How to use a multimeter for beginners. Voltage measurement

General information

When climbing a mountain, we do work against the force of gravity

Since we live in the era of electricity, many of us are familiar with the concept of electrical voltage from childhood:

After all, sometimes, while exploring the surrounding reality, we received a considerable shock from him by secretly sticking a couple of fingers into the power socket of electrical devices, secretly from our parents.
Since you are reading this article, nothing particularly terrible has happened to you - it is difficult to live in the era of electricity and not become briefly acquainted with it. With the concept of electric potential,
the situation is somewhat more complicated.

Being a mathematical abstraction, the electric potential is best described by analogy by the action of gravity - the mathematical formulas are absolutely similar, except that negative gravitational charges do not exist, since mass is always positive and at the same time electric charges can be both positive and negative; Electric charges can both attract and repel. As a result of the action of gravitational forces, bodies can only attract, but cannot repel. If we could deal with negative mass, we would master antigravity.

But you just have to push off...

The concept of electric potential plays an important role in describing phenomena related to electricity. Briefly, the concept of electric potential describes the interaction of charges of different or identical signs or groups of such charges.

From the school physics course and from everyday experience, we know that when climbing a mountain, we overcome the force of gravity of the Earth and, thereby, do work against the forces of attraction acting in the potential gravitational field. Since we have some mass, the Earth tries to reduce our potential - to pull us down, which we gladly allow it, rapidly skiing and snowboarding. Similarly, an electric potential field tries to bring like charges closer together and repel like charges.

It follows from this that every electrically charged body tries to lower its potential by getting as close as possible to a powerful source of an electric field of the opposite sign, if no forces prevent this. In the case of charges of the same sign, each electrically charged body tries to lower its potential by moving as far as possible from a powerful source of electric field of the same sign, if no forces prevent this. And if they interfere, then the potential does not change - while you are standing on level ground at the top of the mountain, the force of the Earth’s gravitational attraction is compensated by the reaction of the support and nothing pulls you down, only your weight presses on your skis. But you just have to push off...

Similarly, the field created by some charge acts on any charge, creating the potential for its mechanical movement towards itself or away from itself, depending on the sign of the charge of the interacting bodies.

"Sisyphus", Titian, Prado Museum, Madrid, Spain

How to calculate your TV's electricity consumption

A TV is an essential element of household appliances in every home. Often, owners install several copies for each room. Devices can be of several types: cathode ray tube models, LED, LSD or plasma TVs. The power consumption of a device is affected by its type, screen size, color, brightness, white and black balance, active operation time, and duration of sleep mode. Based on the table of electricity consumption by household appliances, a TV uses an average of 0.1-0.3 kW.

Electrical energy consumption will depend on the type and operating mode of the TV.

The power of TVs in Watts with a cathode ray tube is 60-100 W per hour. On average he can work about 5 hours a day. Monthly consumption reaches 15 kW. This is how much electricity will be spent on its active operation. The TV also consumes 2-3 watts per hour in standby mode when plugged in. Total energy consumption can be 16.5-17.5 kW per month.

The energy consumption of LED or LSD models directly depends on the screen size. For example, an LSD TV with a 32-inch screen diagonal will consume 45-55 W per hour in operating mode, and 1 W in standby mode. The total electricity consumption per month is 6.7-9 kW. LED models consume on average 35-40% less electrical energy. In active mode, a 42-inch TV will use 80-100 W, in sleep mode - 0.3 W. Total consumption per month will be 15-20 kW.

Plasma TVs have good color reproduction. The TV power in kW is 0.15-0.19 in active mode, and 120 W/day in sleep mode. The total consumption per month can be 30-35 kW. To save energy, you should remove the plug from the socket, correctly adjust the brightness level depending on the time of day, and set the timer to automatically turn off.

Electric potential

A charge introduced into an electric field has a certain amount of energy, i.e., the ability to do work. To characterize the energy stored at each point of the electric field, a special concept was introduced - electric potential. The potential of the electric field at a given point is equal to the work that the forces of this field can do when moving a unit of positive charge from this point outside the field.

Returning to the analogy with the gravitational field, we can find that the concept of electric potential is akin to the concept of the level of various points on the earth's surface. That is, as we will consider below, the work of raising a body above sea level depends on how high we raise that body, and similarly, the work of moving one charge away from another depends on how far these charges are.

Let's imagine the hero of the ancient Greek world, Sisyphus. For his sins in earthly life, the gods sentenced Sisyphus to do hard, meaningless work in the afterlife, rolling a huge stone to the top of a mountain. Obviously, to lift a stone halfway up the mountain, Sisyphus needs to spend half as much work as to lift the stone to the top. Then the stone, by the will of the gods, rolled down the mountain, doing some work. Naturally, a stone raised to the top of a mountain of height H

(level H), when descending, will be able to do more work than a stone raised to level
H
/2. Sea level is generally considered to be the zero level, from which altitude is measured.

By analogy, the electrical potential of the earth's surface is considered zero potential, that is

ϕEarth = 0

where ϕEarth is the designation of the Earth’s electrical potential, which is a scalar quantity (ϕ is a letter of the Greek alphabet and is read as “phi”).

This quantity quantitatively characterizes the field’s ability to do work (W) to move some charge (q) from a given point in the field to another point:

ϕ = W/q

The SI unit of electrical potential is the volt (V).

Visitors to the Canadian Science and Technology Museum spin a large squirrel wheel, which spins a generator that powers a Tesla transformer (pictured right), which in turn creates a high voltage of several tens of thousands of volts, enough to puncture the air.

Voltage

One definition of electrical voltage describes it as the difference in electrical potential, which is given by the formula:

V = ϕ1 – ϕ2

The concept of voltage was introduced by the German physicist Georg Ohm

in a paper in 1827, which proposed a hydrodynamic model of electric current to explain Ohm’s empirical law discovered by him in 1826:

Tesla Transformer at the Canadian Science and Technology Museum

V = I R,

where V is the potential difference, I is the electric current, and R is the resistance.

Another definition of electric voltage is the ratio of the work done by the field to move a charge in a conductor to the magnitude of the charge.

For this definition, the mathematical expression for voltage is described by the formula:

V=A/q

Voltage, like electrical potential, is measured in volts

(V) and its decimal multiples and submultiples - microvolts (millionths of a volt, µV), millivolts (thousandths of a volt, mV), kilovolts (thousands of volts, kV) and megavolts (millions of volts, MV).

A voltage of 1 V is considered to be the voltage of an electric field that does 1 J of work to move a charge of 1 C. The dimension of voltage in the SI system is defined as

B = kg•m²/(A•s³)

Voltage can be created by various sources: biological objects, technical devices, and even processes occurring in the atmosphere.

Shark lateral line

The elementary cell of any biological object is a cell, which from the point of view of electricity is an electrochemical generator of low voltage. Some organs of living beings, such as the heart, which is a collection of cells, produce higher voltage. It is curious that the most advanced predators of our seas and oceans - sharks of various species - have a hypersensitive voltage sensor called the lateral line organ

, and allowing them to accurately detect their prey by heartbeat. Separately, it is perhaps worth mentioning electric stingrays and eels, which in the process of evolution have developed the ability to create voltages of over 1000 V to defeat prey and repel attacks on themselves!

Although people have been generating electricity, and thereby creating a potential difference (voltage), by rubbing a piece of amber on wool since ancient times, historically the first technical voltage generator was the galvanic cell

.
It was invented by the Italian scientist and doctor Luigi Galvani
, who discovered the phenomenon of potential difference arising when different types of metal and electrolyte come into contact.
This idea was further developed by another Italian physicist Alessandro Volta
.
Volta first placed plates of zinc and copper in acid to produce a continuous electric current, creating the world's first chemical current source. By connecting several of these sources in series, he created a chemical battery, the so-called “Volta Column
,” which made it possible to generate electricity using chemical reactions.

The Voltaic Pole is a replica made by an electrician at the Alessandro Volta Museum in Como, Italy. Canadian Science and Technology Museum in Ottawa

Due to his achievements in creating reliable electrochemical voltage sources, which played a significant role in further research into electrophysical and electrochemical phenomena, the unit of measurement of electrical voltage, the Volt, was named after Volt.

Among the creators of voltage generators, it is necessary to note the Dutch physicist Van der Graaff

, who created
a high-voltage generator
, which is based on the ancient idea of ​​​​separation of charges using friction - remember amber!

The fathers of modern voltage generators were two remarkable American inventors - Thomas Edison

and
Nikola Tesla
. The latter was an employee at Edison's company, but the two geniuses of electrical engineering disagreed on methods of generating electrical energy. As a result of the subsequent patent war, all of humanity won - Edison's reversible machines found their niche in the form of generators and DC motors, numbering in the billions of devices - just look under the hood of your car or just press the power window button or turn on the blender; and the methods of creating alternating voltage in the form of alternating current generators, devices for converting it in the form of voltage transformers and transmission lines over long distances and countless devices for its application rightfully belong to Tesla. Their number is in no way inferior to the number of Edison’s devices - fans, refrigerators, air conditioners and vacuum cleaners, and a host of other useful devices, the description of which is beyond the scope of this article, operate on Tesla principles.

Housed at the Canadian Science and Technology Museum in Ottawa, this motor-generator, manufactured by Westinghouse in 1904, was used as a reliable power source to generate the exciter magnetic field at a hydroelectric power station in Niagara Falls, NY. NY. The construction of the power plant was led by Nikola Tesla and George Westinghouse

Of course, scientists later created other voltage generators based on other principles, including the use of nuclear decay energy. They are designed to serve as a source of electrical energy for space envoys of humanity into deep space.

But the most powerful source of electrical voltage on Earth, not counting individual scientific installations, is still natural atmospheric processes.

Every second, over 2 thousand thunderstorms rumble on Earth, that is, tens of thousands of natural Van der Graaff generators operate simultaneously, creating voltages of hundreds of kilovolts, discharging currents of tens of kiloamperes in the form of lightning. But, surprisingly, the power of terrestrial generators cannot be compared with the power of electrical storms that occur on the Earth’s sister - Venus - not to mention huge planets like Jupiter and Saturn.

What is "watt"

This measurement unit belongs to the international classification SI and is a derivative. It is described as a power indicator at which 1 joule of energy is expended per second. It can also be given the following characteristic: it describes how quickly work is performed to maintain a constant speed of an object of 1 meter per second, forced to overcome the action of a force of 1 Newton, the vector of which is opposite to that of the moving body. To describe electromagnetic phenomena, the representation of a watt is also used as the rate of transformation of electricity with an electric current of 1 A flowing through a circuit fragment with a potential difference of 1 volt. An LED light bulb typically has a power consumption of several watts. Based on this, it should be clear that questions like “how many watts are in a volt” are irrelevant - these units describe completely different physical quantities.

In writing, the unit is usually denoted as “W” or “W”. The name itself was given by the name of the Scottish mechanic James Watt, who invented the steam engine. The unit was adopted for use in measuring power in 1882, and entered the SI system in 1960. Previously, the same quantities were usually measured in horsepower. A measuring device – a wattmeter – will help you find out the power parameters. For electrical appliances for professional or household use, the power consumption is indicated in the technical documentation attached to them, for example, in the device passport. On thyristors and other electronic components, the value is sometimes indicated by markings on the case.

James Watt

It is generally accepted that the total power value in practice, characterizing the actual load level introduced by the consumer to the components connected to the electrical network (switchboards, cable elements, transformer and other devices), is determined by the current consumption. Therefore, for transforming and switching devices, the power rating is described in the watt form, and not in the volt-ampere form.

Efficiency is also called power factor or cos fi. It is a dimensionless quantity that changes the current in accordance with the reactive component in the load. The coefficient illustrates the amount of alternating current passing through a phase shift relative to the applied voltage. The name cos fi denotes the cosine of a given phase shift.

An example is a hammer drill, the instructions for which indicate a consumption figure of 5 kW and a coefficient of 0.85. Then the full indicator required for its operation (in volt-amperes) will be equal to the quotient of these values: 5/0.85 = 5.89 kVA.

An electric kettle is an example of a device that does not have reactive power

Voltage characteristics

Voltage is characterized by its magnitude and shape. Regarding its behavior over time, a distinction is made between constant voltage (not changing over time), aperiodic voltage (changing over time) and alternating voltage (changing over time according to a certain law and, as a rule, repeating itself after a certain period of time). Sometimes, to achieve certain goals, the simultaneous presence of direct and alternating voltages is required. In this case, we talk about alternating current voltage with a constant component.

This voltmeter was used to measure voltage at the beginning of the 20th century. Canadian Science and Technology Museum in Ottawa

In electrical engineering, DC generators (dynamos) are used to create a relatively stable high-power voltage; in electronics, precision DC voltage sources are used on electronic components, which are called stabilizers

.

How to use an online calculator

Knowing the current parameters, you can independently calculate such an important parameter as power. This value determines the rate of energy consumption per unit of time, so you can calculate additional costs and load on the network when the device is turned on.

What information will you need to enter:

• Mains voltage, which may also vary. Car wiring is usually designed for 12 V voltage. On older models, the indicator is still 6 V, and on large vehicles - 24 V (buses or trucks with diesel engines).
• Rated current, the value of which can usually be found from the technical data sheet of the equipment. Typically, such information is placed directly on the device body.

The intuitive interface of the calculator will allow you to quickly convert amperes to kilowatts and perform other similar operations. The service will allow you to quickly convert the power consumption of electrical appliances in order to calculate the load on the network. In addition, such a calculator will provide car owners with complete information about the consumed power of the electrical network. This will allow you to easily select a new battery and replace individual electrical wiring components.

Voltage measurement

Voltage measurement plays an important role in fundamental physics and chemistry, applied electrical engineering and electrochemistry, electronics and medicine, and in many other branches of science and technology. It is perhaps difficult to find branches of human activity, excluding creative fields such as architecture, music or painting, where voltage measurements would not be used to control ongoing processes using various types of sensors, which are essentially converters of physical quantities into voltage. Although it is worth noting that in our time these types of human activities cannot do without electricity in general and without voltage in particular. Artists use tablets that measure the voltage of capacitive sensors when a stylus is moved over them. Composers play electronic instruments that measure the voltage on the key sensors and, depending on it, determine how hard a particular key is pressed. Architects use AutoCAD and tablets, which also measure voltage, which is converted into a numerical form and processed by a computer.

A kitchen thermometer (left) measures the temperature of meat by measuring the voltage across a resistive temperature sensor through which a small current is passed. In a multimeter (right), temperature is determined by measuring the voltage directly across the thermocouple

The measured voltage values ​​can vary widely: from fractions of a microvolt in studies of biological processes, to hundreds of volts in household and industrial devices and appliances, and up to tens of millions of volts in ultra-powerful particle accelerators. Voltage measurement allows us to monitor the condition of individual organs of the human body by taking encephalograms

brain activity.
Electrocardiograms
and
echocardiograms
provide information about the condition of the heart muscle. Using various industrial sensors, we successfully, and most importantly, safely, control chemical production processes, which sometimes occur at extreme pressures and temperatures. And even nuclear processes at nuclear power plants can be controlled by measuring voltages. Using stress measurements, engineers monitor the condition of bridges, buildings and structures and even withstand such formidable natural forces as earthquakes.

A pulse oximeter, like a voltmeter, measures the voltage at the output of a device that amplifies the signal from a photodiode or phototransistor. However, unlike a voltmeter, here on the display we see not the voltage value in volts, but the percentage of hemoglobin saturation with oxygen (97%).

The brilliant idea of ​​connecting different values ​​of voltage levels with the state values ​​of units of information gave impetus to the creation of modern digital devices and technologies. In computing, a low voltage level is interpreted as a logical zero (0), and a high voltage level is interpreted as a logical one (1).

In fact, all modern computing devices are, to one degree or another, voltage comparators (meters), converting their input states according to certain algorithms into output signals.

Among other things, accurate voltage measurements form the basis of many modern standards, the implementation of which guarantees their absolute compliance and thus safety of use.

The memory board used in personal computers contains tens of thousands of logic gates.

How to convert volts and watts and vice versa

To correctly complete the task associated with converting volts to watts, you can follow the following algorithm:

• You need to find the power value in the operating manual of the electrical appliance. Companies often indicate this value in volt-amperes. This symbol indicates the maximum amount of electricity consumed. So it is equal to the power value.
• Determine the efficiency of the power source based on the design features and the number of devices connected to it. As a rule, this coefficient is set in the range from 0.6 to 0.8.
• Convert current-voltage indicators to W: find out the active power of energy equipment designed to supply uninterruptible power.

You might be interested in Features of measuring illumination in lux

Important! Calculate the number of watts by multiplying volt-amperes by efficiency.

Visual representation of voltage and current

• Conversion from W to V follows the reverse pattern: watts must be divided by the efficiency factor.

When choosing a power source from the manufacturer, it is not always clear how much power the device produces. Therefore, it is recommended to study the technical parameters specified in the instructions in order to carry out the correct conversion from one value to another.

Voltage measuring instruments

In the course of studying and understanding the surrounding world, methods and means of measuring voltage have evolved significantly from primitive organoleptic methods

- Russian scientist Petrov cut off part of the epithelium on the fingers to increase sensitivity to the action of electric current - to the simplest voltage indicators and modern devices of various designs based on the electrodynamic and electrical properties of various substances.

The taste of electricity. Once upon a time, a long time ago, if there was no voltmeter, we determined the voltage with our tongue!

By the way, novice radio amateurs easily distinguished a “working” 4.5 V flat battery from a “dead” one without any devices due to their complete absence, simply by licking its electrodes. The electrochemical processes that took place gave a feeling of a certain taste and a slight burning sensation. Some outstanding individuals undertook to determine the suitability of even 9 V batteries in this way, which required considerable endurance and courage!

An example of the simplest indicator - a mains voltage probe - can be an ordinary incandescent lamp with an operating voltage not lower than the mains voltage. There are simple voltage probes available on sale using neon lamps and LEDs that consume low currents. Be careful, using homemade structures can be dangerous to your life!

It should be noted that devices for measuring voltage (voltmeters) differ greatly from each other, primarily in the type of voltage being measured - these can be direct or alternating current devices. In general, in measurement practice, the behavior of the measured voltage is important - it can be a function of time and have a different form - be constant, harmonic, non-harmonic, pulsed, and so on, and its value is usually used to characterize the operating modes of electrical circuits and devices (low-current and power).

The following voltage values ​​are distinguished:

• instant,
• amplitude,
• average,
• root mean square (rms).

The instantaneous voltage value Ui (see figure) is the voltage value at a certain point in time. It can be observed on the oscilloscope screen and determined for each moment in time using the oscillogram.

The amplitude (peak) voltage value Ua is the largest instantaneous voltage value over a period. Voltage swing Up-p is a value equal to the difference between the highest and lowest voltage values ​​over a period.

The root mean square (rms) voltage value Urms is defined as the square root of the squared average of the instantaneous voltage values ​​over the period.

All pointer and digital voltmeters are usually calibrated in rms voltage values.

The average value (constant component) of voltage is the arithmetic mean of all its instantaneous values ​​during the measurement time.

The average rectified voltage is defined as the arithmetic mean of absolute instantaneous values ​​over a period.

The difference between the maximum and minimum signal voltage values ​​is called the signal swing.

Nowadays, both multifunctional digital instruments and oscilloscopes are mainly used to measure voltage - their screens display not only the voltage shape, but also the essential characteristics of the signal. These characteristics also include the frequency of change of periodic signals, therefore, in measurement technology, the frequency limit of the measurement of the device is important.

Errors when calculating V•A

The ratios of volt amperes and watts for certain types of electrical appliances and devices, for example, light bulbs, are identical. But when talking about computers, watts and V•A will be different, but V•A will always be greater than or equal to watts. The gap is related to power factor (PF), which varies among devices. If you do not take it into account, then when selecting equipment elements an error will be made and they will not fit the main device.

If we consider the choice of a UPS for a personal computer, and on the passport data the rating is indicated in voltamper, this will make it difficult to select a rating in W. When there are no exact indicators of P, do the following - the load data indicated on the nameplate is taken equal to 60% of the V•A indicator of the UPS.

Online calculator

Additional Information. In order to more accurately determine the data, you can use an online calculator. Some websites provide the user with the required P if they click on the device type, such as TV or desktop. These sites often show graphical charts that make it easy to measure the V•A of various appliances, from refrigerators to computers.

It can be concluded that V•A is an important characteristic for modern electrical devices and equipment. If this indicator is not taken into account when purchasing electrical devices, they will operate in overload mode, which will lead to their premature failure.

Measuring voltage with an oscilloscope

An illustration of the above will be a series of experiments on measuring voltages using a signal generator, a constant voltage source, an oscilloscope and a multifunctional digital instrument (multimeter).

Experiment No. 1

The general scheme of experiment No. 1 is presented below:

The signal generator is loaded onto a load resistance R1 of 1 kOhm, and the measuring ends of an oscilloscope and a multimeter are connected in parallel to the resistance. When conducting experiments, we take into account the fact that the operating frequency of the oscilloscope is significantly higher than the operating frequency of the multimeter.

Experience 1:

Let us apply a sinusoidal signal from the generator with a frequency of 60 hertz and an amplitude of 4 volts to the load resistance. On the oscilloscope screen we will observe the image shown below. Note that the cost of dividing the scale grid of the oscilloscope screen along the vertical axis is 2 V. The multimeter and oscilloscope will show an rms voltage value of 1.36 V.

Experience 2:

Let's double the signal from the generator, the scope of the image on the oscilloscope will double exactly and the multimeter will show double the voltage value:

Experience 3:

Let's increase the generator frequency by 100 times (6 kHz), and the frequency of the signal on the oscilloscope will change, but the peak-to-peak and root-mean-square value will remain the same, and the multimeter readings will become incorrect - the permissible operating frequency range of the multimeter is affected: 0-400 Hz:

Experience 4:

Let's return to the original frequency of 60 Hz and the voltage of the signal generator 4 V, but change the shape of its signal from sine to triangular. The scope of the image on the oscilloscope remained the same, but the multimeter readings decreased compared to the voltage value that it showed in experiment No. 1, since the effective signal voltage changed:

Experiment No. 2

The design of experiment No. 2 is similar to the design of experiment 1.

Using the knob for changing the bias voltage on the signal generator, we will add a bias of 1 V. On the signal generator, we will set a sinusoidal voltage with a swing of 4 V with a frequency of 60 Hz - as in experiment No. 1. The signal on the oscilloscope will rise by half a major division, and the multimeter will show an rms value of 1.33 V. The oscilloscope will show an image similar to the image from experiment 1 of experiment #1, but raised by half a major division. A multimeter will show almost the same voltage as it was in experiment 1 of experiment No. 1, since it has a closed input, and an oscilloscope with an open input will show an increased effective value of the sum of direct and alternating voltages, which is greater than the effective value of the voltage without a constant component:

Multiples and submultiples [edit | edit code ]

For calculations involving power, it is not always convenient to use the watt itself. Sometimes, when the quantities being measured are very large or very small, it is much more convenient to use a unit of measurement with standard prefixes, which avoids constant calculations of the order of the value. Thus, when designing and calculating radars and radio receivers, pW or nW are most often used; for medical devices such as EEG and ECG, μW is used. In the production of electricity, as well as in the design of railway locomotives, megawatts (MW) and gigawatts (GW) are used.

The standard SI prefixes for watt are given in the following table.

Safety precautions when measuring voltage

Since, depending on the safety class of the room and its condition, even relatively low voltages of 12–36 V can pose a danger to life, the following rules must be followed:

1. Do not carry out voltage measurements that require certain professional skills (over 1000 V).
2. Do not measure voltages in hard-to-reach places or at heights.
3. When measuring voltages in a household network, use special means of protection against electric shock (rubber gloves, mats, boots or boots).
4. Use a proper measuring tool.
5. In the case of using multifunctional instruments (multimeters), ensure that the parameter being measured and its value are correctly set before measurement.
6. Use a measuring device with working probes.
7. Strictly follow the manufacturer's recommendations for using the measuring device.

Literature

Author of the article: Sergey Akishkin

How many volts are in 6 kV?

6 kV (6 kilovolts or 6 thousand volts, 6,000 V), 10 kV, 35 kV - this is the voltage class of the intra-city distribution network; disconnecting several such lines at once can “extinguish” at most a small city block, as a rule, the length of such lines is several kilometers .

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