Watt is a physical quantity that everyone has to deal with every day without even knowing it. What does it measure, when did it arise and by what formula can it be found? Let's find answers to all these questions.
What is watt
First of all, it is worth knowing the definition of this term. So, watt is a unit used in the International SI System.
It can be of three types:
- Mechanical.
- Electric.
- Thermal.
History of appearance
Watts were first used as a quantity to measure power in Great Britain in 1882. Before that, horsepower was in use, and their understanding differed in individual countries.
The inventor of this unit of measurement (watt) was the “father” of the industrial revolution - James Watt (sometimes spelled Watt). By the way, it was named after him. For this reason, both joule (named after the British scientist James Prescott Joule) and watt are always abbreviated with a capital letter - W (in English W).
Since 1960, the watt has been a unit of power used throughout the world. After all, it was then that he was recognized
Power formula
Having understood the definition and history of the appearance of the watt, it is worth finding out its formula. It looks like this: N = A/t. And this stands for work divided by time.
Sometimes, in order to find out the number of watts, a slightly different power formula is used: N = F x V. In this example, the required value is calculated not using work and time, but using force and speed data.
In fact, the second formula is a kind of adaptation of the classic one. It is simply taken into account that work is equal to the derivative of force by distance (A = F x S), and speed is the quotient of distance divided by time (V = S/t). If we put all this data: we get the following example: N = F x S/t = F x V.
Watts, Volts and Amps
In addition to the formula discussed in the previous paragraph for searching for the physical quantity being studied, there is another one. It demonstrates the relationship between power (watts) and current (amps).
However, before you read it, it's worth learning a little more about these units of measurement.
Volt (V, in English V) is a unit of measurement of electrical voltage. In formulas it is denoted by the Latin letter U.
Ampere (A, also A in English) is a quantity characterizing the strength of electric current, denoted by the letter I.
Formula for the relationship between power, voltage and current
Having briefly examined the features of all these quantities, we obtain this formula.
It looks like this: P = U x I. In it, P is power (watts), U is voltage (volts), I is current (amps).
If necessary, this formula can be simulated if the power is already known, but you need to find the current (I = P / U) or voltage (U = P / I).
With the modern development of technology, in order to find out how many watts are contained in a certain number of amperes, you can simply find a specialized power calculation program on the Internet and enter the available data into it. This is not difficult to do; in any search engine you need to look for the phrase “calculator for converting watts to amperes”, and the system will give the addresses of the necessary sites.
Sub-unit W
In addition to practical applications, the units in question are often used to perform numerous theoretical calculations. However, if the power is extremely low, writing watts using decimals with many zeros is quite impractical. To facilitate this task, scientists introduced sub-multiple W units. They are usually written as degrees with a minus.
To date, a dozen of them have been identified, but in practice many of them are not used.
For example, the first two submultiple units of a watt: dW (deciwatt, equal to 10 -1 W) and cW (centiwatt, equal to 10 -2 W) are not recommended for use. But milliwatt (mW, equal to 10 -3), microwatt (μW, equal to 10 -6) and nanowatt (nW, equal to 10 -9 W) are some of the most used. And not only in calculations, but also in the manufacture of various measuring instruments.
For example, in medical devices such as electrocardiographs and electroencephalographs, the units of measurement are microwatts (µW).
In addition to those listed above, there are five more sub-multiple units: picowatt (10 -12), femtowatt (10 -15), attowatt (10 -18), zeptowatt (10 -21) and ioctowatt (10 -24). However, all of them are used in rare cases, and then only in theoretical calculations.
Multiple units of W
The unit itself is relatively small. For example, to wash one kilogram of laundry in one hour in an A++ class automatic washing machine, you will need electricity. However, if you consider that on average about 3.5 kilograms of clothes are washed at the same time, this means that 525 W are consumed. And this is just one wash, but how many of them happen in a month or a year? Quite a lot, as well as the number of watts consumed. To make them easier to write, ten multiples of units are allocated based on W, written as powers.
As in the case of fractional values, the first two of them (decawatt - 10 1 and hectowatt - 10 2) are not usually used, so they exist only “de jure”.
It is worth noting that when writing abbreviations of multiple units, the first letters are often capitalized. This is done in order not to confuse megawatts (MW - 10 6) with microwatts (mW) and other similar quantities.
The most commonly used is the well-known kilowatt (kW). It is equal to a thousand watts (10 3). The second most popular is the aforementioned megawatt. This unit is most often used in the electrical power industry. Less commonly, it uses values such as gigawatts (GW - 10 9) and terawatts (TW - 10 12). For example, in one year on average, humanity consumes about 1.9 TW of electricity.
The remaining four quantities - petawatts (PW - 10 15), exawatts (EVt - 10 18), zettawatts (ZW - 10 21) and iotawatts (IW 10 24) - are very rarely used, mainly in theoretical calculations. For example, according to one of them, it is assumed that the total power of energy emitted by the Sun is 382.8 IW.
Despite the many multiples and sub-multiple units of the watt, it is not difficult to perform mathematical operations with them. The easiest way is to convert everything into watts and then perform operations with degrees.
Another simple way to find out watts (quantity when using large or small quantities associated with them) is to find an online calculator on the Internet. By the way, with its help you can even convert W into horsepower.
Watts and watt-hours
Having figured out what the unit of measurement is a watt (and also having learned its multiples and sub-multiple values and formulas for finding it), it is worth taking time to consider such a close concept as watt-hours (Wh). Although the names Watt and Wh are very similar, they represent slightly different concepts.
The second unit is used to measure the energy produced over a certain period of time (one hour).
To make the difference clearer, it is worth considering the operation of an ordinary electric kettle with a power of 2200 W. To prepare compotes for the winter, the housewife almost continuously heated water with it for one hour. During this time, the device used 2200 Wh. If a woman had taken a weaker 1100 W kettle, it would have boiled the same amount of liquid in two hours and would still have used the same 2200 Wh.
All electricity supplied to consumers is measured not in watts, but in watt-hours (usually in kilowatt-hours, also a ratio of one to a thousand). To confirm this, you can simply go to any house meter. Regardless of the country and manufacturer, the numbers (demonstrating the amount of electricity used) will be marked “kilowatt-hour” (kWh). It can also be in English: kilowatt-hour (kW⋅h).
Moreover, the power of any power plant that synthesizes it is measured in ordinary watts (kilowatts and megawatts).
Many of you have seen the difference in prices in domestic and Chinese online stores for high-power LEDs. A 50W model costs 100 rubles in China, 500 rubles in Russia. Externally they are similar, power consumption is the same, no differences are visible.
In fact, there are many technical characteristics that the Chinese use to make LEDs as cheap as possible. At the same time, both quality and parameters suffer greatly. But for a bad and cheap diode they don’t write real parameters, they indicate from high-quality LEDs. Usually they write the same standard 50,000 hours. services, the same power. Only ultra-bright white light LEDs of 100W, 50W, 30W, 20W, 10W will be considered. Infrared IR, Ultraviolet UV, RGB will be involved in separate reviews and tests.
- 1. Size
- 2. Parameters of ultra-bright LEDs
- 3. Characteristics from the Chinese
- 4. Example of characteristics from Bridgelux
- 5. Price
- 6. Variation of parameters
- 7. Base material
- 8. Conductors
- 9. The most powerful
- 10. Lenses for optics
Size
Sometimes the seller in the specifications for LEDs 10 W, 20 W, 30 W, 50 W, 100 W writes the size of the crystals used, in “mil” units. This is a unit of measurement equal to one thousandth of an inch, or 0.0254 millimeters. To check the seller's honesty, you can measure the size of the crystals with a micrometer. It just requires complete disassembly, removing the silicone coating and removing the phosphor layer.
LED matrices consist of standard 1-watt crystals, which are installed with single-wall panels in an emitter housing. Standard chip dimensions are 30*30mil and 45*45mil, in millimeters 0.762*0.762mm and 1.143*1.143mm. Rated current 300mA.
The exception is the 10W LED, it has 9 of them. Marketers added another one to increase sales.
Parameters of ultra-bright LEDs
To reduce the cost, the Chinese decided to install smaller and worse crystals at 10W, 20W, 30W, 50W, 100W at 0.5W and 0.75W, for which the rated current is 150mA and 220mA. For them, 300mA will be too much, they will degrade and overheat. Good crystals should range in size from 30*30mil to 45*45mil.
Matching size and power:
- 1W = 45*45mil;
- 1W = 30*30mil;
- 0.75W = 24*40mil;
- 0.5W = 24*24mil.
- 0.5W = 20*20mil for SMD5730
Bridgelux, Epistar, Epileds
Characteristics from the Chinese
A caring seller places a table with the parameters of LED matrices on the product page. If this data is not indicated, then I do not recommend buying from this place; there may be a wide variation in quality.
In the table for 24*24mil you can see that the seller indicates the standard power of 10W, 20W, 30W, 50W, 70W, 100W and the number of installed crystals. We carefully look at the voltage and current. For 100W the number of volts is 30-32V, Amperes 2-2.1A.
We calculate the power for24*24mil:
- minimum 30V*2A = 60W;
- maximum 32V*2.1A = 67.2W;
- that is, instead of the promised 100W, there will be 60-65W.
The value of 60-65W is still too high, since 1 chip is 0.5W, then in reality there is 50W, but they sold it to us as 100W. Crystals are already the cheapest and worst, so any overclocking is contraindicated for them.
We calculate for24*44mil:
- minimum 30V * 2.850A = 85.5W;
- maximum 32V * 3A = 96W;
- the average will be 90W.
According to the table, we got 90W, in reality it was 75W, we increased it by 15W.
Let's calculate for 30*30mil:
- minimum 32V * 2.8A = 89.6W
- maximum 34V * 3.5A = 119W
- average 105W
The 30*30mil size delivers the promised specifications. The same chips are installed in regular high-quality 1W single-wall units with power consumption of 10W, 20W, 30W, 50W, 70W, 100W
Example characteristics from Bridgelux
I will show you the characteristics of powerful LED COB matrices from global manufacturers. Use this table to compare with budget ones. The luminous flux depends on the color temperature, the higher it is, the better the Lumen per Watt efficiency. It also depends on the color rendering index, with CRI70 the light output is up to 128 lm/W.
The difference in these parameters for the same power, for example 50W, is:
- CRI90, 2700K, 50W = 80 lm/W;
- CRI70, 5600K, 50W = 128 lm/W;
- 128lm/W - 80lm/W = 48lm/W difference, or 60%.
Price
The most interesting thing remains, this is the price of such products for 10W, 20W, 30W, 50W, 100W. I will indicate the prices in rubles at which I bought them. As you can see, the price differs by 3-4 times. When buying cheap junk, don’t hope for a miracle that you’ll be lucky and get a good one. The only way to operate for a long time is to use a low current. In this way, active degradation and unnecessary heating can be avoided.
| Energy consumption | 24*24mil | 24*44mil | 30*30mil |
| 10W | 33 rub. | 20 rub. | 129 rub. |
| 20W | 78 | 63 | 226 |
| 30W | 98 | 82 | 278 |
| 50W | 131 | 107 | 302 |
| 70W | 150 | — | |
| 100W | 205 | 121 rub. | 453 |
At most, such chips can be heated to 60° and this is the temperature of the crystal, not the case. The critical temperature will be 70°. For powerful branded ones, heating is allowed up to 110°, for the highest quality and most expensive ones up to 150°.
The luminous flux, of course, is quite high, the Chinese promise 100 lm/W. In reality it varies from 60 to 80lm/W. For a high-quality branded one, this indicator is 105-120 lm/W.
This information can be used to get a refund for an item. You were deceived if the real power turns out to be 2 times less. We open a dispute on Aliexpress and ask for a refund of half the amount. Two weeks ago I bought these diodes for 2000 rubles. They will come soon and I will ask for compensation for the deception.
Variation of parameters
Cheap LED chips of 10, 20, 50, 100 watts can have quite large differences in parameters. Because of this, some chips will heat up more and degrade, and accordingly they will fail faster. To check, turn them on at a very low current so that they glow a little. Visually, you will see that some crystals shine strongly and others poorly.
Base material
To reduce the cost, the Chinese use aluminum or its alloys as the base material. High-quality ones use copper, which has better thermal conductivity. Therefore, a high-quality, powerful LED should weigh 2-3 more than a cheap one.
Conductors
To connect crystals to contacts, thin threads in quantities of 2 to 4 pieces are used. And here you can save money by replacing 4 gold threads with copper ones or reducing the quantity to 2 pieces. Another option is a copper thread coated with gold on top; it is very difficult to tell the difference.
They are responsible for the current strength at which the diode can operate. They are made with a reserve to withstand power surges and not burn out. On budget matrices there are fewer of them or they are made of copper.
Some of you have already encountered a similar phenomenon with LED marker lamps. A Chinese light bulb with a power stabilizer will work less hours than a lamp with branded diodes without a stabilizer. The brand has high-quality conductors that can withstand surges in the automotive network, which can be up to 30V.
The most powerful
In addition to the common 10 W, 20 W, 30 W, 50 W, 100 W LEDs, there are also the most powerful LEDs at 150W, 300W, 500W. According to the test results, the luminous flux in the presence of optics on a 500-watt diode melts snow at a distance of several meters. Due to the large size of the installed crystals, very fat and heated photons fly out of them.
Lenses for optics
When making LED spotlights and lamps, the most difficult thing is to find a suitable housing that will focus, protect, and cool. Usually a radiator and driver are available as the basis of the design. One of the easiest ways to cover a powerful LED and focus its light output is to install a collimator lens. The kit consists of a chrome frame, reflector and lens. Light focusing can be from 5° to 90°. It is enough to fix the LED on any radiator and close it from above. It will be completely protected from external influences, in case the crows peck it out.
10 W LED is a powerful semiconductor device. The scope of its application is often not limited to lamps and spotlights. The chip is also very popular among those who like to make their own lighting devices.
Application area
10 W are widely used in various lighting devices. All areas can be divided into general and special purposes. General purpose includes the use of LEDs in lamps, luminaires, spotlights, and special purpose includes use for lighting in greenhouses and. The second option is the so-called, and not only. The trick is that the emission spectrum of this LED is optimal for plant growth, both on land and in water. And in addition to algae and fish, lighting with 10-watt LEDs has a beneficial effect on the development of corals, so aquarium lovers are frequent consumers of this radio component. All these wonderful properties are manifested in a certain combination of crystal colors. As for the use of the described semiconductor device for general-purpose lighting devices, in addition to household lamps, LEDs are excellently used for making car headlights, traffic lights, and road lighting.
LED design, design options
The COB 10 W LED is a compact module made using chip-on-board technology. The fundamental difference from SMD is that several crystals are placed together on the board and covered with a common layer of phosphor. This significantly reduces the cost of the matrix. It consists of 9 crystals: three parallel chains of three serially connected crystals in each. Externally, LED 10 W may differ in the shape of the conductive substrate. For example, the company's LED looks as shown in the figure. Its substrate is star-shaped and made of aluminum.
The module body is made of heat-resistant plastic, and the lens is made of epoxy resin. Classic LED 10 W looks as shown in the diagram, but in practice the overall dimensions vary depending on the manufacturer.
Do not forget that the LED is a polar element, so pay attention to the markings when installing. A prerequisite for adequate functioning of a 10 W LED is the presence of a heat sink. It can be organized using an aluminum or copper radiator. Lubricate the LED substrate with thermal conductive paste or hot melt adhesive for better heat transfer. Sometimes a cooler is additionally installed, which provides air circulation to cool the radiator fins.
In the video you can see a test of a 10W LED and recommendations for connecting such an element. Here's what the 10W LED wiring diagram should look like.
The power source can be a car battery, a computer power supply, or a specially purchased 12-volt source. In order to avoid overheating (despite the heatsink) and protect the LED, it is imperative to connect it not directly to the source, but through any voltage stabilizer. The diagram shows an LM-317 integrated voltage stabilizer, but another one with suitable parameters can be used. With the help of a regular cable and a resistor, you will provide yourself with a guaranteed 12 V output and the current will not exceed 1 A, which is the key to the longevity of your device.
Characteristics
The parameters of the 10-watt LED allow it to be in great demand in the line of super-bright LEDs. The supply voltage ranges from 9 to 12 Volts. The glow angle is 120° – the graph is shown below.
The rated forward current is 1 A, the pulsating forward current is up to 2 A. The luminous flux is in the range of 600-1080 lm. For comparison, a 75 W incandescent lamp produces a glow of 935 lm. Thus, you can roughly estimate how bright the glow of a given semiconductor device will be. The reverse voltage is 50 V., depending on the manufacturer, 30-100 thousand hours. Operating temperature ranges from -30°C to 80°C. The color temperature of a 10W LED covers the spectrum from 2300K (warm white) to 10000K (cool white).
Manufacturers
The leaders in the production of high-power LEDs, such as LED 10 W, are dispersed in three parts of the world. Among them are the American company Cree (which we have already mentioned and demonstrated a sample of its products), the Japanese Nichia (a pioneer in the field of LED technology), and also the German Osram (more known to domestic buyers).
Branded LED products are more expensive than their noname counterparts, but in the second case no one guarantees quality.
Let's consider what features you will encounter if you decide to purchase Chinese cheap 10-watt LEDs. Firstly, if you compare carefully, the 9 matrix crystals themselves are smaller in size than those of high-quality modules. This will naturally affect the light output during their operation. Secondly, the strong unevenness of the glow of each crystal. This is noticeable, however, only at a reduced current, but, nevertheless, this feature affects the degradation rate of the entire LED module.
10 watt fakes from China
In the picture you can observe the uneven glow of individual crystals of the module, and how it levels out with increasing current. Thirdly, in low-quality LEDs, the conductors connecting the crystals are very thin and can break due to careless movement, which will interrupt the functioning of at least one triple of successive crystals.
Summarizing what was described above, I would like to highlight the important points of the article for memorization. 10 W LEDs as light-emitting sources are widely used in practice for the manufacture of car lamps, flashlights, spotlights and other lighting devices. Heatsink cooling is critical for proper LED performance. Power is supplied from a 12V source through a driver (voltage stabilizer). A well-known brand guarantees uninterrupted operation for the entire stated period, but problems may arise with Chinese inexpensive analogues.
Naturally, you understand that the design of this LED is not intended to dissipate such a large power. During the experiments, already half a watt caused a slight heating of the case.
Technical parameters of the Cree XM-L-H LED are indicated on the website.
XMLAWT-0-1A0-T60-00-0001
- 1000-Lumen ultra bright white light output
- Working voltage: 3.0~3.5V
- Working current: 3000mA
- Aluminum plate: 20mm
First of all, let’s take the current-voltage characteristic of the specified LED device and enter the results into the table.
| LED voltage | 2,3 | 2,4 | 2,5 | 2,57 | 2,63 | 2,72 | 2,81 | 2,95 3,1 |
| LED current, mA | 1 | 10 | 50 | 100 | 250 | 500 | 1000 | 2000 3000
|
As you can see, the slope of the current-voltage characteristic is quite high, and a small voltage deviation within 0.1V immediately leads to a sharp change in current consumption. And given that the operating current reaches 3 amperes, the use of a quenching resistor to stabilize the current is no longer necessary. After all, for a normal power supply of 10 watts, let’s say from a 12V car battery, you would have to install a 3 Ohm resistor with a power of 35 watts!
So in this case, there is no alternative to using a special converter-driver. Moreover, its price is within 2-4e.
Now let’s test the LED in a duel with a 220V 60W incandescent light bulb. The photos below show lighting options with both light sources.
10 watt LED only
60 watt incandescent lamp only
Draw your own conclusions. Of course, the LED is inferior in color temperature (after all, 6000K), but in terms of brightness per watt of power consumption it is several times superior to its rival.
Another good feature is the very wide angle of light, almost 170 degrees. Gone is the era of LEDs with lenses; now you don’t even need a reflector to get normal lighting. The design of the light emitter of the LED device is such that light is emitted evenly over the entire hemisphere.
It seems interesting to use this 10-watt one either in a powerful LED flashlight (which was done), or together with an LED driver in the body of a burnt-out fluorescent energy-saving lamp. But do not forget about sufficient heat dissipation - the radiator dimensions must be at least 10 square meters. cm.
I won’t talk about the price of an LED, since the cost of LED devices is constantly decreasing. Check in online stores. In the following articles we will conduct interesting experiments with a powerful LED of several tens of watts!
Discuss article 10 W LEDs
In 1882, the British Scientific Association decided to start using a new unit of measurement called the "watt". What is it used for today, what is it equal to and by what formula can it be calculated? Let's find answers to all these questions.
Watt is a unit of measurement for what?
Since that fateful year when the British introduced the tradition of using the watt, gradually the whole world began to switch to it, replacing the outdated and impractical horsepower. With the advent of the SI system, it was included in it and began to be used everywhere.
So, what physical quantity has the unit of measurement “watt”? Let's remember our physics lessons: the correct answer to this question is power.
The watt received its name in honor of its “father” - the Scotsman James Watt. In abbreviation, this unit is always written with a capital letter - W (W - according to the international standards of the SI system), and in full - with a small “watt” (watt).
Being not a basic, but a derived unit (according to the SI standard), the unit in question is dependent on the meter, kilogram and second. In practice, this means that one watt is the power at which one joule of work is performed in one second of time. That is, the following relationship is obtained: 1W = 1J/1s = 1N x m/s = kg x m 2 / s 3 = kg x m 2 x s -3.
In addition to those listed above, the watt is associated with non-systemic units. For example, with calories. So 1 W = 859.845227858985 cal/hour. This ratio is important when it comes to calculating the amount of heat generated by an electric heater.
Formula
So, watt is a unit of power. Let's look at what formula can be used to calculate it.
As mentioned above, power depends on work and time. The following formula is obtained: P = A/t (power is equal to the quotient of work divided by time).
Knowing that the work formula is equal to: A = F x S (where F is force, S is distance), you can use this data.
As a result, we obtain the formula: P = F x S /t. And since S /t is speed (V), then power can be calculated like this: P = F x V
Relationship between ampere, watt and volt
The unit of measurement we are considering is directly related to quantities such as voltage (measured in volts) and current (measured in amperes).
1 watt is the power of direct electric current at a voltage of 1 V and a force of 1A.
In the form of a formula, it looks like this: P = I x U.
Watts, kilowatts, megawatts and microwatts
Having learned that a watt is a unit of measurement of power, on what quantities it depends and what formulas are easier to calculate it by, you should pay attention to such concepts as kilowatt, megawatt and microwatt.
Since W is a very modest value (this is the transmitter power of any mobile phone), in the electricity sector it is more common to use kilowatts (kW).
Judging by the standard “kilo” prefix for the SI system, we can conclude that 1 kW = 1000 W = 10 3 W. Therefore, to convert watts to kilowatts, you simply need to divide their number by a thousand, or vice versa, if kilowatts are converted to watts.
For example, a typical passenger car has a power of 60,000 watts. To convert this to kilowatts, you divide 60,000 by 1000 and the result is 60 kW.
Kilowatts are a common unit for measuring electrical power. In this case, a larger multiple of the watt unit is sometimes used. We are talking about a megawatt - MW. It is equal to 1,000,000 watts (10 6) or 1000 kilowatts (10 3).
For example, the British Eurostar electric train has a capacity of 12 megawatts. That is, this is 12,000,000 watts. No wonder it is the fastest in the UK.
Despite its modest size, sometimes this unit turns out to be too large to measure the power of certain objects, therefore, along with multiples, sub-multiple units of watt are also distinguished in the C system. The most commonly used of these is the microwatt (μW - written with a lowercase letter to avoid confusion with megawatt). It is equal to one millionth of a watt (10 -6). Typically, this unit is used when calculating the power of electrocardiographs.
In addition to the three listed above, there are about two dozen other multiples and sub-multiples of the watt. However, they are most often used in theoretical calculations rather than in practice.
Watt hour
Considering the features of a watt (a unit of measurement of power), let's pay attention to the watt-hour (Wh). This term is used to measure a quantity such as energy (sometimes work is measured in watt-hours).
1 watt-hour is equal to the amount of work performed for one hour at a power of 1 watt.
Since the unit in question is quite small, the kilowatt-hour (kWh) is most often used to measure electricity. It is equal to 1000 watt-hours or 3600 W·s.
Please note that the power generated at power plants is measured in kilowatts (sometimes megawatts), but for consumers its amount is calculated in kilowatt hours (less often in megawatt hours if we are talking about megacities or huge enterprises).
Note that in addition to the kilowatt-hour and megawatt-hour, the watt-hour has exactly the same multiples and sub-multiple units as the regular watt.
What device is called a wattmeter?
After comparing the definition of a watt (a unit of power) and a watt-hour (a unit of energy or work), pay attention to a device such as a wattmeter (wattmeter). It is used to measure the active power of electric current.
A classic device of this kind consists of four contacts, two of which are used to connect the wattmeter to the electrical circuit in series with that part of it whose power consumption is currently being measured. The remaining two contacts are connected in parallel to it.
Wattmeters are usually created on the basis of electrodynamic mechanisms.
