State budgetary educational institution of secondary vocational education "Salavat Industrial College"

ELECTRICAL MEASUREMENTS

METHODOLOGICAL INSTRUCTIONS

and tasks for performing CONTROL work for students studying by correspondence in the specialty

230113 Computer systems and complexes

Reviewed Approved

at a meeting of the cycle commission Deputy. director of

energy engineering disciplines educational work

protocol No.___from__________ _____________

Guidelines have been compiled

according to requirements

Federal State "______"______________

Educational standard for

secondary specialties

vocational education 230113

Computer systems and complexes

Chairman of the cycle commission

Reviewer:

Teacher at the Federal State Educational Institution of Secondary Professional Education "Salavat Industrial College"

Content

Introduction 4

	Passport work program academic discipline
	Structure and content of the academic discipline
	Scope of academic discipline and types academic work
	Thematic plan and content of the academic discipline "Electrical measurements"
	Conditions for the implementation of the academic discipline
	Monitoring and evaluation of the results of mastering the academic discipline
	Guidelines for studying educational material
	List of questions and tasks for the test
	List of questions for an exam or test

Introduction

The guidelines are intended for studying the academic discipline “Electrical engineering measurements” by correspondence students studying in the specialty 230113 Computer systems and complexes ( a basic level of preparation).

The purpose of the guidelines is the implementation of the Federal State Educational Standard in specialty 230113 Computer systems and complexes (basic level of training) through correspondence courses.

The guidelines have been compiled to the extent necessary to master the basics of electrical measurements, the principle of operation and the main characteristics of measuring instruments electrical quantities, as well as methods for measuring them.

As a result of studying this discipline, students must learn to choose the right measurement method, appropriate measuring and auxiliary equipment, acquire the skills of assembling electrical circuits, observing recordings and processing the results obtained, learn to check electrical measuring instruments, be able to draw up, read, assemble electrical circuit diagrams, and measure their parameters , choose the right measuring instruments for making measurements.

Carrying out measurements is one of the main means of obtaining objective knowledge about the world, and the accumulated experimental material is

a basis for generalizations and establishing the laws of its existence and

development. At the same time, carrying out measurements has an unconditional practical

value is largely based on measurement results and technical

development, and interaction between individual economic entities

activities. Among all measurements, electrical occupies a special place.

measurements due to the universality of electrical signals and available

possibilities for their processing and storage, often when measuring magnetic and

non-electrical quantities, the output signal of the converter is

namely an electrical signal.

The guidelines provide for the study of three sections:

Section 1. State system for ensuring unity –

general approaches to measurements in general are revealed and include information about units of measurement and errors that arise during measurements, as well as practical recommendations for processing measurement results, the relationship between the primary transducer and the measuring device is revealed, and general classification electrical measuring instruments

Section 2 Instruments and methods of electrical measurements - characterizes special technical means used in measuring current, resistance voltage, capacitance and inductance.

Section 3 Study of signal shapes - methods for studying signal shapes are revealed, as well as methods for measuring them, in addition, methods for measuring phase shift and methods for measuring frequency are revealed.

Methodological instructions provide for the implementation of laboratory work. Their goal is to more deeply assimilate and consolidate theoretical material, acquire skills in performing simple measurements of electrical quantities, and working with electrical measuring instruments. The number of laboratory works corresponds to the curriculum.

To successfully master this discipline, a student must be able to independently study educational literature and be able to use dictionaries

The distribution of teaching hours by sections and topics of the discipline, as well as the topics of practical work, can be changed and justified by the decision of the methodological commission, provided that the total amount of time for the discipline is maintained.

Review and practical classes are conducted during the examination session (as well as during the intersession period) in order to systematize, expand and consolidate the acquired knowledge and obtain answers to questions that arise.

At orientation classes, students are introduced to the discipline program, methods of working on the material and doing homework. test work.

Material presented for orientation and review classes, as well as a list of tasks to be performed practical classes are determined educational institution based on the relevant curriculum.

The curriculum provides for a test covering all sections of the curriculum. Options for the test work are compiled in relation to the current program for the discipline. Completing a home test determines the degree to which students have mastered the material being studied and the ability to apply the acquired knowledge when solving practical problems.

Familiarization with the thematic plan and methodological instructions by topic;

Compiling answers to self-control questions given after each topic.

Mastering the program material of the discipline consists of:

Independent study of educational material based on recommended literature;

Questions for self-control;

Carrying out practical work;

Carrying out tests.

When presenting the material, it is necessary to observe the unity of terminology and designations in accordance with current standards.

After studying the material, students complete a test.

The test is compiled in 20 versions and consists of two buildings: theoretical and practical. The theoretical part includes 4 questions. The practical part is solving one problem. The option number should be selected in accordance with the number number on the list in the training journal.

The test is completed in a separate squared notebook, the conditions of the tasks are completely rewritten;

As a result of mastering the academic discipline, the student should be able to:

Draw up circuit diagrams for connecting electrical measuring instruments;

Select means of electrical measurements;

Measure electrical quantities with a given accuracy;

Determine the value of the measured quantity and measurement accuracy indicators;

Use funds computer technology for processing and analyzing measurement results.

As a result of mastering the academic discipline, the student should know:

Basic methods and means of measuring electrical quantities;

Design, principle of operation, purpose of electrical measuring instruments;

The influence of measuring instruments on the accuracy of measurements;

Characteristics of various electrical signals;

Operating principles, advantages and disadvantages of analog electromechanical and electrical measuring instruments;

Rules for switching on and taking readings from instruments when measuring basic electrical quantities;

Principles of operation, preparation and rules for using radio measuring instruments: electronic voltmeters, measuring generators, electronic oscilloscopes, nonlinear distortion meters;

Symbols and markings of measurements.

1.2 Structure and content of the academic discipline

1.2.1 Scope of academic discipline and types of academic work

Type of educational work	Number of hours
Mandatory classroom teaching load (total)
including:
laboratory works
practical lessons
Independent work of the student (total)
including:
Self-study for studying sections and topics of textbooks
Preparation for laboratory work and practical classes
Preparation of messages, presentations
final examination in the form of differential credit

1.2.2. Tthematic plan and content of the academic discipline “Electrical measurements”

Name of sections and topics		Hours volume	Mastery level
Section 1. State system for ensuring unity
Topic 1.1. Main types and methods of measurements, their classification	Definition of the concept "measurement". Units of physical quantities. Classification of measurement methods and their a brief description of. Direct and indirect methods. Methods of direct assessment and comparison methods (differential, zero, substitution). The concept of measuring instruments: measures of basic electrical quantities, electrical measuring instruments, electrical measuring installations, measuring transducers, information systems. Classification and marking of electrical measuring instruments.
Independent student work - preparing a presentation on basic and additional units of measurement
Topic 1.2. Metrological indicators of measuring instruments	Errors as characteristics of measuring instruments. Types of errors and the main reasons for their occurrence. Determination of instrument error based on the accuracy class of the device. Limit, division value, sensitivity of an electrical measuring device. Typical methodology for testing electrical measuring instruments. General information processing measurement results.
Practical work 1 Determine the error of the measuring device
Independent work of the student - preparation for practical work on topic 1.2
Section 2 Instruments and methods of electrical measurements
Topic 2.1 Mechanisms and measuring circuits of electromechanical devices	Measuring mechanisms of magnetoelectric, electromagnetic, electrodynamic, ferrodynamic, electrostatic, induction systems. General principle creation of various electrical measuring mechanisms. The principle of operation of electromechanical devices. The concept of measuring circuits. Measuring circuit of electrical measuring instruments: voltmeters, ammeters, wattmeters. Symbols applied to devices.
Independent student work - preparing a presentation on symbols devices
Topic 2.2 Instruments and methods for measuring voltage	Voltage measurement methods. Device, principle of operation, specifications, varieties (classification), scope of application: electromechanical voltmeters, electronic voltmeters, digital voltmeters, compensators (hubs). Application of combined instruments for measuring voltage. Selecting a device for measuring voltage, connecting it to a circuit, measuring, processing the measurement result.
Lab 1 Voltage Measurement
Independent student work - preparation for laboratory work on topic 2.2
Topic 2.3 Instruments and methods for measuring current	Methods for measuring currents. Design, principle of operation, technical characteristics, varieties, scope of application of the main types of ammeters, current clamps. Extending measurement limits using current transformers and shunts. Application of combined instruments for current measurement. Selecting a device for measuring current, connecting it to a circuit, measuring, processing the measurement result.
Lab 2 Measuring Current
Independent student work - preparation for laboratory work on topic 1.5
Topic 2.4 Instruments and methods for measuring power and energy.	Methods for measuring power tons of electricity. Device, principle of operation, technical characteristics, types, scope of application: wattmeters and electricity meters. Selection of instruments for measuring power and electricity, connecting them to the circuit, measurement, processing of measurement results. Expansion of measurement limits.
Lab 3 Power Measurement
Lab 4 Measurement electrical energy
Independent student work - preparation for laboratory work on topic 2.4
Topic 2.5 Instruments and methods for measuring parameters of electrical circuits .	Resistance measurement. Ohmmeters. Voltmeter and ammeter method: connection circuits, their advantages and disadvantages. Errors of the method. Bridge circuits. Single bridge theory direct current. Double bridge. Measurement of parameters of capacitors and inductances. Bridge circuits. Resonant circuits. Measurements by substitution method. Measurement errors.
Lab 5 Resistance Measurement
Independent student work - preparation for laboratory work on topic 2.5
Topic 2.6 Universal and special electrical measuring instruments.	Basic parameters and types of universal and special electrical measuring instruments, brief technical characteristics. Multimeters, voltammeters, combined instruments. Diagram of the measuring circuits of the combined instrument. Digital multimeters, block diagram, switches for the type of measurements and measurement limits. Units of measurement. Multimeter input resistance. Measurement of resistances, currents, voltages, electrical capacitances, parameters of semiconductor devices.
Laboratory work 6 Measurement of electrical quantities (U, I, R) with a combined instrument
Independent student work - preparation for laboratory work on topic 2.6
Section 3 Waveform Study
Topic 3.1 Oscilloscopes	General information and classification of electron ray oscilloscopes. Device, principle of operation, purpose, technical characteristics, structural scheme cathode ray oscilloscope. Using a cathode ray oscilloscope to observe an electrical signal, to measure the amplitude, frequency and period of a periodic signal. Using a cathode ray oscilloscope to measure frequency and phase shift. Types of oscilloscopes. Block diagram of an electronic oscilloscope. Preparation, calibration and measurement various signals. Features of preparation, calibration and measurements with two-beam, oscilloscopes-multimeters and oscilloscopes with information storage. Features of measuring non-electrical quantities with electronic oscilloscopes Analog oscilloscopes, digital storage oscilloscopes, digital phosphor oscilloscopes, digital stroboscopic oscilloscopes, virtual oscilloscopes, portable oscilloscopes
Practical work 2 Study of signal shapes on a cathode ray oscilloscope
Independent student work - preparation for laboratory work on topic 2.4
Topic 3.2 Instruments and methods for measuring frequency and time interval	Methods for measuring frequency and time interval. Design, principle of operation, technical characteristics, types, scope of application of frequency meters. Measuring time intervals. Measuring generators. Block diagram. Generators R-C, L-C, on beats, noise, standard signals, impulse. Characteristics of signals. Rules for setting up and connecting. Matching devices. Safety regulations .
Lab 7 Frequency Measurement alternating current
Independent student work - preparation for laboratory work on topic 3.2
Topic 3.3 Instruments and methods for measuring phase shift.	Methods for measuring phase shift. Design, principle of operation, technical characteristics, types, scope of application of phase meters.
Lab 8 Measuring phase angle
Independent student work - preparing a presentation message about the types of phase meters

1.3 Conditions for the implementation of the academic discipline

Goal of the work: study methods for measuring electrical quantities, the operating principle of devices of magnetoelectric, electromagnetic, electrodynamic and induction systems, calculate the measurement error.

Work progress:

Objects electrical measurements are all electrical and magnetic quantities: current, voltage, power, energy, magnetic flux, etc.

Electrical measuring devices are also widely used to measure non-electrical quantities (temperature, pressure, etc.), which for this purpose are converted into electrical quantities proportional to them. Such measurement methods are known collectively as electrical measurements of non-electrical quantities. The use of electrical measurement methods makes it possible to relatively easily transmit instrument readings over long distances (telemetering), control machines and devices (automatic control), and perform automatic mathematical operations over measured quantities, record (for example, on tape) the progress of controlled processes, etc.

Based on the type of reading device, analogue and digital devices are distinguished. In analog instruments, the quantity being measured or proportional to it directly affects the position of the moving part on which the reading device is located. In digital instruments there is no moving part, and the quantity being measured or proportional to it is converted into a numerical equivalent that is recorded digital indicator. Microprocessors can significantly improve the performance and accuracy of measuring instruments, giving them additional functions processing measurement results. For research complex objects automatic measuring systems are used, which are a set of sensors, measuring and recording devices, devices for their coupling (interface) and control.

The measurement of any physical quantity consists of comparing it through a physical experiment with the value of the corresponding physical quantity, called a measure, taken as a unit. Such a comparison is possible using either a comparison device or a direct reading device, also called an indicating device. In the latter case, the measured value is determined by the scale of the device, for the calibration of which a measure is required. Depending on how the measurement results are obtained, measurements are distinguished between direct, indirect and cumulative.

If the result of a measurement directly gives the desired value of the quantity under study, then such a measurement belongs to the group straight, for example, measuring current with an ammeter.

If the measured quantity has to be determined on the basis of direct measurements of other physical quantities with which the measured quantity is related by a certain relationship, then the measurement refers to indirect, such as measuring element resistance electrical circuit when measuring voltage with a voltmeter and current with an ammeter. It should be borne in mind that with indirect measurement, a significant decrease in accuracy is possible compared to the accuracy with direct measurement due to the addition of errors in direct measurements of quantities included in the calculation equations.

Depending on the method of using instruments and measures, it is customary to distinguish the following main measurement methods: direct, zero and differential.

When using direct measurement method(or direct reading) the measured quantity is determined by directly reading the reading of a measuring device or direct comparison with a measure of a given physical quantity (measuring current with an ammeter, measuring length with a meter). In this case, the accuracy of the measurement is determined by the accuracy of the indicating device.

When measuring zero method the value of a standard (known) quantity (or the effect of its action) is adjusted until it is equal to the value of the measured quantity (or the effect of its action), which is recorded by the measuring device. The device must be high sensitivity, it is called zero device, or zero – indicator. The measurement accuracy of the zero method is very high and mainly depends on the accuracy of the reference measures and the sensitivity of the zero instruments. The most important among zero methods of electrical measurements are bridge and compensation.

Even greater accuracy can be achieved with differential methods measurements. In these cases, the measured quantity is balanced by a known quantity not to complete equilibrium, but by direct reading, the difference between the measured and known quantities is measured. Differential methods are used to compare two quantities whose values ​​differ little.

The measurement accuracy is characterized by its possible errors. These errors for each specific measurement should not exceed a certain value. Depending on the method of numerical expression, errors are distinguished between absolute and relative, and in relation to indicating instruments - also reduced.

Absolute error ∆A is the difference between the measured And from and the actual values ​​of the measured quantity:

∆A =A from - A(1)

For example, an ammeter shows A from =9 A, and the actual current value A = 8.9 A, hence, ∆A = 0.1 A.

To determine the actual value of a quantity, you need to add a correction to the measured value - the absolute error taken with the opposite sign.

The measurement accuracy is usually assessed not as absolute, but relative error– expressed as a percentage, the ratio of the absolute error to the actual value of the measured value:

And since the difference between A And And from is usually relatively small, then in almost most cases it can be assumed that

. (3)

For the given example of current measurement, the relative error

.

To assess the accuracy of the indicating measuring instruments themselves, they are reduced error. This is the name given to the ratio of the absolute error of indication expressed as a percentage. ∆A To A nom.– nominal value corresponding to the highest reading of the device:

, (4)

If in the considered example the measurement limit of the ammeter A nom = 10 A, then its reduced error

Device errors are caused by shortcomings of the device itself and external influences. The given error, depending only on the device itself, is called main error.

The permissible basic error of an electrical measuring device determines its accuracy class. The designation of the accuracy class is the permissible basic error of instruments belonging to this class: 0.05; 0.1; 0.2; 0.5; 1; 1.5; 2.5; 4. Belonging of a device to a certain class indicates that the basic error of the device at all scale divisions does not exceed the value determined by the accuracy class of this device (for example, for a device of class 1 the permissible basic error is 1%). Deviation of external conditions from normal causes additional errors.

Depending on the sensitivity to external magnetic or electric fields, electrical measuring instruments are divided into two categories: 1 - less sensitive devices and 2 - more sensitive devices.

Any direct reading device consists of two main parts: a measuring mechanism and a measuring circuit (measuring circuit).

Purpose measuring mechanism– conversion of electrical energy supplied to it into mechanical energy of movement of the moving part and the indicator associated with it. Measuring chain converts the measured electrical quantity (voltage, current, power, etc.) into a quantity proportional to it, directly affecting the measuring mechanism. For example, in a voltmeter, the measuring circuit consists of a measuring mechanism coil and an additional resistor. If the resistance of the measuring circuit is constant, the current in the measuring mechanism of the voltmeter is proportional to the measured voltage.

The same measuring mechanism, in connection with different measuring circuits, can be used to measure different quantities.

Depending on the principle of operation of the measuring mechanism, several systems of indicating devices are distinguished (magnetoelectric, electromagnetic, electrodynamic, induction, etc.).

In measuring mechanisms magnetoelectric system the torque is created by the interaction of the measured direct current in the mechanism coil with the field of a permanent magnet. There are two main types of magnetoelectric system devices: devices with a moving coil (moving frame) and devices with a moving magnet, and the former are used much more often than the latter.

In a magnetoelectric mechanism with a moving coil (Fig. 1), the latter is mounted on supports and can rotate in the air gap of the magnetic circuit of permanent magnet 1.

The magnetic circuit of the measuring mechanism is formed by a magnetic circuit 2, pole pieces 3 and a cylindrical core 4, which are made of soft magnetic material.

The angle between the directions of the magnetic induction vector IN in the air gap and current I in the active part of the conductors with a length l moving coil is 90 0. Consequently, an electromagnetic force acts on each of the conductors:

and on the moving part of the mechanism - torque:

where d is the diameter of the coil frame with the number of turns ω and cross-sectional area S = l d; k vr = ω S d – proportionality coefficient.

Since the counteracting moment created by coil springs is directly proportional to the angle of twist, i.e. M pr = k pr α , then the angle of rotation of the coil with equal moments M vr = M pr is directly proportional to the measured current:

,

where C pr is the device constant (“division price”).

A permanent magnet creates a strong magnetic field in the air gap of the magnetic circuit of the device (0.2-0.3 T), and even at low values ​​of the measured currents, sufficient torque can be obtained. Therefore, magnetoelectric devices are very sensitive, external magnetic fields affect their readings, and their own energy consumption is relatively low.

To expand the measurement limits, devices of the magnetoelectric system, as well as devices of other systems, are equipped with a set of resistors for dividers of the measured quantities. A resistor connected in series with the coil of the measuring mechanism is called additional resistor; a resistor that is connected in parallel with the coil of the measuring mechanism or with a branch containing a coil and an additional resistor is called shunt.

When the direction of the current changes, the direction of the torque also changes. With alternating current, rapidly alternating torques in the opposite direction act on the moving part of the device. Their resulting action will not change the position of the moving part of the device. To measure alternating current, the magnetoelectric measuring mechanism must be connected to the transducer. The converter can be, for example, a full-wave rectifier.

In measuring mechanisms electromagnetic system the torque is caused by the action of the magnetic field of the measured current in the stationary coil of the device on the movable ferromagnetic armature. Mechanical forces in such a device tend to move the armature so that the energy of the device’s magnetic field becomes as large as possible.

The magnetic field of the device is excited by the measured current itself and is relatively weak, since most of the path of the magnetic flux occurs in the air. For this reason, the measuring mechanism of the electromagnetic system has low sensitivity. Due to the weakness of its own magnetic field, the device must be protected from external magnetic influences. For this purpose, ferromagnetic screens are used or the measuring mechanisms are made astatic.

The general principle of the astatic device of the measuring system is as follows. The number of coils in the mechanism doubles, and both coils participate equally in the generation of torque, but their own magnetic fields have opposite directions. Any external uniform magnetic field, strengthening the magnetic field of one coil, also weakens the magnetic field of the second coil. As a result, the external magnetic field does not change the overall torque of the measuring mechanism.

The accuracy class of electromagnetic instruments is usually no higher than 1.5, mainly due to the influence of hysteresis (residual magnetization), which is especially noticeable when measuring direct current, and energy losses due to magnetization reversal when measuring alternating current.

The electromagnetic measuring mechanism has a number of valuable properties. A fixed coil with current can easily be made with a sufficient reserve of wire cross-section in case of overload. The devices of this system allow large overloads, are cheap and simple in design. Electromagnetic instruments mainly measure variable voltage and currents (low frequencies). In industrial installations of low frequency alternating current, most ammeters and voltmeters are devices of the electromagnetic system.

IN electrodynamic measuring mechanisms To create torque, the interaction of two coils with currents is used.

The measuring mechanism of this system consists mainly of a fixed and a moving coil. The counteracting moment is created by special springs, which at the same time serve to supply current to the moving coil. The latter, under the influence of electromagnetic forces, tends to take a position in which the direction of its magnetic field coincides with the direction of the field of the stationary coil (the maximum energy of the total magnetic field).

Since the device has two coils, the scope of application of this mechanism can be significantly expanded. Depending on the purpose of the device, the nature of its scale also changes.

In a voltmeter, both coils with large numbers of turns are usually connected in series with each other and in series with an additional resistor.

In electrodynamic ammeters for currents up to 0.5 A, the moving and stationary coils are connected in series. At a larger value of the measured current I, the moving and fixed coils are connected in parallel.

Electrodynamic devices are suitable for measurements in both direct and alternating current circuits, and in both cases the scale of the devices is the same.

In an electrodynamic device, the measured currents excite a relatively weak magnetic field in the air. Therefore, to obtain sufficient torque, measuring mechanism coils with large numbers of turns are needed and the device’s own energy consumption is relatively high. Due to the weak magnetic field, the device is sensitive to external magnetic influences; To protect against these influences, the devices have screens. Since cooling conditions are poor (heat transfer through a layer of air), electrodynamic mechanisms do not allow any significant overload (especially ammeters). Finally, the devices of this system are expensive. However, due to the absence of ferromagnetic cores in the magnetic field - elements with nonlinear properties - the accuracy of the electrodynamic device can be high - class 0.2 and even 0.1.

Induction measuring system based on the use of a rotating magnetic field. If the sinusoidal currents in two coils, oriented in a certain way in space, are out of phase, then in part of space the resulting magnetic field of these two coils will rotate around a certain axis. If on this axis there is a body made of material with small resistivity, then eddy currents will arise in it. The interaction of eddy currents with a rotating magnetic field creates a torque, under the influence of which the body will begin to move.

In an induction measuring mechanism, torque is created by the action of the resulting magnetic field of two alternating current electromagnets on a moving part - an aluminum disk, in which this field induces eddy currents. Electromagnets are excited by measured alternating currents. Therefore, the value of the torque depends on the current values ​​in both electromagnets and the phase shift angle between them. This valuable property of the induction measuring mechanism forms the basis for the construction of instruments for measuring power and energy in alternating current circuits.

Control questions and tasks

List the areas of application of electrical measurement methods.

What is the difference between analog and digital instruments?

What is meant by measuring a physical quantity?

Which measurements are considered direct and which are indirect?

Explain the essence of direct, zero and differential measurement methods.

Write down the definitions and formulas for absolute and relative errors.

What does the accuracy class of a device mean?

What are the main parts of a direct reading device?

Explain the principles of operation of devices of the magnetoelectric, electromagnetic, electrodynamic and induction systems.

Determine the absolute and reduced error of a voltmeter designed for 250 V, if the actual voltage value is 200 V, and the voltmeter shows 206.25 V.

Practical work No. 10

Measurement is an information process of obtaining, experimentally, a numerical relationship between a given physical quantity and a standard.

Measurement result– a named number found by measuring a physical quantity. The actual value of the measured quantity can be taken as the measurement result. One of the main tasks of measurement is assessing the degree of approximation or difference between the true and actual values ​​of the measured physical quantity - assessing the measurement error .

Measurement errors is the deviation of the measurement result from the true value of the measured value. Measurement error is a direct characteristic of measurement accuracy.

Measurement accuracy– the degree of closeness of the measurement result to the true value of the measured physical value. quantities. Measurement reduces the initial uncertainty in the value of a physical quantity to the level of inevitable residual uncertainty determined by the measurement error. The measurement error value depends on the degree of perfection technical means measurements (accuracy class), method of their use and experimental conditions .

The accuracy class is the given relative error expressed as a percentage:

,

where is a normalized number. Usually the limit value (scale) of the instrument reading is taken as the limit value.

Example: Instrument scale 150V, instrument accuracy class 0.5. The measurement error will be:

.

Measuring principle is a physical phenomenon or set of physical phenomena, which form the basis of the measurement.

Example : Temperature measurement using a thermal effect (thermocouple). Current measurement - interaction of a current frame with a magnetic field .

Measuring experiment is a scientifically based experience for obtaining quantitative information with the required accuracy or possible accuracy in determining the measurement result. Carrying out a measurement experiment presupposes the availability of technical equipment. devices that can provide specified accuracy getting the result. The technical devices involved in the experiment are standardized in advance in terms of accuracy and are classified as measuring instruments.

Measuring instrument- This technical device, used in a measurement experiment and having normalized accuracy characteristics.

Measuring information– this is quantitative information about the properties of a material object, phenomenon or process, obtained using measuring instruments as a result of their interaction with the object. The unit of measurement is bytes.

Quantity of measurement information is a numerical measure of reducing the uncertainty in the quantitative assessment of the properties of an object. The interaction of the object of study and measuring instruments during the experiment presupposes the presence of signals that are carriers of information. Important information carriers are electricity, voltage, current pulses and other parameters.

Measuring signal– a signal functionally associated with a measured physical quantity with a given accuracy.

Method of measurement is a set of techniques for using the principles and means of measurement.

For example: Measuring the capacitance of a capacitor by measuring the voltage drop across the capacitor with a digital voltmeter.

Unity of measurements– a state of measurements in which their results are expressed in specified units, and measurement errors are known with a given probability. The uniformity of measurements makes it possible to compare the results of different experiments carried out in different conditions, made in different places using different methods and measuring instruments. This is achieved by accurately reproducing and storing the establishment of units of physical quantities and transferring their sizes to the measuring instruments used. The questions listed above constitute the subject of metrology.

Measurement of electrical quantities

In alternating current circuits, electromechanical devices mainly measure not the amplitude, but the effective value of a sinusoidal quantity. Effective value less amplitude value 1.41 times. .

Current measurement– an ammeter is used to measure current. The ammeter is connected in series with the object being measured. The internal resistance of an ideal ammeter is zero.

Rice. – Electrical diagram turning on the ammeter

Voltage measurement– a voltmeter is used to measure voltage. The voltmeter is connected to the circuit parallel to the object being measured. The internal resistance of an ideal voltmeter is zero.

Rice. – Electrical circuit for switching on a voltmeter

Active power measurement

A wattmeter is used to measure active power. A wattmeter has four ends: two ends are connected in parallel to the object being measured - like a voltmeter, and two ends are connected in series with the object being measured - like an ammeter.

Rice. – Electrical circuit for switching on the wattmeter

Resistance measurement.

An ohmmeter is used to measure resistance. The amount of resistance can be measured indirectly using Ohm's law by measuring the current flowing through the resistance and measuring the drop or by comparison with a standard.

Possible Internet testing questions on the topic 7(electrical measurements):

1. The internal resistance of an ideal voltmeter is:

(a) zero;

(b) infinity;

2. The internal resistance of an ideal ammeter is:

(a) zero;

(b) infinity;

(V) internal resistance source;

(d) output resistance of the measurement circuit.

3. Accuracy class of the measuring device:

(a) relative error;

(b) reduced relative error expressed as a percentage;

(c) scaled error;

(d) absolute error expressed as a percentage.

4. The wattmeter measures:

(a) Reactive power

(b) Active power

(c) Total power S

(d) power factor

Related information.

Tutorial intended for students educational institutions secondary vocational education, students in the specialty “Installation, adjustment and operation of electrical equipment of enterprises and civil buildings.” It may be useful for students of related specialties whose education program includes measurement issues in energy systems with voltages up to 1000 V and in low-frequency electrical circuits.

Definition and classification of measurements, methods and measuring instruments. Units of physical quantities.
The Federal Law “On Ensuring the Uniformity of Measurements” dated April 27, 1993 regulates relations related to ensuring the uniformity of measurements in Russian Federation, in accordance with the Constitution of the Russian Federation.
The main articles of the Law establish:
basic concepts used in the Law;
organizational structure government controlled ensuring uniformity of measurements;
regulations to ensure uniformity of measurements;
units of quantities and state standards of units of quantities;
measurement tools and techniques.
The law defines the State Metrological Service and other services to ensure the uniformity of measurements, metrological services of state governing bodies and legal entities, as well as types and areas of distribution of state metrological control and supervision. Separate articles of the Law contain provisions for calibration and certification of measuring instruments and establish types of liability for violation of the Law. The emergence of market relations left its mark on the article of the Law, which defines the fundamentals of the activities of metrological services of state governing bodies and legal entities. The activities of structural units of metrological services at enterprises are stimulated by purely economic methods.

In areas that are not controlled government agencies, a Russian calibration system is being created, also aimed at ensuring the uniformity of measurements. Gosstandart of the Russian Federation appointed the central body Russian system calibration Department of technical policy in the field of metrology.

Table of contents
Introduction
Chapter 1. BASIC INFORMATION ABOUT METROLOGY. MEASUREMENT METHODS AND ERRORS
1.1.Definition and classification of measurements, methods and measuring instruments. Units of physical quantities
1.2.Measurement errors
1.3.Systematic errors
1.4.Random errors
1.5.Rules and forms for presenting measurement results
1.6.Characteristics of electrical measuring instruments
Chapter 2. UNITY OF MEASUREMENTS. MEASURES OF BASIC ELECTRICAL QUANTITIES
2.1.Ensuring uniformity of measurements
2.2.Verification of measuring instruments
2.3.Calibration of measuring instruments
2.4. Verification (calibration) methods and verification schemes
2.5. Certification of measuring instruments
2.6.Classification of measures
2.7.Measures of units of electrical quantities
2.8. Standards of units of electrical quantities
Chapter 3. GENERAL INFORMATION ABOUT ANALOG ELECTRICAL DEVICES
3.1.General questions
3.2.Technical requirements
3.3.Reading devices
3.4. Support devices and devices for creating a counteracting moment
3.5.Devices for creating a calming moment
Chapter 4. CURRENT AND VOLTAGE CONVERTERS
4.1.Shunts and additional resistors
4.2.Measuring transformers. Galvanic isolation
4.3.Measuring current transformers
4.4.Measuring voltage transformers
4.5.Hall sensors
Chapter 5. MEASURING MECHANISMS OF DEVICES AND THEIR APPLICATION
5.1.General information
5.2.Magnetoelectric mechanisms
5.3.Ammeters and voltmeters of the magnetoelectric system
5.4.Electrodynamic and ferrodynamic mechanisms
5.5.Ammeters and voltmeters of electrodynamic and ferrodynamic systems
5.6.Wattmeters of electrodynamic and ferrodynamic systems
5.7.Mechanisms of the electromagnetic system
5.8.Electrostatic mechanisms and their application
Chapter 6. ELECTRICAL MEASURING CIRCUITS
6.1. General information
6.2.Basic equations and properties of measuring transducers
6.3. Measuring circuit as a converter
6.4.Error correction methods
6.5.Bridge circuits
6.6.Compensation circuits
Chapter 7. ELECTRONIC MEASURING INSTRUMENTS
7.1.Electronic analog voltmeters
7.2.Chode ray oscilloscopes
7.3.Digital oscilloscopes
Chapter 8. DIGITAL MEASURING INSTRUMENTS AND ANALOG-DIGITAL CONVERTERS
8.1.Basic concepts
8.2.Analog-to-digital converters and digital voltmeters
Chapter 9. MEASUREMENT OF CURRENTS AND VOLTAGES
9.1.Methods for measuring direct currents and voltages
9.2.Measurement methods alternating currents and power frequency voltages
Chapter 10. MEASUREMENT OF PARAMETERS OF ELECTRICAL CIRCUITS AND COMPONENTS
Chapter 11. POWER MEASUREMENT
11.1. General information
11.2.Power measurement in DC circuits
11.3.Measurement of active power in alternating current circuits
Chapter 12. ENERGY MEASUREMENT
12.1.Single-element induction meter
12.2. Two- and three-element induction meters
12.3. Schemes for connecting meters
12.4.Electronic meters
Chapter 13. MEASUREMENT OF PHASE SHIFT, FREQUENCY AND ELECTRIC ENERGY QUALITY INDICATORS. ELECTROMAGNETIC COMPATIBILITY
13.1.Phase shift measurement
13.2 Frequency measurement
13.3.Electromagnetic compatibility. Measuring electrical energy quality indicators
Chapter 14. MEASURING AND INFORMATION SYSTEMS
14.1.General information
14.2.Basic structures of the IIS
14.3. Complex CAMAC (SAMAS)
14.4.Device interface IEC 625.1
Literature.

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