its price depends on the weight of the product. Unfortunately, the accuracy class was not indicated on the case, and employees were confused with this question.

In grocery stores, you can often find ordinary scales on which they weigh with the help of weights, which are also a working measuring instrument. The first time I paid attention to such scales and saw (!) That in our store they stand on uneven surface... The fact is that a hollow ball filled with water is mounted in the body of the balance. If the scales are level, then the upper edge of the water (under the influence of physical laws) is parallel to the surface. In my case, this was clearly not observed. The scale range is from 0 to 5 kg, and the sensitivity threshold is 10 grams. From this it follows that such scales are less accurate than those described above - electronic, since the error can be 0.01 kg.

We have a scale for weighing vegetables at our warehouse. These scales have a range from 0 to 200 kg, so that any adult can easily weigh themselves on them. The sensitivity threshold is 200 grams and it is indicated on the dial. In addition, the dial indicates that the scales are manufactured by Suprema S.p.a., range 0-200 kg, e-d = 200 gr, serial number 122001/21 and individual number 91097. It also indicates the accuracy class - III - for similar measuring instruments related to professional equipment. The passport of these scales indicates that the accuracy classes for this product are set from I to III, probably in accordance with the regulatory documents in force in the manufacturing country.

And, finally, the steelyard, which has the lowest accuracy class and is a working measuring instrument. With this tool it is possible to carry out rather approximate weighing, because the graduation is 0.5 kg and the measurement error will be very significant. The steelyard range is from 0 to 7 kg. But even with such an inaccurate measuring instrument, the result depends on several factors. In this case, the measurement result directly depended on the person making the measurements. On re-weighing, the error was very high and depended on hand tremors and how accurately the balance was upright. 1

In power supply systems, current is measured ( I), voltage (U), active and reactive power (P,), electricity, active, reactive and impedance (P, Q), frequency ( f), power factor (cosφ); when supplying power, measure the temperature (Ө), pressure ( R

In operating conditions, direct assessment methods are usually used for measuring electrical quantities and zero for non-electrical quantities.

Electrical quantities are measured with electrical measuring instruments.

Electrical measuring instrument is called a device designed to measure an electrical quantity, for example, voltage, current, resistance, power, etc.

According to the principle of action and design features devices are: magnetoelectric, electromagnetic, electrodynamic, ferrodynamic, induction, vibration and others. Electrical measuring devices are also classified according to the degree of protection of the measuring mechanism from the influence of external magnetic and electric fields on the accuracy of its readings, according to the method of creating a counteracting moment, according to the nature of the scale, according to the design of the reading device, according to the position of the zero mark on the scale and other features.

On the scale of electrical measuring instruments, legend determining the system of the device, its technical characteristics.

Metering of electrical energy generated by generators or consumed by consumers is carried out by meters.

to measure electrical energy of alternating current, meters with a measuring mechanism of an induction system and electronic meters are mainly used. The deviation of the measurement result from the true value of the measured value is called the measurement error.

Measurement accuracy- measurement quality, reflecting the proximity of its results to the true value of the measured quantity. High measurement accuracy corresponds to small error.

Measuring instrument error- the difference between the readings of the device and the true value of the measured value.

Measurement result- the value of a quantity found by measuring it.

With a single measurement, the reading of the device is the result of the measurement, and with a multiple measurement, the measurement result is found by statistical processing of the results of each observation. According to the accuracy of the measurement results, they are divided into three types: full-time (precision), the result of which must have a minimum error; control and verification, the error of which should not exceed a certain specified value; technical, the result of which contains an error determined by the error of the measuring device. As a rule, accurate and control measurements require multiple observations.

According to the method of expressing the error of measuring instruments, they are divided into absolute, relative and reduced.

Absolute errorΔА is the difference between the reading of the device A and the actual value of the measured quantity A.

Relative error- the ratio of the absolute error ΔА to the value of the measured quantity А, expressed as a percentage:

.

Reduced error(in percent) - the ratio of the absolute error of the aircraft to the normalizing value:

.

For instruments with a zero mark at the edge or off the scale, the normalizing value is equal to the final value of the measuring range. For instruments with a double-sided scale, that is, with scale marks located on either side of zero, it is equal to the arithmetic sum of the end values ​​of the measuring range. For instruments with a logarithmic or hyperbolic scale, the normalizing value is equal to the length of the entire scale.

Table 1. Accuracy classes * measuring instruments

Means for measuring electrical quantities must meet the following basic requirements (PUE):

1) the accuracy class of measuring instruments must be at least 2.5;

2) the accuracy classes of measuring shunts, additional resistors, transformers and converters should be no worse than those given in table. 1.;

3) the measurement limits of instruments should be selected taking into account the possible largest long-term deviations of the measured values ​​from the nominal values.

The metering of active electrical energy should ensure the determination of the amount of energy: generated by the generators of the ES; consumed on p. n. and household needs(separately) ES and PS; released to consumers through lines extending from the ES tires directly to consumers; transferred to other power systems or received from them; released to consumers from the electrical network. In addition, metering of active electrical energy should provide the ability to: determine the flow of electrical energy into Electricity of the net different voltage classes of the power system; drawing up balances of electrical energy for self-supporting subdivisions of the power system; control over the observance by consumers of the modes of consumption and balance of electric energy set by them.

The metering of reactive electrical energy should provide the ability to determine the amount of reactive electrical energy received by the consumer from the power supply organization or transmitted to it, only if calculations or monitoring of compliance with the specified operating mode of compensating devices are made using these data.

Current measurement should be carried out in circuits of all voltages where it is necessary for systematic control technological process or equipment.

DC current measurement in circuits: DC generators and power converters; AB, chargers, rechargers and dischargers; excitation of SG, SK, as well as electric motors with adjustable excitation.

DC ammeters should have double-sided scales if current direction can be reversed.

In three-phase circuits, the current of one phase should generally be measured.

Measurement of the current of each phase should be carried out:

for TG 12 MW and more; for overhead lines with phase-by-phase control, lines with longitudinal compensation and lines for which the possibility of long-term operation in non-phase mode is provided; in justified cases, the measurement of the current of each phase of the overhead line 330 kV and above with three-phase control can be provided; for electric arc furnaces.

Voltage measurement should be done:

1. On DC and AC busbar sections that can be operated separately. installation of one device with switching to several measuring points is allowed. At the substation, the voltage is allowed to be measured only on the LV side, if the installation of the VT on the HV side is not required for other purposes.

2. In the circuits of DC and AC generators, SC, as well as in some cases in the circuits of special-purpose units.

With the automated start-up of generators or other units, the installation of instruments for continuous voltage measurement on them is not required.

3. In SM excitation circuits from 1 MW and more.

4. In the circuits of power converters, AB, chargers and rechargers.

5. In the circuits of the arc suppression coils.

In three-phase networks, as a rule, one phase-to-phase voltage is measured. In networks above 1 kV with an effectively grounded neutral, it is allowed to measure three phase-to-phase voltages to monitor the health of voltage circuits with one device (with switching).

Registration of the values ​​of one phase-to-phase voltage of the busbars of 110 kV and higher (or voltage deviations from the set value) of the ES and substations, according to the voltage at which the power system mode is carried out, should be performed.

Insulation monitoring... In AC networks above 1 kV with an isolated or grounded neutral through an arc suppression reactor, in AC networks up to 1 kV with an isolated neutral and in DC networks with insulated poles or with an isolated center point, as a rule, an automatic insulation check should be performed, acting to a signal when the insulation resistance of one of the phases (or pole) drops below the set value, followed by monitoring the voltage asymmetry using an indicating device (with switching). it is allowed to carry out insulation control by periodic voltage measurements in order to visual control voltage asymmetry.

Power measurement:

1. Generators active and re active power.

When installed on TGs of 100 MW and more, panel indicating devices, their accuracy class must be at least 1.0.

ES of 200 MW and more - total active power.

2. Capacitor banks 25 MVAr and more and SC of reactive power.

3. Transformers and power lines from. n. b kV and above ES, active power.

4. Step-up two-winding transformers ES - active and reactive. In the circuits of step-up three-winding transformers (or autotransformers using the LV winding), the active and reactive power should be measured from the MV and LV side. for a transformer operating in a unit with a generator, the power measurement from the NI side should be made in the generator circuit.

5. Step-down transformers 220 kV and above - active and reactive, 110-150 kV - active power.

In the circuits of step-down two-winding transformers, the power measurement should be made from the LV side, and in the circuits of three-winding step-down transformers - from the MV and LV side.

At substations 110-220 kV without switches on the side of the VP, power measurement is allowed not to be performed.

6. Lines 110 kV and above with two-way power supply, as well as bypass switches - active and reactive power.

7. On other elements of substation, where for periodic monitoring of network modes, measurements of active and reactive power flows are required, the possibility of connecting portable control devices should be provided.

registration must be carried out: active power of TG 60 MW and more; the total power of the power plant (200 MW and more).

Frequency measurement:

1. On each section of generator voltage busbars.

2. At each TG of a block power plant or nuclear power plant.

3. On each system (section) of HV ES buses.

4. At the nodes of the possible division of the power system into parts that work asynchronously.

Registration of the frequency or its deviation from the set value should be carried out: for power plants of 200 MW and more; for power plants of 6 MW and more, operating in isolation.

The absolute error of the recording frequency meters at the ES participating in power regulation should be no more than 0.1 Hz.

Synchronization measurements. For measurements with precise (manual or semi-automatic) synchronization, the following instruments should be provided: two voltmeters (or double voltmeter); two frequency meters (or double frequency meter); synchroscope.

Registration of electrical quantities in emergency modes. for automatic recording of emergency processes in the electrical part of power systems, automatic oscilloscopes should be provided. Arrangement of automatic oscilloscopes on objects, as well as the choice of recorded by them electrical parameters produced according to the instructions of the PUE.

To determine the places of damage on overhead lines of 110 kV and above with a length of more than 20 km, fixing devices should be provided.

Table 2. Characteristics of measuring instruments

Designation	Device type		Transformation	How is it used	Note
	Magnetoelectric (M) Logometer (M)				WITH- constant Coil currents
	Electromagnetic (E) Logometer (E)				Coil currents
	Electrodynamic (D) Logometer (D)				Coil currents Fixed coil current
	Ferrodians- Česky (D) Logometer (D)				Fixed coil current
	Induction (I) Logometer (I)				N - disk revolutions
	Electrostat- Česky (C) Thermal (T) Rectifier (V)

Modern industrial enterprises and housing and communal services are characterized by consumption different types energy: electricity, heat, gas, compressed air and others to monitor the mode of energy consumption, it is necessary to measure and record electrical and non-electrical quantities for the purpose of further information processing.

In the power supply, the current is measured ( I), voltage (U), active and reactive power (P, Q), electricity (W), active, reactive and impedance (R, X, Z), frequency ( f), power factor (cosφ); in power supply - temperature (Ө), pressure ( R), energy consumption (G), thermal energy(E), displacement (X), etc.

The range of instruments used in power supply to measure electrical and non-electrical quantities is very diverse both in measurement methods and in the complexity of the transducers. Along with the direct estimation method, zero and differential methods are often used to improve accuracy.

Given below a brief description of measuring devices according to the principle of operation.

Magnetoelectric devices have high sensitivity, low current consumption, poor overload capacity, high measurement accuracy. Ammeters and voltmeters have linear scales, and are often used as exemplary instruments, have low sensitivity to external magnetic fields.

Electromagnetic devices have low sensitivity, significant current consumption, good overload capacity, low measurement accuracy. The scales are not linear and are linearized in the upper part by a special design of the mechanism. More often used as a panel board technical devices, are simple and reliable in operation; sensitive to external magnetic fields.

Electrodynamic and ferrodynamic devices have low sensitivity, high current consumption, sensitivity to overloads, high accuracy. Ammeters and voltmeters have non-linear scales. An important positive feature is the same readings on constant and alternating currents, which allows you to verify them on a constant current. Most often they are used as laboratory instruments.

Induction system devices characterized by low sensitivity, significant current consumption, insensitivity to overloads. Mostly they serve as AC energy meters. Such devices are produced in one-, two- and three-element for operation in single-phase, three-phase three-wire, three-phase four-wire circuits. current and voltage transformers are used to expand the limits.

Electrostatic devices have low sensitivity, but are sensitive to overloads and are used to measure voltage on direct and alternating currents. Capacitive and resistive dividers are used to expand the limits.

Thermoelectric devices are characterized by low sensitivity, high current consumption, low overload capacity, low accuracy and non-linearity of the scale. However, their readings are independent of the current shape over a wide frequency range. high frequency current transformers are used to expand the limits of ammeters.

Rectifier devices characterized by high sensitivity, low current consumption, low overload capacity, linearity of the scale. The readings of the instruments depend on the shape of the current. They are used as ammeters and voltmeters.

Digital Electronic Measuring Instruments converts an analog input signal into a discrete one, representing it in digital form using a digital readout device (DPC) and can output information to an external device - display, digital printing. the advantages of digital measuring instruments (CII) are:

Automatic selection measuring range;

Automatic measurement process;

Displaying information in the code on external devices;

Presentation of measurement results with high accuracy.

Part one

Estimation of measurement errors. Recording and processing of results

In the exact sciences, in particular in physics, particular importance is attached to the problem of assessing the accuracy of measurements. That no measurement can be absolutely exact is a fact of general philosophical significance. Those. in the process of conducting an experiment, we always obtain an approximate value of a physical quantity, only approaching to one degree or another its true value.

Measurements, measurement accuracy indicators

Physics as one of natural sciences, explores our surroundings material world, using the physical research method, the most important component of which is the comparison of the obtained theoretical calculation data with experimental (measured) data.

The most important part of the process of teaching physics at the university is the implementation of laboratory work. In the process of their implementation, students measure various physical quantities.

When measured, physical quantities are expressed in the form of numbers that indicate how many times the measured quantity is greater or less than another quantity, the value of which is taken as a unit. Those. measurement means “ cognitive process, which consists in comparing a given physical quantity through a physical experiment with a known physical quantity taken as a unit of measurement. "

Measurements are performed using measures and measuring instruments.

Measure is called the real reproduction of a unit of measurement, fractional or multiple of its value (weight, measuring flask, magazines electrical resistances, containers, etc.).

Measuring instrument is called a measuring instrument that makes it possible to directly read the value of the measured quantity.

Regardless of the purpose and principle of operation, any measuring device can be characterized by four parameters:

1) Measurement limits indicate the range of the measurand available this instrument... For example, a vernier caliper measures linear dimensions in the range from 0 to 18 cm, and a milliammeter measures currents from -50 to +50 mA, etc. On some devices, you can change (switch) the measurement limits. Multi-range instruments can have several scales with different numbers of divisions. The counting should be carried out on the scale in which the number of divisions is a multiple of the upper limit of the device.

2) Value of division C determines how many units of measurement (or their fractions) are contained in one (smallest) division of the instrument scale. For example, the scale division of a micrometer C = 0.01 mm / division(or 10 μm / div), and for a voltmeter C = 2 In / cases etc. If the entire scale C is the same (uniform scale), then to determine the division value, you need the measurement limit of the device x nom divided by the number of instrument scale divisions N:

3) Sensitivity instrument α shows how many minimum scale divisions fall on the unit of the measured value or any part of it. From this definition it follows that the sensitivity of the device is the reciprocal of the division price: α = 1 / С. For example, the sensitivity of a micrometer can be estimated as α = 1 / 0.01 = 100 divisions / mm(or α = 0.1 div / μm), and for a voltmeter α = 1/2 = 0.5 cases / in etc.

4) Accuracy of the device characterizes the value of the absolute error, which is obtained during the measurement by this device.

The characteristic of the accuracy of the measuring instruments is the limiting error of the calibration Δ x deg... On the scale or in the passport of the device, the maximum absolute or relative error of the calibration is given, or the accuracy class is indicated, which determines the systematic error of the device.

In order of increasing accuracy, electrical measuring instruments are divided into eight classes: 4.0; 2.5; 1.5; 1.0; 0.5; 0.2; 0.1 and 0.05. The number denoting the accuracy class is applied to the scale of the device and shows the largest permissible value of the basic error as a percentage of the measurement limit x nom

Cl. accuracy = ε pr =.(2)

There are devices (mainly of high accuracy), the accuracy class of which determines the relative error of the device in relation to the measured value.

If there is no data on the accuracy class on the devices and in their passports and the formula for calculating the error is not indicated, then the instrumental error should be considered equal to half the scale division of the device.

Measurements are divided into straight and indirect... In direct measurements, the desired physical quantity is established directly from experience. In this case, the value of the measured value is read off on the scale of the device or the number and value of measures, weights, etc. are counted. Direct measurements are, for example, weighing on a scale, determining linear dimensions bodies of the correct shape using a caliper, determining the time by a stopwatch, etc.

In indirect measurements, the measured value is determined (calculated) from the results of direct measurements of other quantities that are associated with the measured value by a certain functional dependence. Examples of indirect measurements - determining the area of ​​a table by its length and width, body density by measuring body weight and volume, etc.

The quality of measurements is determined by their accuracy. In direct measurements, the accuracy of the experiments is established from the analysis of the accuracy of the method and instruments, as well as from the repeatability of the measurement results. The accuracy of indirect measurements depends both on the reliability of the data used for the calculation and on the structure of the formulas connecting these data with the desired value.

The accuracy of measurements is characterized by their error. Absolute measurement error called the difference between the experiment found x meas and the true value of the physical quantity x ist

To assess the accuracy of any measurements, the concept is also introduced relative error.

The relative measurement error is the ratio of the absolute measurement error to the true value of the measured value (can be expressed as a percentage).

As follows from (3) and (4), in order to find the absolute and relative measurement error, it is necessary to know not only the measured, but also the true value of the quantity of interest. But if the true value is known, then there is no need to measure. The purpose of measurements is always to find out the previously unknown value of a physical quantity and to find, if not its true value, then at least a value that differs little from it. Therefore, formulas (3) and (4), which determine the magnitude of the errors, are unsuitable for practice. Often instead of x ist use the arithmetic mean over multiple dimensions

where x i Is the result of a single measurement.