Various physical, chemical, economic and even social phenomena are characterized by a reaction delay effect. This phenomenon occurs as a result of a reaction to a certain irritation, action or influence. The article will give a detailed description of what hysteresis is. Describes its most common variants, the influence of this effect in electrical engineering and electronics.
A loop
To calculate this phenomenon and its influence on a specific system or object, a hysteresis loop is used. It is a graph on which the curve of the initial state of the system and the course of its response to excitation is superimposed.
The effect of hysteresis can be different: it can have both beneficial and negative properties. This phenomenon is taken into account in various fields: it can be physics, economics and even sociology. In physics, hysteresis is necessarily taken into account when calculating various quantities, the interaction of forces, powers and magnetic fields. The most common types of hysteresis are:
- Magnetic.
- Elastic.
- Ferroelectric.
Each type of this phenomenon will be described in more detail below.
Elastic
The phenomenon of elastic hysteresis is characteristic of various metals. This can be explained in clear language like this.
A metal rod rests on a support at one end. The metal is currently in a calm state, and at the same time has its own deformation elasticity. We apply a certain pressure to the free end of the rod, for example, using a press. In the metal, under the influence of increasing pressure, the following properties will begin to appear:
- Primary increase in elastic force.
- A jump in elasticity to maximum values.
- Reduction of counterforce as a result of exceeding the maximum elastic characteristics.
If you continue to increase the pressure, it can bend, break or crumble the rod. If you interrupt the process of influencing the rod, this will lead to the following:
- To a jump in dynamic stress on the rod in the direction of decreasing pressure.
- General load reduction.
After the load is removed, the rod will return to its original characteristics. Depending on the type of metal, the characteristics may return completely or partially. If the metal is viscoelastic, its hysteresis loop will have a narrow structure due to the incomplete return of the metal to its original state
Elastic hysteresis can be of two types:
- Static type. Characteristic of viscoelastic or inelastic deformation. Such deformation is not able to completely restore elasticity parameters and stress upon complete or partial removal of loads. For example, a rod bends under load and cannot restore its condition after the end of the impact.
- Dynamic type. With such hysteresis, the load on the system is not able to reach the limit of its elasticity characteristic, even if the impact is cyclical. The reasons for this type of hysteresis can be different, for example, it can be forces of magnetic or thermal elasticity.
- Elastic hysteresis is highly dependent on the composition of the starting material and the ability of microparticles to change their dislocation when pressure or load changes.
Magnetic
A frequently occurring hysteresis in electrical engineering is magnetic. In this area, elements with magnetization/demagnetization properties are used. Various transformers and inductors have ferromagnetic cores, the material of which determines the strength of the magnetic field of the element. To study the influence of core materials with different properties, ferromagnetic hysteresis loops are used. Also, using a loop, you can study the nonlinear dependence of internal magnetic inductions on the external magnetic field.
When alternating current flows through the coil, a magnetization lag effect occurs. This is due to the fact that after opening the circuit (de-energizing), the ferromagnetic core does not demagnetize completely, but retains part of the magnetization with the pole orientation.
To change the polarity of the core, it will need to be re-magnetized. This will require changing the direction of the current, overcoming the coercive force and spending a little more energy. Overcoming the coercive force and increasing energy will lead to heating of the core. All these forces and costs lead to the effect of hysteresis losses. For such ferromagnets, the hysteresis loop will be wider.
Ferromagnetic materials are distinguished by their ability to quickly change residual magnetization:
- Magnetic soft. Such cores can be found in transformers and inductors. They are characterized by a narrower hysteresis loop.
- Magnetically hard. Used for memory elements or magnets. They are characterized by a wide loop in the graph, a large loss of hysteresis and heating during magnetization reversal.
The magnetization of cores is expressed not only in their ability to maintain a magnetic field with a certain pole. Such elements are also influenced by the direction of rotation of the fields, which lead to shifts in the timing characteristics of magnetization.
Magnetic hysteresis is also characterized by the presence of a double loop. This effect is entirely dependent on the ability to retain residual magnetism. The first outer loop denotes the maximum hysteresis, and the inner loop is the frequency cycle loop.
The properties of magnetic hysteresis are used in electrical engineering to create electric motors, switching equipment, and various magnetic relays.
Ferroelectric
Dielectric materials have no free charges. Their electrons are tied to atoms and are unable to move. When a dielectric is exposed to a strong magnetic field, its charges become polarized and change orientation to the opposite. The higher the field, the higher the polarization vector. It grows non-linearly. A dielectric has a polarization threshold, upon reaching which dielectric or ferroelectric hysteresis occurs.
The amount of polarization is often affected by an increase in the temperature of the dielectric. When a certain temperature is reached (depending on the properties of the material), spontaneous and uncontrolled polarization begins, which does not depend on external electric fields.
Electric
In electronics, a concept called electrical hysteresis is used. For this area, this phenomenon has both beneficial and harmful properties.
Definition of the concept
The word “Hysteresis” has Greek roots and is translated as lagging or lagging. This term is used in various fields of science and technology. In a general sense, the concept of hysteresis distinguishes the different behavior of a system under opposite influences.
This can be said in simpler words. Let's say there is some kind of system that can be influenced in several directions. If, when acting on it in the direct direction, after stopping the system does not return to its original state, but is established in an intermediate state, then in order to return it to its original state, it is necessary to act in a different direction with some force. In this case, the system has hysteresis.
Sometimes this phenomenon is used for useful purposes, for example, to create elements that operate at certain threshold values of acting forces and for regulators. In other cases, hysteresis has a detrimental effect; let’s consider this in practice.
Useful hysteresis
Hysteresis in electronics is used to create electronic thermostats. Such devices operate on the principle of turning on or off when a certain condition is reached. For example, if the difference is set to 2 degrees, and the temperature setting is 20 degrees, then the thermostat will turn on when it reaches 18 degrees, and turn off when the temperature reaches 22 degrees. This approach helps to significantly reduce electrical energy consumption when the heater is constantly operating.
This effect is also used when triggers operate. Hysteresis helps ensure precise switching without the influence of interference, voltage surges or magnetic fields.
This phenomenon can occur on bimetallic plates. Such elements are capable of losing and regaining the elasticity of their structure when temperature changes. When the material is heated, thermal expansion occurs, which changes the mechanical stress of the entire structure. As a result, the contact opens. After cooling, the plate structure takes on its original size, returns its original mechanical stress and closes the contact. Such thermostats are often installed in heating appliances (stoves, irons, kettles). The moment between heating and cooling is called the temperature gap. It is established only depending on the ability of a substance to expand and contract at a certain temperature.
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.
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.
Magnetizing energy
The loop is considered asymmetrical in the case when the maxima of the H1 field, which are applied in the reverse and forward directions, are not the same. Above we described a loop that is characteristic of a slow process of magnetization reversal. With them, quasi-equilibrium relationships between the values of H and M are maintained. It is necessary to pay attention to the fact that during magnetization or demagnetization, M lags behind H. And this leads to the fact that all the energy that is acquired by the ferromagnetic material during magnetization is not given up completely when going through the demagnetization cycle. And this difference all goes into heating the ferromagnet. And the magnetic hysteresis loop turns out to be asymmetrical in this case.
DIY refrigerator thermostat repair (video)
A temperature controlled thermostat is a simple device that allows you to automate the operation of heating, heating and air conditioning equipment. Thanks to the thermostat, electrical appliances can be automatically used for their actual purpose, reducing energy consumption. The recommendations presented above will help you choose a thermostat. And if you can’t find the most suitable device, you can always assemble the thermostat yourself!
How to make a thermostat for an incubator with your own hands
An incubator is an indispensable thing in agriculture, which allows you to hatch chicks at home. The incubator temperature can be controlled using a thermostat. A thermal relay for an incubator can be purchased, or you can assemble it yourself from scrap materials.
There are two ways to make a thermostat for an incubator:
- Using a zener diode, a thyristor and 4 diodes with a power of at least 700 W. The temperature control is carried out through a variable resistor with a resistance in the range from 30 to 50 kOhm. The temperature sensor in this device is a transistor installed in a glass tube and placed on a tray with eggs.
- Using a thermostat. You will need to attach a screw to the thermostat body using a soldering iron and connect it to the contacts. Rotating the screw will adjust the temperature.
The second method is considered the simplest and most accessible. Regardless of the type of thermostat, before laying eggs, the incubator must be warmed up and a homemade thermostat must be adjusted.
Single-domain ferromagnets
If the particles have different sizes, a rotation process occurs. This happens due to the fact that the formation of new domains is unfavorable from an energy point of view. But the process of particle rotation is hampered by anisotropy (magnetic). It can have different origins - form in the crystal itself, arise as a result of elastic stress, etc.). But it is precisely with the help of this anisotropy that the magnetization is retained by the internal field. It is also called the effective magnetic anisotropy field. And magnetic hysteresis occurs due to the fact that magnetization changes in two directions - forward and reverse. During the magnetization reversal of single-domain ferromagnets, several jumps occur. The magnetization vector M turns towards the field H. Moreover, the rotation can be uniform or inhomogeneous.
Hysteresis losses
During dynamic magnetization reversal of a ferromagnet by an alternating magnetic field, losses are observed. Moreover, they constitute only a small fraction of the total magnetic losses. If the loops have the same height (the same maximum magnetization value M), the dynamic type loop turns out to be wider than the static one. This happens due to the fact that new ones are added to all losses. These are dynamic losses, they are usually associated with eddy current and magnetic viscosity. In total, quite significant losses due to hysteresis are obtained.
Multi-domain ferromagnets
In them, the magnetization curve is constructed in a similar way, but the processes occur differently. When magnetization reversal occurs, domain boundaries shift. Consequently, one of the reasons for the occurrence of hysteresis may be a delay in boundary displacements, as well as irreversible jumps. Sometimes (if ferromagnets have a fairly large field) magnetic hysteresis is determined by a delay in the growth and formation of magnetization reversal nuclei. It is from these nuclei that the domain structure of ferromagnetic substances is formed.
