What is hysteresis, what are the benefits and harms of this phenomenon?

To denote retarded processes, a special name is used: hysteresis; what it is in electrical engineering can be understood after studying the information presented below. The general definition implies the presence of a certain delay to external influence. Changing the system depends on its previous state. This phenomenon differs from inertia in the nonlinearity of operating characteristics.

The hysteresis loop demonstrates the change in magnetization of a sample made of ferromagnetic material

General concepts of hysteresis

The following practical examples illustrate the basic definitions of the process. What is hysteresis in economics? When considering this area of ​​activity, you can study the standard organization of export of goods. To develop a new territory, you need to perform several actions:

• explore potential interest in certain products through market research;
• check for competitive offers;
• create a dealer network (sales and technical service);
• provide primary supply;
• conduct an advertising campaign.

At the initial stage, you will have to make quite a lot of effort. Further, a well-established trading mechanism will bring profit in operating mode. At this stage, less expensive control functions become more important. If the business needs to be moved to another region, the process is repeated in a similar way with a certain time delay. The above graph clearly demonstrates the change in economic parameters using the example of physical quantities.

Substances and their magnetic properties

Samples made from different materials react in a special way to the influence of a magnetic field. The main differences are determined by magnetic permeability (μ). This is a coefficient (multiplier) showing the difference in the vector value of induction ( B ) in this substance compared to vacuum ( B0 ) :

• diamagnetic materials (μ≤1) – copper, water, hydrogen;
• paramegnetics (μ≥1) – ebonite, oxygen, platinum;
• ferromagnets (μ significantly greater than 1) - cobalt, nickel, iron.

Magnetic core

The last group is distinguished by magnetism, which remains after removal of external influences.

For your information. When a ferromagnet is heated to a certain level (Curie point), the magnetic properties disappear. For iron this figure is +770°C.

Magnetization (M) can be defined as the difference between inductions (B-B0), or expressed through permeability by the following formula:

M = μ* B0 - B0 = (μ-1)*B0.

Varieties

Modern heating devices can be equipped with an adjustable or fixed temperature controller. The cyclic switching behavior of the element depends on this characteristic.

1. Fixed. These regulators already have preset closing/opening settings, with a fixed hysteresis. The advantage of such an element is that there is no need to independently set the trigger moment.

2. Adjustable. The most common. They are of the electromechanical type. The adjustment is made by increasing or decreasing the mechanical pressure on the bimetallic plate. Adjustment is made by rotating the screw. The greater the pressure on the plate, the higher the response threshold during heating. Such devices are cheaper than fixed ones and are more dependent on the state of the power circuit contact.

When purchasing a heating device, it is important to know about the cyclical nature of its operation. This will help you set up and maintain the required mode.

Types of hysteresis in physics

What is the source of the magnetic field

To solve practical electrical problems, magnetic hysteresis should be studied in detail. A complete understanding of similar phenomena based on physical principles can be obtained after considering ferroelectric and elastic processes.

Magnetic hysteresis

According to the basic definition, this phenomenon refers to the lag of the magnetization (M) of a material from the changing influence of an external field. For the experiment, you can assemble a circuit in which current is passed through a solenoid. The voltage level (H) is adjusted using a parallel variable resistor. The core is made of ferromagnet.

Experimental setup diagram

Important! The presented dependencies should be considered in conjunction with the graph in the first figure.

Before the experiment begins, the sample has neutral characteristics. Magnetization and intensity are zero, the magnetic moments of the domains are randomly located. After closing the circuit and increasing the current, the voltage increases. The figure shows how at the same time the direction of the moments changes. The induction in the sample ( B ) is equal to the sum of the voltage and magnetization with a correction factor (μ0):

B = μ0*H + μ0*M.

At a certain level, the μ0*M indicator increases to a maximum value. A subsequent change in the external field strength does not have any effect on it.

Ferroelectric hysteresis

The reason for the special shape of the graph in this example is the formation of polarization without the application of external field forces. This effect is observed in a certain temperature range. The corresponding materials are called ferroelectrics.

Ferroelectrics

The first figure shows the hysteresis loop, where the places are marked:

• point “a” – saturation state;
• Pc – residual polarization;
• -Ec – coercive force.

The second part (2) shows the chaotic (a) and directional (b) arrangement of domains. Orientation along electrostatic field lines is used to create capacitors with variable capacitance.

For your information. As in other substances, when the temperature rises to the level of the Curie point, magnetization disappears.

Elastic hysteresis

This phenomenon is explained by the special mechanical properties of individual materials. They retain the shape created by a fairly strong impact. A typical example is the manufacture of metal products using forging.

Magnetization or BH curve

The set of magnetization curves above provides an example of the relationship between B and H for soft iron and steel cores, but each type of core material will have its own set of magnetic hysteresis curves. You may notice that the flux density increases in proportion to the field strength until it reaches a certain value where it can no longer become nearly equal and constant as the field strength continues to increase.

This is because there is a limit to the amount of flux density that can be generated by the core since all the domains in the iron are perfectly aligned. Any further increase will not affect the value of M, and the point on the graph where the flux density reaches its limit is called magnetic saturation, also known as core saturation, and in our simple example above the saturation point of the steel curve begins at about 3000 ampere turns at meter.

Saturation occurs because, as we remember from the previous article on magnetism, which included Weber's theory, the random arrangement of the molecular structure in the core material changes when the tiny molecular magnets in the material become "aligned."

As the magnetic field strength (H) increases, these molecular magnets become more and more aligned until they reach perfect alignment, producing maximum flux density, and any increase in magnetic field strength due to increased electric current flowing through the coil will have will have little or no effect.

The mechanism of occurrence of the hysteresis loop

Hall effect

To study this process in detail, it is necessary to analyze individual sections of the curve indicating the change in induction. Description of the main stages:

1. first, a shift in the boundaries between neighboring domains is observed;
2. then the orientation of the moments changes quickly in the direction of the external field lines;
3. at this stage, the new location of the boundaries becomes irreversible;
4. this area is characterized by the growth of individual domains to a maximum size, the magnetic moments are located in exact accordance with the lines of the influencing field;
5. the final section shows the absence of influence on the magnetic moments of the tension created by the solenoid.

If you reduce the force parameters of the external field, a hysteresis loop is formed, which can be shown in the first picture (in the direction of the arrows). Please note that the curves are different. The induction delay corresponds to the basic principles of the phenomenon. At zero voltage B≠0. This quantity is called residual induction. This feature explains the understandable process of creating a permanent magnet. The core retains appropriate properties even after the power source is turned off.

Magnetization can be removed by raising the temperature to the Curie point of a particular material. A similar result is obtained using an appropriate external force field (-Hc). This tension creates a coercive force sufficient to demagnetize a steel or other ferromagnetic core. A completely completed cycle is called a magnetic hysteresis loop.

Application of hysteresis in electrical engineering and electronics

The magnetization of materials and the characteristics of transient processes should be taken into account when creating motors and transformers. When operating this equipment in alternating current circuits, part of the electricity consumed must be used to remagnetize the installed core. Similar phenomena are observed during the operation of switching devices. The study of hysteresis helps increase the efficiency of power machines and voltage converters and ensure the required relay switching speed.

Schmidt trigger

The figure shows the transfer characteristic of a Schmidt trigger. Changing the output signal with a certain delay is used to eliminate errors in the transmission of information. A conventional inverter responds to impulse noise by immediately switching. In this case, the time delay serves as a useful filter. It helps to correctly perceive control signals in difficult operating conditions.

Such solutions are used in electronics to eliminate problems with contact bounce. The calculated slowdown in operating reactions can be explained using a typical thermostat. If such a device is designed without hysteresis, switching will occur too often. However, in real conditions (room heating), an accuracy of ±3°C is quite sufficient. By increasing the width of the loop, you can set the optimal range to maintain a given temperature.

Error

In electronics, hysteresis can also harm the operation of some devices. This effect is called hysteresis error. Often this effect can be observed with a motion sensor. For example, when an object moves from point A to point B, the sensor is triggered within 1 second. And when moving in the opposite direction while maintaining the trajectory, the sensor turns on with a slowdown of 2 seconds. The reason for this phenomenon lies in the difference in output signals for input signals, which differ in magnitude when decreasing and increasing. When moving from point A to point B, the value of the incoming signal has a difference of 30 MB from the value of the same signal when moving in the opposite direction. Taking into account the sensor sensitivity of 15 MB/mm, the hysteresis will be 3 mm. The difference in signal magnitude depends on changes in air temperature, external interference, the effect of friction or contact bounce.

Using a graphical representation of hysteresis for calculations

For a visual experiment, you can assemble a simple diagram presented below:

• resistor R1 limits the alternating current passing through the coil winding;
• the voltage is removed from element R2 to form a picture on the oscilloscope screen;
• The capacitance of the capacitor is selected in such a way that 1/(w*C) is much less than R3.

Experiment

After connecting to an oscilloscope, you can observe the hysteresis loop on the screen. This real-scale image can be used to calculate and evaluate the performance of the created coil. The following list shows the correspondence of individual segments to the parameters discussed above:

• OA – coercive force;
• OS – residual induction;
• OD – saturation induction;
• OB – magnetic field.

For your information. Based on the established loop area, losses can be determined. The size of this area corresponds to the work that is spent on compensating the coercive forces. This energy heats up the ferromagnet and is actually wasted.

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Saturday, September 27, 2014 12:07 + in quotation book
Fragment from Alexandra Marinina’s book “Death for the sake of death” (1995) “... Once upon a time there lived in the city of Moscow a talented physicist Grigory Voitovich.
He did not marry for a very long time, he kept choosing a wife for himself, and finally chose the young dazzling beauty Evgenia. Look, here is a photograph of her from the period when she met Voitovich. They got married and had a daughter. All the men were jealous of little bald Grisha Voitovich, who managed to “snatch” such a tidbit for himself. Evgenia loved her husband and remained faithful to him; peace and tranquility reigned in the family. Several months ago, while working on a planned topic, Voitovich noticed that the device they were developing had the so-called opposite effect. The experimental animals reacted to it very aggressively, even to the point of devouring each other, which is generally not typical for them. Since the device was intended for use in an urban environment, Grigory Ilyich began to insist on presenting the results of observations of experimental animals in the final report on the topic. This would undoubtedly lead to the disclosure of the fact that the antenna, which has a completely peaceful purpose, also produces the opposite effect, which is expressed in a sharp increase in the aggressiveness of living beings within the field of action of the reverse loop. But some people really didn’t like this idea. This someone began to dissuade Voitovich from conscientiously presenting the results of the experiment. I don’t know how he persuaded him, what he used to get him, it’s possible that it was money, but he achieved his goal. The report was falsified; there was not a single word in it that in the direct action field of the antenna there was a side effect of a decrease in aggressiveness, but in the reverse action field the aggressiveness sharply increased. The antenna developers hid this data. For what? This is what I would like to know. Having received the answer to this question, I would answer all the others. Do you, Vadim, happen to know why they hid the data and falsified the report? No? It's a pity, I had so much hope for you. Okay, I'll continue. Grigory Ilyich Voitovich with his beautiful wife and charming baby daughter live not far from the Institute, right on the territory covered by that same “reverse loop”. And after some time, Voitovich begins to feel the effect of the antenna on his own skin. The beauty and youth of his wife, which had previously been a source of pride and adoration for him, suddenly turned into a constant source of jealousy. The jealousy deepened and deepened, quarrels in the family, which had never existed before, became almost daily and more and more violent, with shouting, breaking dishes and threats. Voitovich worked a lot, stayed at the Institute until late, sat there on weekends and holidays, and practically never went anywhere except home and his laboratory. In other words, for several months he was under the continuous influence of the antenna. He could not help but understand what was happening to him, and several times he turned to the person with whom he had once worked on the antenna and asked him to make public the true results of the experiments. And again this man managed to persuade Voitovich. How? How? I don't know, but I really want to find out. Finally, the worst thing happens - Voitovich kills his beloved wife. The antenna affects people differently, depending on the duration of stay in the field of influence and on the individual characteristics of the nervous system and psyche. Voitovich was unlucky, his psyche responded to the influence of the reverse effect very violently, and he was in the field of influence almost constantly for six months. He didn’t even understand that he had killed his wife, he couldn’t believe it, when the police arrived he was half mad. He was picked up and taken to the place of preliminary detention, quite far from the Institute and from the antenna. And he began to come to his senses. He began to realize what had happened, to remember how and why he committed the murder. And I realized that it was all my fault. He allowed himself to be persuaded, showed weakness, gave in to temptation... You don’t know, Vadim, to what temptation he gave in? No? It's a pity. So, Voitovich understands that he alone is to blame for everything. You ask him to be allowed to go home. Three days later, he commits suicide, writing a suicide note with the following words: “The roots of our guilt go to infinity.” Do you understand the meaning of this phrase, Vadim? Not again? Well, I'll explain it to you now. Look at this for starters. Open the folder and look. Open up, open up, don't be shy. These are photographs of the brutally stabbed Evgenia Voitovich. And these are victims of other crimes committed on the territory of that same “reverse loop”. This boy was beaten to death by schoolchildren, eighth grade students. Do you know why? He was walking his dog near the ground where they were playing football. The dog saw the ball, snatched the leash from his hands and ran out onto the playground. She was young and not yet trained, she really wanted to play. The young football players were very unhappy that there was a dog on the field, and they killed the owner, who was eight years old. Look what they turned it into. Look, Vadim, look carefully, it will be useful to you. And these are two girls, sixth grade students, they are eleven years old. They were raped and killed by vocational school students, fourteen boys aged sixteen to seventeen. But this man happened to be there by chance, he was one of the guests, he wanted to light a cigarette on the street, but he had no matches, and, to his misfortune, he asked for a light from a group of young people who were discussing something in the park. It seemed to them that the passerby was not polite enough when he told them: “Guys, won’t you have a light?” They felt he should have said hello first. They couldn’t identify him for a long time because he didn’t take documents with him when visiting, and the young people turned his face into a shapeless mess. And this is a paralyzed old woman who was killed by her own daughter. The old woman was completely immobilized, but her speech was preserved, and she, like every sick person, and an elderly one at that, was unbearable. She was capricious, nagging, complaining, and did not give her daughter the opportunity to lead at least some kind of personal life. But is this why they kill? And so cruel too. Look, Vadim, carefully, this is all I could collect, but I had little time. This is only a small part of the nightmare that took place in the Eastern District of our city. But this is enough to understand what the price was paid for the fact that someone managed to persuade Voitovich to remain silent. So, maybe you can tell me why he was silent? Why did he force people to pay such a monstrous price? Not again? Okay, give me a folder with photos here, now look at this map. This is the Eastern District, this is where the Institute is located. Do you see the wrong eight? The larger loop coincides with the field of direct action of the antenna and, accordingly, the field of the side effect in the form of a decrease in aggressiveness. There are very few dots here, and these dots indicate the places where murders and rapes took place. And even those dots that exist are of different colors, but among them there are almost no black or purple ones. This means that murders here, of course, are committed, but predominantly not for hooligan or domestic reasons, not in the family, but for self-interest, revenge, on order, in order to conceal another crime, for example, rape. In general, there are much fewer murders here than in any other area of ​​the city. But the loop, which is smaller, almost entirely consists of purple and black dots; they indicate domestic and hooligan murders. Do you know what murder for hooligan reasons is? This is when they kill a person with whom there is no relationship, with whom nothing connects, they kill just like that, because they didn’t like the color of his hair, or because he asked for a light without first saying “Good evening, citizens,” or just because you're in a bad mood and you want to kill someone. Why are you looking at me like that, Vadim? Don't you know that people are killed because of this? Well, yes, of course, you have state interests, what do you care about our everyday police worries, you don’t even know why ordinary people kill other ordinary people, you have only spy passions on your mind ... "(p. 20 ) Read the book [/td]

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Marinina Alexandra Marina Alexandrova novel quotes books antenna aggressiveness detectives crime scientific developments research

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Magnetic hysteresis area

Materials with magnetic properties are divided into two groups according to the width of the hysteresis loop. Soft magnetic ones (narrow diagram) are distinguished by a relatively low coercive force and corresponding lower energy costs. Such products are used for the manufacture of electric motors, drives, and voltage transformers.

Soft and hard magnetic materials

Hard magnetic materials are characterized by an increased response time to exposure to an external field. These materials are used to create memory chips and permanent magnets.