Induction Cooktop

Induction hob is the best assistant of the modern culinary specialist, basing the principle of action on the opening of the connection of electric current and magnetic induction. The purpose of the review is to show how the device works. The process is based on two physical phenomena: magnetization reversal and eddy currents.

. Place induction panels in the ranks of kitchen appliances.

The panel differs from a typical plate in the possibility of embedding. This is a flat design containing a certain number of burners. Obviously it is assumed that the owners have bought a tabletop or are ready to modify kitchen furniture. The hole of the desired shape is cut with an electric jigsaw, formed by a jointer, router, other tool. Usually around the perimeter of the panel shows a seal that allows the device to firmly sit on the designated place. Additional fasteners are often not required.

Embedded technology is good at saving space. It is known that only a small part of housewives use the oven. Therefore, it is not rational to spend space for storing dishes, and ordinary furniture looks more stylish than special cooking techniques. As for the price, the difference is transparent, much more attention should be paid to the sizes: the tabletops of the headsets show too little depth, and drawers are located below, which will prevent installation.

The forums decided to calculate how much gas is leaving to boil a kettle of water. The results were average. If the technical data of the tile said that the burner power is 1 kW, this did not coincide with the empirical results. The person created the topic, someone noticed that the efficiency is not taken into account in the calculations. Part of the heat evaporates, nothing can be done. Not to mention the infrared radiation of the kettle body into space.

gas stove efficiency is not able to rise above 50% with rare exceptions. Models have been created where exhaust air is started up in a special way to warm up the adjacent burners, but technologies that mimic the principle of operation of a condensing boiler are rather a wonder.90% of readers have not heard of this. It is difficult to find equipment for sale. The price is silent.

Electric tiles are more advanced, develop high rates, but induction carries true service. It is used to melt metals, on YouTube you will see a roller, where a hot, shapeless ball of hardened steel hangs in a magnetic alternating magnetic field: Foucault's currents do their work. Not surprisingly, magnetic induction heats pots and pans easily.

Not only high efficiency pleases the owners of induction cooking panels. Devices have a high degree of security. Ceramic or glass table cools quickly - you just remove the pan. A variable field has no visible effect on human flesh and skin. If the induction hob works by chance, leaning on the table is difficult to get burned.

The heating power is regulated by the frequency of change of the magnetic field of the working coil. Although complex algorithms are not excluded, when the current flows in bursts of pulses, and the degree of heat release changes by controlling the porosity of the packages. To do this, inside the induction panel there is an inverter that forms the desired frequency. The range, as a rule, is indicated in the technical specifications, although not every manufacturer is able to attend to this.

An important role is played by additional options. Often, when evaluating the superposition of fields, devices are able to automatically turn off after a time if the burners are inactive. There is a known case when a kitchen cleaning robot drove from a worktop onto an induction cooker and was damaged as a result, incompatible with life. During the trial, the manufacturer tried to prove that the suicide was planned by the owners: they left the device on purpose. If the induction hob had been turned off automatically, such an excess would have been impossible.

Eddy currents

In scientific literature, it is believed that eddy currents were discovered in 1820, when Oersted showed that electricity can move a magnetic needle. The difficulty of working with the object of the narration did not boil down to the fact that the first galvanometer was invented several years later: it is impossible to estimate the amplitude of the phenomenon using simple measuring instruments. The first eddy currents, apparently, were received in 1824 by Arago, who noticed that the magnetic needle responds to a copper disc rotating nearby: the alternating field created leads in the conductor, forming its own force field.

Our discussion subject is proudly named Foucault. This is a student of Arago, who was trying to penetrate the mystery of the arrow with an inquisitive mind. He first noticed that the conductor in addition heats up under the action of an alternating magnetic field. The clue was given by his own theory in 1931 by Faraday. He explained the phenomenon of induction of alternating currents, he already knew how two different matters are connected. Readers have already guessed that today the phenomenon is used in induction cooking panels. Eddy currents are formed in ferromagnetic metals and alloys under the influence of changes in the magnetic field. Their use in technology is widespread:

1. Asynchronous motors by and large operate at the expense of currents induced in the rotor. A silumin drum is riddled with squirrel cage shaped copper conductors, leading in such a way that the resulting emf will develop. While there is a difference between the speed of rotation of the field and the engine speed, the system tends to equilibrium. Equality is not achieved in normal operation.
   

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2. Panel Design. Electromagnetic braking is used to quickly stop the engine. In this case, the rotor rotates in the normal direction, the magnetic field in the opposite direction. Which quickly leads to the desired result. As is known, eddy currents are induced in the rotor, interacting with the field.
3. The induction transfer of metal melts acts in a similar way. The eddy currents create a field, the pump grabs them. In flat-linear inductors there are no moving parts, the performance is easily adjustable. Foundries use techniques for working with non-ferrous metals.
4. High frequency currents flow predominantly along the surface of the conductor. As a result, the density reaches high values. This phenomenon is used for surface hardening of metals when a part should not become brittle with external hardness: gear teeth, shaft journals, etc.
5. In 1980, Bose engineers invented an electromagnetic suspension. Those that use eddy currents, rather, are designed for thin systems. For example, gyro motors.
6. Nicola Tesla is rightly considered the father of the direction in medicine - diathermy. Passing high-frequency currents through his body, the scientist showed their harmlessness. Nicola even considered the impact beneficial. For example, for the skin. Today, high frequencies heat the organs.
7. The field of eddy currents is actively used for exploration of ore deposits. The field of high frequency is studied in order to assess the usefulness and prospects of development. Similar methods are used to identify the occurrence of reinforcement in the walls.
8. Based on the evaluation of the field of eddy currents based flaw detection wire, pipes, metal profile. At the same time, the structure of the stress vectors allows us to correctly withstand the geometric dimensions of the products.

Eddy currents are not always useful. In the cores of transformers, they cause significant losses, which simultaneously lead to heating of the equipment. To enhance the field, the wire is wound on ferromagnetic alloys, in order to reduce the effect, up to 4% silicon is added to electrical steel. This greatly increases the resistivity of the material. At the same time, the core is cut into thin plates( along the lines of tension) and insulated from each other with a layer of varnish, performing the blending.

It is easy to guess now why the dishes for the induction cooking panel are made of ferromagnetic alloys. The magnetic permeability of the material becomes a link between the field strength and induction formed in the bulk of the metal. Ferromagnetic alloy becomes an amplifier effect of eddy currents. The induction increases, the rate of its change increases, which directly increases the EMF in the metal. It is easy to see if you put an aluminum pan on the induction panel: the heating will slow down dramatically. Eddy currents affect the process and the magnetization reversal factor.

Remagnetization of metals

The name of the family of ferromagnets laid their key property. Other metals do not have this quality. It is about the ability to be magnetized. In transformers and electric motors, heat losses are considered parasitic. We have to use ferromagnets, which are considered to be conductors of an alternating field, but by all means trying to get rid of heat.

As for induction cooking panels, the opposite is true here. Scientists have long discovered that heat losses are estimated from the sample’s magnetic hysteresis curves. The initial curve of induction versus field strength has the shape of an integral slightly inclined to the right. These two physical quantities are related through the magnetic permeability of the material, but the nature of the graph is not linear. When the field strength decreases and its direction changes, the curve follows a different path. Acquires an integral form, but differs. It turns out a figure like a stadium with sharp teeth at the starting and ending point. This is called hysteresis: a different path of the process in the forward and reverse direction.

The initial curve( during the first pass) allows you to determine the dependence of the magnetic permeability of the material on the field strength. Heat losses are characterized by the area of ​​the hysteresis loop. It is found by integration or is considered manually, having previously depicted a graph on graph paper( estimate of the number of cells inside the figure).A thick ferromagnetic alloy disc is placed on the bottom of a cooker specifically designed to be used in pairs with an induction hob.

The more often the field changes direction, the higher the loss in the hysteresis loop. But if the frequency dependence is linear, the eddy currents are determined by its square. This imposes specificity. At high frequencies, the eddy currents cause the lion's share of heating. But! With increasing frequency, the field begins to radiate actively into the surrounding space, which is unacceptable. Therefore, the manufacturer finds a middle ground and tries to use the effect of magnetization reversal to the maximum. To assess the magnitude of heat losses in laboratory work, the schedule is built on an oscilloscope, removed manually for further research.

Important. In connection with the above, be aware that it is dangerous for people with a pacemaker to use an induction cooker: kitchen appliances can adversely affect the operation of a life-support device.