The standard inductor design consists of an insulated wire with one or more strands wound in a spiral around a dielectric frame that is rectangular, cylindrical, or shaped. Sometimes, coil designs are frameless. The wire is wound in one or more layers.
In order to increase the inductance, cores made of ferromagnets are used. They also allow you to change the inductance within certain limits. Not everyone fully understands why an inductor is needed. It is used in electrical circuits as a good direct current conductor. However, when self-induction occurs, resistance arises that prevents the passage of alternating current.
Types of inductors
There are several design options for inductors, the properties of which determine the scope of their use. For example, the use of loop inductors together with capacitors makes it possible to obtain resonant circuits. They are characterized by high stability, quality and precision.
Coupling coils provide inductive coupling of individual circuits and stages. Thus, it becomes possible to divide the base and circuits by direct current. High precision is not required here, therefore, these coils use a thin wire wound in two small windings. The parameters of these devices are determined in accordance with inductance and coupling coefficient.
Some coils are used as variometers. During operation, their inductance can change, which allows you to successfully rebuild the oscillatory circuits. The entire device includes two coils connected in series. The moving coil rotates inside the stationary coil, thereby creating a change in inductance. In fact, they are a stator and a rotor. If their position changes, then the value of self-induction will change. As a result, the inductance of the device can change by 4-5 times.
In the form of chokes, those devices are used that have high resistance with alternating current, and very low resistance with constant current. Due to this property, they are used in radio engineering devices as filter elements. At a frequency of 50-60 hertz, transformer steel is used to make their cores. If the frequency is higher, then the cores are made of ferrite or permalloy. Certain types of chokes can be seen in the form of so-called barrels, which suppress interference on the wires.
Where are inductors used?
The scope of application of each such device is closely related to the features of its design. Therefore, it is necessary to take into account its individual properties and technical characteristics.
Together with resistors or, coils are used in various circuits that have frequency-dependent properties. First of all, these are filters, oscillatory circuits, feedback circuits, etc. All types of these devices contribute to the accumulation of energy, the transformation of voltage levels in a pulse stabilizer.
When two or more coils are inductively coupled to each other, a transformer is formed. These devices can be used as electromagnets, and also as an energy source that excites inductively coupled plasma.
Inductive coils are successfully used in radio engineering, as an emitter and receiver in ring designs and those working with electromagnetic waves.
Welcome everyone to our website!
We continue to study electronics from the very beginning, that is, from the very basics, and the topic of today’s article will be operating principle and main characteristics of inductors. Looking ahead, I will say that first we will discuss theoretical aspects, and several future articles will be devoted entirely to consideration of various electrical circuits that use inductors, as well as elements that we studied earlier in our course - and.
The design and principle of operation of an inductor.
As is already clear from the name of the element, an inductor, first of all, is just a coil :), that is, a large number of turns of an insulated conductor. Moreover, the presence of insulation is the most important condition - the turns of the coil should not short-circuit with each other. Most often, the turns are wound on a cylindrical or toroidal frame:
The most important characteristic inductors is, naturally, inductance, otherwise why would it be given such a name :) Inductance is the ability to convert the energy of an electric field into the energy of a magnetic field. This property of the coil is due to the fact that when current flows through the conductor, a magnetic field appears around it:
And here’s what the magnetic field that appears when current passes through the coil looks like:
In general, strictly speaking, any element in an electrical circuit has inductance, even an ordinary piece of wire. But the fact is that the magnitude of such inductance is very insignificant, in contrast to the inductance of coils. Actually, in order to characterize this value, the Henry (H) unit of measurement is used. 1 Henry is actually a very large value, so µH (microhenry) and mH (milihenry) are most often used. Size inductance coils can be calculated using the following formula:
Let's figure out what kind of value is included in this expression:
It follows from the formula that as the number of turns or, for example, the diameter (and, accordingly, the cross-sectional area) of the coil increases, the inductance will increase. And as the length increases, it decreases. Thus, the turns on the coil should be placed as close to each other as possible, since this will lead to a decrease in the length of the coil.
WITH inductor device We've figured it out, it's time to consider the physical processes that occur in this element when an electric current passes. To do this, we will consider two circuits - in one we will pass direct current through the coil, and in the other - alternating current :)
So, first of all, let's figure out what happens in the coil itself when current flows. If the current does not change its value, then the coil has no effect on it. Does this mean that in the case of direct current the use of inductors should not be considered? But no :) After all, direct current can be turned on/off, and it’s at the moments of switching that all the most interesting things happen. Let's look at the circuit:
In this case, the resistor acts as a load; in its place there could be, for example, a lamp. In addition to the resistor and inductance, the circuit includes a DC source and a switch with which we will close and open the circuit.
What happens the moment we close the switch?
Coil Current will begin to change, since at the previous moment in time it was equal to 0. A change in current will lead to a change in the magnetic flux inside the coil, which, in turn, will cause the occurrence of EMF (electromotive force) of self-induction, which can be expressed as follows:
The occurrence of EMF will lead to the appearance of an induced current in the coil, which will flow in the direction opposite to the direction of the power source current. Thus, the self-induced emf will prevent current from flowing through the coil (the induced current will cancel the circuit current due to the fact that their directions are opposite). This means that at the initial moment of time (immediately after closing the switch) the current through the coil will be equal to 0. At this moment in time, the self-induction EMF is maximum. What will happen next? Since the magnitude of the EMF is directly proportional to the rate of change of current, it will gradually weaken, and the current, accordingly, on the contrary, will increase. Let's look at graphs that illustrate what we've discussed:
In the first graph we see circuit input voltage– the circuit is initially open, but when the switch is closed, a constant value appears. In the second graph we see change in current through the coil inductance. Immediately after closing the switch, the current is absent due to the occurrence of self-induction EMF, and then begins to gradually increase. The voltage on the coil, on the contrary, is at its maximum at the initial moment of time, and then decreases. The voltage graph across the load will coincide in shape (but not in magnitude) with the current graph through the coil (since in a series connection the current flowing through different elements of the circuit is the same). Thus, if we use a lamp as a load, they will not light up immediately after closing the switch, but with a slight delay (in accordance with the current graph).
A similar transient process in the circuit will be observed when the key is opened. A self-inductive emf will arise in the inductor, but the induced current in the event of an open circuit will be directed in the same direction as the current in the circuit, and not in the opposite direction, therefore the stored energy of the inductor will be used to maintain the current in the circuit:
After the switch is opened, a self-induction emf occurs, which prevents the current through the coil from decreasing, so the current does not reach zero immediately, but after some time. The voltage in the coil is identical in shape to the case of closing the switch, but opposite in sign. This is due to the fact that the change in current, and accordingly the self-inductive emf in the first and second cases, is opposite in sign (in the first case, the current increases, and in the second it decreases).
By the way, I mentioned that the magnitude of the self-induction EMF is directly proportional to the rate of change of current, so the proportionality coefficient is nothing more than the inductance of the coil:
This concludes with inductors in DC circuits and moves on to AC circuits.
Consider a circuit in which alternating current is supplied to the inductor:
Let's look at the dependences of current and self-induction EMF on time, and then we'll figure out why they look like this:
As we have already found out Self-induced emf we have a directly proportional and opposite sign of the rate of change of current:
Actually, the graph shows us this dependence :) See for yourself - between points 1 and 2 the current changes, and the closer to point 2, the smaller the changes, and at point 2 for a short period of time the current does not change at all its meaning. Accordingly, the rate of change of current is maximum at point 1 and smoothly decreases as it approaches point 2, and at point 2 it is equal to 0, which is what we see in self-induced emf graph. Moreover, over the entire interval 1-2, the current increases, which means the rate of its change is positive, and therefore the EMF across this entire interval, on the contrary, takes negative values.
Similarly, between points 2 and 3 - the current decreases - the rate of change of the current is negative and increases - the self-induction emf increases and is positive. I won’t describe the remaining sections of the graph - all processes there proceed according to the same principle :)
In addition, on the graph you can notice a very important point - with increasing current (sections 1-2 and 3-4), the self-induction EMF and current have different signs (section 1-2: , title="Rendered by QuickLaTeX.com" height="12" width="39" style="vertical-align: 0px;">, участок 3-4: title="Rendered by QuickLaTeX.com" height="12" width="41" style="vertical-align: 0px;">, ). Таким образом, ЭДС самоиндукции препятствует возрастанию тока (индукционные токи направлены “навстречу” току источника). А на участках 2-3 и 4-5 все наоборот – ток убывает, а ЭДС препятствует убыванию тока (поскольку индукционные токи будут направлены в ту же сторону, что и ток источника и будут частично компенсировать уменьшение тока). И в итоге мы приходим к очень интересному факту – катушка индуктивности оказывает сопротивление переменному току, протекающему по цепи. А значит она имеет сопротивление, которое называется индуктивным или реактивным и вычисляется следующим образом:!}
Where is the circular frequency: . - This .
Thus, the higher the frequency of the current, the greater the resistance the inductor will provide to it. And if the current is constant (= 0), then the reactance of the coil is 0, accordingly, it has no effect on the flowing current.
Let's go back to our graphs that we made for the case of using an inductor in an AC circuit. We have determined the self-induction emf of the coil, but what will the voltage be? Everything here is actually simple :) According to Kirchhoff’s 2nd law:
And consequently:
Let's plot the dependence of current and voltage in the circuit on time on one graph:
As you can see, the current and voltage are shifted in phase () relative to each other, and this is one of the most important properties of alternating current circuits in which an inductor is used:
When an inductor is connected to an alternating current circuit, a phase shift appears in the circuit between voltage and current, with the current being out of phase with the voltage by a quarter of a period.
So we figured out how to connect the coil to the AC circuit :)
This is where we will probably finish today’s article; it has already turned out to be quite lengthy, so we will continue our conversation about inductors next time. So see you soon, we will be glad to see you on our website!
Option I
1. Who discovered the phenomenon of electromagnetic induction?
a) X. Oersted; b) Sh. Pendant;
c) A. Volta; d) A. Ampere;
d) M. Faraday; e) D. Maxwell.
2. The copper wire coil leads are connected to the sensitive
EMF of electromagnetic induction in a coil?
a permanent magnet is inserted into the coil;
a permanent magnet is removed from the coil;
a permanent magnet rotates around its longitudinal axis inside the coil.
a) only in case 1; b) only in case 2;
c) only in case 3; d) in cases 1 and 2;
e) in cases 1, 2 and 3.
3. What is the name of a physical quantity equal to the product of the modulusIN
magnetic field induction per areaSsurface penetrated by magic
thread field, and the cosine of the angleα
between vectorINinduction and normal
nto this surface?
a) inductance; b) magnetic flux;
c) magnetic induction; d) self-induction;
e) magnetic field energy.
4. What is the name of the unit of measurement of magnetic flux?
a) Tesla; b) Weber;
5. At points 1. 2. 3 the location of the magnetic needles is shown (Fig. 68). Draw how the magnetic induction vector d) Henry is directed at these points. At points 1, 2, 3 the location of the magnetic needles is shown (Fig. 68). Draw how the magnetic induction vector is directed at these points.
6 Magnetic lines The field inductions go from left to right parallel to the plane of the sheet, the current-carrying conductor is perpendicular to the plane of the sheet, and the current is directed into the plane of the notebook. The vector of the Ampere force acting on the conductor is directed...
a) to the right; b) left;
c) up; d) down.
Option II
1. What is the name of the phenomenon of the occurrence of electric current in a closed circuit?
that circuit when the magnetic flux through the circuit changes?
a) electrostatic induction; b) the phenomenon of magnetization;
c) Ampere force; d) Lorentz force;
e) electrolysis; e) electromagnetic induction.
2.
The leads of a coil of copper wire are connected to the sensitive
galvanometer. In which of the following experiments will the galvanometer detect
the occurrence of electromagnetic induction emf in the coil?
a permanent magnet is inserted into the coil;
the coil is placed on a magnet;
The coil rotates around a magnet located inside it.
a) in cases 1, 2 and 3; b) in cases 1 and 2;
c) only in case 1; d) only in case 2;
d) only in case 3.
3. Which of the following expressions determines magnetic flux?
a) BS cosα b) ∆Ф/∆t
B)qVBsinα; d) qVBI;
e) IBl sin α.
4. The unit of change of which physical quantity is 1 weber?
a) magnetic field induction; b) electrical capacity;
c) self-induction; d) magnetic flux;
d) inductance.
5. Draw a picture of the magnetic induction lines at
current flowing through a coil (Fig. 69) wound on
cardboard cylinder. How will this picture change if:
a) increasing the current in the coil?
b) reducing the number of turns wound on the coil?
c) inserting an iron core into it?
6. The current-carrying conductor lies in the plane of the sheet. A current passes through the conductor from below, and an Ampere force directed from the sheet acts upward on it. This can happen if the north pole of a bar magnet is brought...
a) on the left; b) on the right;
c) from the front side of the sheet; d) on the reverse side of the sheet.
When manufacturing metal detectors of any type, special attention should be paid to the quality of the search coil (coils) and its precise tuning to the operating search frequency. The detection range and stability of the generation frequency greatly depend on this. It often happens that with a correct and fully operational circuit, the frequency “floats”, which can, of course, be explained by the temperature instability of the elements used (mainly capacitors). I have personally assembled more than a dozen different metal detectors, and in practice, the temperature stability of passive elements still does not provide guaranteed frequency stability if the search coil itself is made carelessly and its precise tuning to the operating frequency is not ensured. Next, practical recommendations will be given on the manufacture of high-quality sensor coils and their configuration for single-coil metal detectors.Making a good reel
Typically, metal detector coils are wound “in bulk” on some kind of mandrel - a pan, a jar, etc. suitable diameter. Then they wrap it with electrical tape, shielding foil and again with electrical tape. Such coils do not have the necessary structural rigidity and stability, are very sensitive to the slightest deformation and greatly change the frequency even with simple squeezing with your fingers! A metal detector with such a coil will have to be adjusted every now and then, and the control knob will constantly leave your fingers with big sore calluses :). It is often recommended to “fill such a coil with epoxy,” but where should one fill it, epoxy, if the coil is frameless?.. I can offer a simple and easy way to make a high-quality coil, sealed and resistant to all kinds of external influences, with sufficient structural rigidity and, moreover, the same, providing simple attachment to a stick-bar without any brackets.
For the frame, coils can be made using a plastic box (cable channel) of a suitable cross-section. For example, for 80 - 100 turns of wire with a cross-section of 0.3...0.5 mm, a box with a cross-section of 15 X 10 or less is quite suitable, depending on the cross-section of your specific wire for winding. Single-core copper wire for low-current electrical circuits is suitable as a winding wire; it is sold in coils, such as CQR, KSPV, etc. This is bare copper wire with PVC insulation. The cable may contain 2 or more single-core wires with a cross-section of 0.3 ... 0.5 mm in insulation of different colors. We remove the outer sheath of the cable and get several necessary wires. Such a wire is convenient in that it eliminates the possibility of short-circuiting turns due to poor-quality insulation (as in the case of wires with varnish insulation of PEL or PEV brands, where minor damage is not visible to the eye). To determine how long the wire should be to wind the coil, you need to multiply the circumference of the coil by the number of its turns and leave a small margin for the terminals. If you do not have a piece of wire of the required length, you can wind it from several pieces of wire, the ends of which are well soldered to each other and carefully insulated with electrical tape or using heat-shrink tubing.
Remove the cover from the cable channel and cut the side walls with a sharp knife every 1 ... 2 cm:
After this, the cable channel can easily go around a cylindrical surface of the required diameter (jar, pan, etc.), corresponding to the diameter of the metal detector coil. The ends of the cable channel are glued together and a cylindrical frame with sides is obtained. It is not difficult to wind the required number of turns of wire onto such a frame and coat them, for example, with varnish, epoxy, or fill everything with sealant.
From above, the frame with the wire is closed with a cable channel cover. If the sides of this lid are not high (this depends on the size and type of box), then you don’t have to make side cuts on it, because it bends quite well anyway. The output ends of the coil are brought out next to each other.
This results in a sealed coil with good structural rigidity. All sharp edges, protrusions and irregularities in the cable channel should be smoothed using sandpaper or wrapped with a layer of electrical tape.
After checking the coil for functionality (this can be done by connecting the coil even without a screen to your metal detector for the presence of generation), filling it with glue or sealant and mechanically processing the irregularities, you should make a screen. To do this, take foil from electrolytic capacitors or food foil from the store, which is cut into strips 1.5 ... 2 cm wide. The foil is wound tightly around the coil, without gaps, overlapping. Between the ends of the foil in the place of the coil terminals you need to leave gap 1 ... 1.5 cm , otherwise a short-circuited turn will form and the coil will not work. The ends of the foil should be secured with glue. Then the top of the foil is wrapped along the entire length with any tinned wire (without insulation) in a spiral, in increments of about 1 cm. The wire must be tinned, otherwise incompatible metal contact (aluminum-copper) may occur. One end of this wire will be the coil's common wire (GND).
Then the entire coil is wrapped with two or three layers of electrical tape to protect the foil screen from mechanical damage.
Tuning the coil to the desired frequency involves selecting capacitors, which together with the coil form an oscillatory circuit:
The actual inductance of the coil, as a rule, does not correspond to its calculated value, so the desired circuit frequency can be achieved by selecting appropriate capacitors. To facilitate the selection of these capacitors, it is convenient to make a so-called “capacitor store”. To do this, you can take a suitable switch, for example, the P2K type with 5 ... 10 buttons (or several such switches with fewer buttons), with dependent or independent latching (all the same, the main thing is that it is possible to turn on several buttons at the same time). The more buttons there are on your switch, the correspondingly more containers can be included in the “store”. The diagram is simple and is shown below. The entire installation is hinged, the capacitors are soldered directly to the button terminals.
Here is an example for selecting capacitors series oscillating circuit
(two capacitors + coil) with capacities of about 5600 pF. By switching buttons, you can use different capacities indicated on the corresponding button. In addition, by turning on several buttons at the same time, you can get the total capacities. For example, if you press buttons 3 and 4 simultaneously, we get a total capacitance of 5610 pF (5100 + 510), and when you press 3 and 5 – 5950 pF (5100 + 850). In this way, you can create the necessary set of capacitors to accurately select the desired circuit tuning frequency. You need to select capacitor capacities in the “capacitance store” based on the values given in your metal detector circuit. In the example given here, the capacitances of the capacitors according to the diagram are indicated as 5600pF. Therefore, the first thing included in the “store” is, of course, these containers. Well, then take capacitances with lower ratings (4700, 4300, 3900 pF for example), and very small ones (100, 300, 470, 1000 pF) for a more accurate selection. Thus, by simply switching buttons and their combinations, you can obtain a very wide range of capacitances and tune the coil to the required frequency. Well, then all that remains is to select capacitors with a capacitance equal to what you got as a result at the “capacitance store”. Capacitors with such a capacity should be placed in the working circuit. It should be borne in mind that when selecting containers, the “magazine” itself must be connected to a metal detector exactly the wire/cable that will be used in the future, and the wires connecting the “magazine” to the coil must be made as short as possible! Because all wires also have their own capacity.
Discuss the article METAL DETECTORS: ABOUT COILS
For a gasoline internal combustion engine, the ignition system is one of the determining ones, although it is difficult to single out any main component in the car. You can’t go without a motor, but it’s also impossible without a wheel.
The ignition coil creates high voltage, without which it is impossible to form a spark and ignite the fuel-air mixture in the cylinders of a gasoline engine.
Briefly about ignition
To understand why there is a reel in a car (this is a popular name), and what part it takes in ensuring movement, you need to at least generally understand the structure of ignition systems.
A simplified diagram of how the reel works is shown below. 
The positive terminal of the coil is connected to the positive terminal of the battery, and with the other terminal it is connected to the voltage distributor. This connection scheme is classic and is widely used on VAZ family cars. To complete the picture, it is necessary to make a number of clarifications:
- The voltage distributor is a kind of dispatcher that supplies voltage to the cylinder in which the compression phase has occurred and the gasoline vapors should ignite.
- The operation of the ignition coil is controlled by a voltage switch; its design can be mechanical or electronic (contactless).
Mechanical devices were used in old cars: the VAZ 2106 and the like, but now they are almost completely replaced by electronic ones.
Reel design and operation
The modern bobbin is a simplified version of the Ruhmkorff induction coil. It was named after the German-born inventor Heinrich Ruhmkorff, who was the first to patent a device in 1851 that converts low-voltage direct voltage into high-alternating voltage.
To understand the principle of operation, you need to know the structure of the ignition coil and the basics of radio electronics. 
This is a traditional, common VAZ ignition coil, used for a long time and on many other cars. In fact, this is a pulse high-voltage transformer. On a core designed to enhance the magnetic field, a secondary winding is wound with a thin wire; it can contain up to thirty thousand turns of wire.
On top of the secondary winding is a primary winding made of thicker wire and with fewer turns (100-300).
The windings at one end are connected to each other, the second end of the primary is connected to the battery, the secondary winding with its free end is connected to the voltage distributor. The common point of the coil winding is connected to the voltage switch. This entire structure is covered by a protective housing.
A direct current flows through the “primary” in the initial state. When a spark needs to be formed, the circuit is broken by a switch or distributor. This leads to the formation of high voltage in the secondary winding. Voltage is supplied to the spark plug of the desired cylinder, where a spark is formed, causing combustion of the fuel mixture. High-voltage wires were used to connect the spark plugs to the distributor.
The single terminal design is not the only one possible; there are other options. 
- Double spark. The dual system is used for cylinders that operate in the same phase. Let's assume that compression occurs in the first cylinder and a spark is needed for ignition, and in the fourth cylinder there is a purge phase and an idle spark is formed there.
- Three-spark. The principle of operation is the same as that of a two-terminal one, only similar ones are used on 6-cylinder engines.
- Individual. Each spark plug is equipped with its own ignition coil. In this case, the windings are swapped - the primary is located under the secondary.
How to check the ignition coil
The main parameter by which the performance of the reel is determined is the resistance of the windings. There are average indicators that indicate its serviceability. Although deviations from the norm are not always an indicator of a malfunction.
Using a multimeter
Using a multimeter, you can check the ignition coil according to 3 parameters:
- primary winding resistance;
- secondary winding resistance;
- presence of a short circuit (insulation breakdown).
Please note that only an individual ignition coil can be checked in this way. Dual ones are designed differently, and you need to know the output circuit of the “primary” and “secondary”.
We check the primary winding by attaching probes to contacts B and K.
When measuring the “secondary” we connect one probe to contact B, and the second to the high-voltage terminal.
The insulation is measured through terminal B and the coil body. The device readings should be at least 50 MΩ.
It’s not always common for a car enthusiast to have a multimeter at hand and experience in using it; on a long journey, checking the ignition coil using this method is also not available.
other methods
Another method, especially relevant for old cars, including VAZs, is to check the spark. To do this, the central high-voltage wire is placed at a distance of 5-7 mm from the motor housing. If a blue or bright purple spark flashes when you try to start the car, the reel is working normally. If the color of the spark is lighter, yellow, or absent altogether, this may confirm that it is broken or the wire is faulty.
There is an easy way to test a system with individual coils. If the engine stalls, you just need to disconnect the power to the coils one by one while the engine is running. We disconnected the connector and the operating sound changed (the machine stalled) - the coil is fine. The sound remains the same - there is no spark to the spark plug in this cylinder.
True, the problem may also be in the spark plug itself, so for the purity of the experiment, you should swap the spark plug from this cylinder with any other.
Connecting the ignition coil
If during dismantling you did not remember and did not mark which wire went to which terminal, the ignition coil connection diagram is as follows. The terminal with the + sign or the letter B (battery) is supplied with power from the battery, and the switch is connected to the letter K. The colors of the wires in cars may vary, so it is easiest to track which goes where.
The correct connection is important, and if the polarity is incorrect, the bobbin itself, the distributor, or the switch can be damaged.
Conclusion
One of the important components in a car is the bobbin, which creates high voltage to produce a spark. If dips appear in the engine’s operation, it begins to stall and simply run unstably – this could be the cause. Therefore, it is important to know how to check the ignition coil correctly, and if necessary, using the old-fashioned method, in the field.
