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Voltage measuring device. How to measure voltage with a multimeter. Current voltage In what units is electric current voltage measured?

In practice, voltage measurements have to be performed quite often. Voltage is measured in radio engineering, electrical devices and circuits, etc. The type of alternating current can be pulsed or sinusoidal. Voltage sources are either current generators.

Types of voltage measurements

Pulse current voltage has amplitude and average voltage parameters. Sources of such voltage can be pulse generators. Voltage is measured in volts and is designated “V” or “V”. If the voltage is alternating, then the symbol “ ~ ", for constant voltage the symbol "-" is indicated. The alternating voltage in the home household network is marked ~220 V.

These are instruments designed to measure and control the characteristics of electrical signals. Oscilloscopes work on the principle of deflecting an electron beam, which produces an image of the values of variable quantities on the display.

AC voltage measurement

According to regulatory documents, the voltage in a household network must be equal to 220 volts with a deviation accuracy of 10%, that is, the voltage can vary in the range of 198-242 volts. If the lighting in your home has become dimmer, lamps have begun to fail frequently, or household devices have become unstable, then to identify and eliminate these problems, you first need to measure the voltage in the network.

Before measurement, you should prepare the existing measuring device for use:

Check the integrity of the insulation of control wires with probes and tips.
Set the switch to AC voltage, with an upper limit of 250 volts or higher.
Insert the test leads into the sockets of the measuring device, for example. To avoid mistakes, it is better to look at the designations of the sockets on the case.
Turn on the device.

The measurement limit of 700 volts is selected on the multimeter. Some devices require that several different switches be set to the desired position in order to measure voltage: the type of current, the type of measurement, and also insert the wire tips into certain sockets. The end of the black tip in the multimeter is inserted into the COM socket (common socket), the red tip is inserted into the socket marked “V”. This socket is common for measuring any kind of voltage. The socket marked “ma” is used for measuring small currents. The socket marked “10 A” is used to measure a significant amount of current, which can reach 10 amperes.

If you measure the voltage with the wire inserted into the “10 A” socket, the device will fail or the fuse will blow. Therefore, you should be careful when performing measuring work. Most often, errors occur in cases where the resistance was first measured, and then, forgetting to switch to another mode, they begin to measure the voltage. In this case, a resistor responsible for measuring resistance burns out inside the device.

After preparing the device, you can begin measurements. If nothing appears on the indicator when you turn on the multimeter, this means that the battery located inside the device has expired and requires replacement. Most often, multimeters contain “Krona”, which produces a voltage of 9 volts. Its service life is about a year, depending on the manufacturer. If the multimeter has not been used for a long time, the crown may still be faulty. If the battery is good, the multimeter should show one.

The wire probes must be inserted into the socket or touched with bare wires.

The multimeter display will immediately display the network voltage in digital form. On a dial gauge, the needle will deviate by a certain angle. The pointer tester has several graduated scales. If you look at them carefully, everything becomes clear. Each scale is designed for a specific measurement: current, voltage or resistance.

The measurement limit on the device was set to 300 volts, so you need to count on the second scale, which has a limit of 3, and the readings of the device must be multiplied by 100. The scale has a division value equal to 0.1 volts, so we get the result shown in the figure, about 235 volts. This result is within acceptable limits. If the meter readings constantly change during measurement, there may be poor contact in the electrical wiring connections, which can lead to arcing and network faults.

DC voltage measurement

Sources of constant voltage are batteries, low-voltage or batteries whose voltage does not exceed 24 volts. Therefore, touching the battery poles is not dangerous, and there is no need for special safety measures.

To assess the performance of a battery or other source, it is necessary to measure the voltage at its poles. For AA batteries, the power poles are located at the ends of the case. The positive pole is marked “+”.

Direct current is measured in the same way as alternating current. The only difference is in setting the device to the appropriate mode and observing the polarity of the terminals.

The battery voltage is usually marked on the case. But the measurement result does not yet indicate the health of the battery, since the electromotive force of the battery is measured. The duration of operation of the device in which the battery will be installed depends on its capacity.

To accurately assess the performance of the battery, it is necessary to measure the voltage with a connected load. For a AA battery, a regular 1.5 volt flashlight light bulb is suitable as a load. If the voltage decreases slightly when the light is on, that is, by no more than 15%, therefore, the battery is suitable for operation. If the voltage drops significantly more, then such a battery can only serve in a wall clock, which consumes very little energy.

We take electricity for granted and hardly anyone thinks about what electrical voltage is and what its physical essence is when they turn on the light, computer or washing machine. In fact, it deserves much more attention, and not only because it can be deadly, but also because Humanity, having mastered this type of energy, has made a qualitative leap in civilization.

Let's remember one of the most interesting moments in a school physics lesson, when the teacher rotated the disk of an electric machine, and a spark jumped between the metal balls. This is the visible reflection of a natural phenomenon called electric current. It arises due to the fact that there are more negatively charged ions on one ball and fewer on the other, which is why a potential difference arises, that is, a fact that violates the basic law of Nature - conservation of energy.

Negatively charged particles tend to move to where there are fewer of them, thereby nullifying the difference. Of course, electrons do not travel all the way between the charged balls, called poles. Their range is limited by a crystal lattice, the nodes of which they cannot leave. But they are capable of hitting neighboring particles and transmitting momentum further along the chain, creating a domino effect. Each such collision generates a burst of energy, due to which the system passes from a resting state to an excited one, which is usually called electrical voltage.

The force that moves charged particles

In order to put electric voltage and current at his service, man had to find a force that could restore the potential difference between the poles, generating a continuous collision of particles of the crystal lattice. There were three of them:

Electromagnetic induction is the generation of current as a result of the interdependent movement of metals in a magnetic field. Used in direct and alternating current generators.
Electrochemical interaction generated by the potential difference between the crystal lattices of substances. Used in batteries, DC batteries.
A thermochemical reaction that increases the activity of electrons as a result of heating.

The force that generates the movement of charged particles is called “electromotive” (abbreviation EMF) and is indicated on diagrams by the letter “E”, usually accompanying the mnemonic symbols of the connectors to which the power source is connected.

Volts and Amps

EMF and voltage are measured in volts - a conventional unit named after the Italian Alessandro Volta, the officially recognized inventor of the galvanic battery - a direct current source. This is the amount of work that is done when moving a unit of charge (coulomb), if 1 joule of conventional energy was spent.

However, there is a second unit of measurement of electric current - the ampere, named after the French physicist Andre-Marie Ampere. Traditionally, it is called current strength, although it is more correct to use the term “magnetomotive force”, which most fully reflects the dual physical essence of a charged particle.

The magnetic and electric fields of the electron tend to mutually compensate, and their dependence is determined by Ohm's law, described by the formula I = U / R. If the resistance of the medium drops sharply (for example, during a short circuit), then the current increases exponentially. This causes a response voltage drop, causing the system to return to equilibrium. A similar effect can be noticed during operation of a welding transformer, when when an arc occurs, the incandescent lamps almost go out.

There is another effect: with a high resistance of the medium, a charge of the same sign accumulates on any surface until the voltage reaches a critical level, after which a breakdown (current occurs) occurs in the direction of the surface with the greatest potential difference. Static voltage is extremely dangerous because at the moment of discharge it can generate currents of hundreds of amperes. Therefore, metal structures that are exposed to a magnetic field for a long time must be grounded.

Constant or variable?

Voltage is the static component of electricity, and current is dynamic, because its direction changes along with the polarity at the ends of the conductor. And this property turned out to be very useful for the spread of electricity throughout the World. The fact is that any current is damped due to the internal resistance of the medium, according to the same law of conservation of energy. But it turned out that it is very difficult to amplify a flow of electrons moving in one direction, but one that changes direction cyclically is simple; for this, a transformer with two windings on one core is used.

To obtain alternating current, it is necessary to turn inside out the principle discovered by Faraday, who, in his prototype of an electric generator, rotated a copper disk in the field of a permanent magnet. Nikola Tesla did the opposite - he placed a rotating electromagnet inside a stationary winding, obtaining an unexpected effect: at the moment the poles pass through the neutral of the magnetic field, the voltage amplitude drops to zero, and then increases again, but with a different sign. During one revolution, the direction of movement of electrons in the conductor changes twice, constituting the working phase. Therefore, alternating current is also called phase current. And the voltage generating it is sinusoidal.

Nikola Tesla created a generator with two windings located at an angle of 90 0 to each other, and the Russian engineer M.O. Dolivo-Dobrovolsky improved it by placing three on the stator, which increased the stability of the electric machine. As a result, industrial alternating current became three-phase.

Why 220 volts 50 Hz?

In our country, a household single-phase network has ratings of 220 volts and 50 hertz. The reason for the appearance of these particular numbers is very interesting.

The palm in the domestic development of electricity belongs to Thomas Edison. He used exclusively direct current, since Nikola Tesla's brilliant invention of alternating current had not yet happened.

The first electrical device was an incandescent lamp with a carbon filament. It was experimentally found that it works best at a voltage of 45 volts and a ballast resistance included in the circuit, which ensures the dispersion of another twenty. An acceptable operating time was ensured by switching on two lamps in series. In total, in the household network, according to Edison, there should have been 110 volts.

However, the transmission of direct current from power plants to consumers was accompanied by great difficulties: after one or two miles it died out completely. According to the Joule-Lenz Law, the amount of heat dissipated by a conductor during the passage of current is calculated by the following formula: Q = R. I 2. To reduce losses by four times, the voltage was increased to 220 volts, and the power line was built from three conductors - with two “pluses” and one “minus”. The consumer received the same 110 volts.

The confrontation between Nikola Tesla and Thomas Edison, called the “War of Currents,” was decided in favor of alternating current, since it could be transmitted over long distances with minimal losses. Nevertheless, the voltage between the power conductors remains 220, and the linear voltage supplied to the consumer is 127 volts, since due to a phase shift of 120 degrees, the voltage amplitudes do not add up arithmetically, but are multiplied by 1.73 - the square root of three.

In the USSR, the network rating of 127 volts in one phase was used until the early 60s. During the improvement of electrical lines, carried out in order to increase the transmitted power, the designers followed the same path as Edison - they increased the voltage.

The reference point was 220 volts, which were measured between phases. It has become commonplace. And the industrial phase-to-phase voltage of 380 volts was obtained by multiplying 220 by 1.73. A frequency of 50 Hz is 3 thousand vibrations per minute, that is, the optimal number of revolutions of the crankshaft of a diesel engine or other internal combustion engine that drives an alternating current machine.

Now you know what voltage and electric current are, in what units they are measured and how they depend on each other, and also why there is 220 volts in your outlet. The facts presented are not of an academic nature and do not claim to be the ultimate truth. You can learn more about the nature of this phenomenon in textbooks on electrical engineering.

Let's consider the basic electrical quantities that we study first at school, then in secondary and higher educational institutions. For convenience, we will summarize all the data in a small table. Definitions of individual quantities will be given after the table in case of any misunderstandings.

Magnitude	SI unit	Name of electrical quantity
q	Kl - pendant	charge
R	Om - om	resistance
U	V – volt	voltage
I	A – ampere	Current strength (electric current)
C	F – farad	Capacity
L	Gn - Henry	Inductance
sigma	CM - Siemens	Electrical conductivity
e0	8.85418781762039*10 -12 F/m	Electrical constant
φ	V – volt	Electric field point potential
P	W – watt	Active power
Q	VAR – volt-ampere-reactive	Reactive power
S	Va – volt-ampere	Full power
f	Hz - hertz	Frequency

There are decimal prefixes that are used in the name of the quantity and serve to simplify the description. The most common of them are: mega, miles, kilo, nano, pico. The table shows other prefixes, except those mentioned.

Decimal multiplier	Pronunciation	Designation (Russian/international)
10 -30	cuecto	q
10 -27	ronto	r
10 -24	iocto	and/y
10 -21	zepto	s/z
10 -18	atto	a
10 -15	femto	f/f
10 -12	pico	p/p
10 -9	nano	n/n
10 -6	micro	μ/μ
10 -3	Milli	m/m
10 -2	centi	c
10 -1	deci	d/d
10 1	soundboard	yes/da
10 2	hecto	g/h
10 3	kilo	k/k
10 6	mega	M
10 9	giga	G/G
10 12	tera	T
10 15	peta	P/P
10 18	exa	E/E
10 21	zeta	Z/Z
10 24	yotta	Y/Y
10 27	Ronna	R
10 30	quecca	Q

Current strength is 1A- this is a value equal to the ratio of a charge of 1 C passing through a surface (conductor) in 1 s of time to the time of passage of the charge through the surface. For current to flow, the circuit must be closed.

Current strength is measured in amperes. 1A=1Kl/1c

In practice there are

1uA = 0.000001A

Electrical voltage– potential difference between two points of the electric field. The magnitude of electrical potential is measured in volts, therefore voltage is measured in volts (V).

1 Volt is the voltage that is necessary to release 1 Watt of energy in a conductor when a current of 1 Ampere flows through it.

In practice there are

Electrical resistance– the characteristic of a conductor to prevent electric current from flowing through it. It is defined as the ratio of the voltage at the ends of the conductor to the current in it. Measured in ohms (ohms). Within certain limits the value is constant.

1 Ohm is the resistance of a conductor when a direct current of 1A flows through it and a voltage of 1V arises at the ends.

From the school physics course we all remember the formula for a homogeneous conductor of constant cross-section:

R=ρlS – the resistance of such a conductor depends on the cross-section S and length l

where ρ is the resistivity of the conductor material, tabular value.

Between the three quantities described above, Ohm's law exists for a DC circuit.

The current in the circuit is directly proportional to the voltage in the circuit and inversely proportional to the resistance of the circuit - .

Electrical capacity is the ability of a conductor to accumulate electrical charge.

Capacitance is measured in farads (1F).

1F is the capacitance of a capacitor between the plates of which a voltage of 1V occurs when charged at 1C.

In practice there are

1pF = 0.000000000001F

1nF = 0.000000001F

Inductance is a quantity that characterizes the ability of a circuit through which an electric current flows to create and accumulate a magnetic field.

Inductance is measured in henries.

1Gn = (V*s)/A

1H is a value equal to the self-inductive emf that occurs when the current in the circuit changes by 1A within 1 second.

In practice there are

1mH = 0.001H

Electrical conductivity– a value indicating the ability of a body to conduct electric current. Reciprocal of resistance.

Electrical conductivity is measured in siemens.

What is a volt equal to?

This parameter can be either constant or variable. It is alternating current that “flows” into apartments, buildings and structures, houses and organizations. Electrical voltage represents amplitude waves, indicated on graphs as a sine wave.

Alternating current is indicated in diagrams by the symbol “~”. And if we talk about what one volt is equal to, then we can say that this is an electrical action in a circuit where, when a charge equal to one coulomb (C) flows, work equal to one joule (J) is performed.

The standard formula by which it can be calculated is:

U = A:q, where U is exactly the desired value; “A” is the work that the electric field (in J) does to transfer charge, and “q” is precisely the charge itself, in coulombs.

If we talk about constant values, then they practically do not differ from variables (with the exception of the construction graph) and are produced from them, using a rectifying diode bridge. Diodes, without passing current to one side, seem to divide the sine wave, removing half-waves from it. As a result, instead of phase and zero, we get plus and minus, but the calculation remains in the same volts (V or V).

Voltage measurement

Previously, only an analog voltmeter was used to measure this parameter. Now on the shelves of electrical engineering stores there is a very wide range of similar devices already in digital design, as well as multimeters, both analog and digital, with the help of which the so-called voltage is measured. Such a device can measure not only the magnitude, but also the current strength, the resistance of the circuit, and it is even possible to check the capacitance of the capacitor or measure the temperature.

Of course, analog voltmeters and multimeters do not provide the same accuracy as digital ones, the display of which shows the voltage unit down to hundredths or thousandths.

When measuring this parameter, the voltmeter is connected to the circuit in parallel, i.e. if it is necessary to measure the value between phase and zero, the probes are applied one to the first wire, and the other to the second, in contrast to measuring current, where the device is connected in series to the circuit.

In circuit diagrams, a voltmeter is indicated by the letter V surrounded by a circle. Different types of such devices measure, in addition to volts, different units of voltage. In general, it is measured in the following units: millivolt, microvolt, kilovolt or megavolt.

Voltage value

The value of this parameter of electric current in our life is very high, because whether it corresponds to the required one depends on how brightly the incandescent lamps will burn in the apartment, and if compact fluorescent lamps are installed, then the question arises whether or not they will light at all. The durability of all lighting and household electrical appliances depends on its surges, and therefore having a voltmeter or multimeter at home, as well as the ability to use it, is becoming a necessity in our time.

Without some basic knowledge about electricity, it is difficult to imagine how electrical appliances work, why they work at all, why you need to plug in the TV to make it work, and why a flashlight only needs a small battery to shine in the dark.

And so we will understand everything in order.

Electricity

Electricity is a natural phenomenon that confirms the existence, interaction and movement of electric charges. Electricity was first discovered back in the 7th century BC. Greek philosopher Thales. Thales noticed that if a piece of amber is rubbed on wool, it begins to attract light objects. Amber in ancient Greek is electron.

This is how I imagine Thales sitting, rubbing a piece of amber on his himation (this is the woolen outerwear of the ancient Greeks), and then with a puzzled look he watches as hair, scraps of thread, feathers and scraps of paper are attracted to the amber.

This phenomenon is called static electricity. You can repeat this experience. To do this, rub a regular plastic ruler thoroughly with a woolen cloth and bring it to the small pieces of paper.

It should be noted that this phenomenon has not been studied for a long time. And only in 1600, in his essay “On the Magnet, Magnetic Bodies and the Great Magnet - the Earth,” the English naturalist William Gilbert introduced the term electricity. In his work, he described his experiments with electrified objects, and also established that other substances can become electrified.

Then, for three centuries, the most advanced scientists in the world researched electricity, wrote treatises, formulated laws, invented electrical machines, and only in 1897 Joseph Thomson discovered the first material carrier of electricity - the electron, a particle that makes electrical processes in substances possible.

Electron– this is an elementary particle, has a negative charge approximately equal to -1.602·10 -19 Cl (Pendant). Designated e or e –.

Voltage

To make charged particles move from one pole to another, it is necessary to create between the poles potential difference or - Voltage. Voltage unit – Volt (IN or V). In formulas and calculations, voltage is denoted by the letter V . To obtain a voltage of 1 V, you need to transfer a charge of 1 C between the poles, while doing 1 J (Joule) of work.

For clarity, imagine a water tank located at a certain height. A pipe comes out of the tank. Water under natural pressure leaves the tank through a pipe. Let's agree that water is electric charge, the height of the water column (pressure) is voltage, and the speed of water flow is electricity.

Thus, the more water in the tank, the higher the pressure. Similarly from an electrical point of view, the greater the charge, the higher the voltage.

Let's start draining the water, the pressure will decrease. Those. The charge level drops - the voltage decreases. This phenomenon can be observed in a flashlight; the light bulb becomes dimmer as the batteries run out. Please note that the lower the water pressure (voltage), the lower the water flow (current).

Electricity

Electricity is a physical process of directed movement of charged particles under the influence of an electromagnetic field from one pole of a closed electrical circuit to the other. Charge-carrying particles can include electrons, protons, ions and holes. Without a closed circuit, no current is possible. Particles capable of carrying electrical charges do not exist in all substances; those in which they exist are called conductors And semiconductors. And substances in which there are no such particles - dielectrics.

Current unit – Ampere (A). In formulas and calculations, current strength is indicated by the letter I . A current of 1 Ampere is generated when a charge of 1 Coulomb (6.241·10 18 electrons) passes through a point in an electrical circuit in 1 second.

Let's look again at our water-electricity analogy. Only now let’s take two tanks and fill them with an equal amount of water. The difference between the tanks is the diameter of the outlet pipe.

Let's open the taps and make sure that the flow of water from the left tank is greater (the diameter of the pipe is larger) than from the right. This experience is clear evidence of the dependence of flow speed on pipe diameter. Now let's try to equalize the two flows. To do this, add water (charge) to the right tank. This will give more pressure (voltage) and increase flow rate (current). In an electrical circuit, the pipe diameter is played by resistance.

The experiments carried out clearly demonstrate the relationship between voltage, electric shock And resistance. We'll talk more about resistance a little later, but now a few more words about the properties of electric current.

If the voltage does not change its polarity, plus to minus, and the current flows in one direction, then this is D.C. and correspondingly constant pressure. If the voltage source changes its polarity and the current flows first in one direction, then in the other, this is already alternating current And AC voltage. Maximum and minimum values (indicated on the graph as Io ) - This amplitude or peak current values. In home sockets, the voltage changes its polarity 50 times per second, i.e. the current oscillates here and there, it turns out that the frequency of these oscillations is 50 Hertz, or 50 Hz for short. In some countries, for example in the USA, the frequency is 60 Hz.

Resistance

Electrical resistance– a physical quantity that determines the property of a conductor to impede (resist) the passage of current. Resistance unit – Ohm(denoted Ohm or the Greek letter omega Ω ). In formulas and calculations, resistance is indicated by the letter R . A conductor has a resistance of 1 ohm to the poles of which a voltage of 1 V is applied and a current of 1 A flows.

Conductors conduct current differently. Their conductivity depends, first of all, on the material of the conductor, as well as on the cross-section and length. The larger the cross-section, the higher the conductivity, but the longer the length, the lower the conductivity. Resistance is the inverse concept of conductivity.

Using the plumbing model as an example, resistance can be represented as the diameter of the pipe. The smaller it is, the worse the conductivity and the higher the resistance.

The resistance of a conductor manifests itself, for example, in the heating of the conductor when current flows through it. Moreover, the greater the current and the smaller the cross-section of the conductor, the stronger the heating.

Power

Electric power is a physical quantity that determines the rate of electricity conversion. For example, you have heard more than once: “a light bulb is so many watts.” This is the power consumed by the light bulb per unit of time during operation, i.e. converting one type of energy into another at a certain speed.

Sources of electricity, such as generators, are also characterized by power, but already generated per unit of time.

Power unit – Watt(denoted W or W). In formulas and calculations, power is indicated by the letter P . For alternating current circuits the term is used Full power, unit - Volt-amps (VA or V·A), denoted by the letter S .

And finally about Electric circuit. This circuit is a certain set of electrical components capable of conducting electric current and interconnected accordingly.

What we see in this image is a basic electrical device (flashlight). Under voltage U(B) a source of electricity (batteries) through conductors and other components with different resistances 4.61 (244 Votes)