What is hysteresis, what are the benefits and harms of this phenomenon
Definition of a concept
The word "Hysteresis" has Greek roots, it translates as lagging or lagging behind. This term is used in various fields of science and technology. In a general sense, the concept of hysteresis is distinguished by the different behavior of the system under opposite influences.
This can be said in simpler words. Suppose there is some kind of system that can be influenced in several directions. If, when acting on it in the forward direction, after termination, the system does not return to its original state, but is installed in an intermediate state, then in order to return to its original state, it is necessary to act in another 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 work at certain threshold values of the acting forces and for regulators. In other cases, hysteresis is detrimental, consider this in practice.
Hysteresis in Electrical Engineering
In electrical engineering, hysteresis is an important characteristic for the materials from which the cores of electrical machines and apparatuses are made. Before proceeding with the explanations, let's look at the core magnetization curve.
An image on a graph of this kind is also called a hysteresis loop.
Important! In this case, we are talking about the hysteresis of pheromagnets, here it is a nonlinear dependence of the internal magnetic induction of the material on the magnitude of the external magnetic induction, which depends on the previous state of the element.
When current flows through a conductor around the latter, a magnetic and electric field. If you wind the wire into a coil and pass current through it, you get an electromagnet. If you put a core inside the coil, then its inductance will increase, as well as the forces that arise around it.
Why does hysteresis depend? Accordingly, the core is made of metal, its characteristics and the magnetization curve depend on its type.
If you use, for example, hardened steel, then the hysteresis will be wider. When choosing the so-called soft magnetic materials - the schedule will be narrowed. What does this mean and what is it for?
The fact is that when such a coil operates in an alternating current circuit, current flows in one direction or another. As a result, and magnetic forces, the poles are constantly flipping.In a coreless coil, this happens in principle at the same time, but things are different with the core. It is gradually magnetized, its magnetic induction increases and gradually reaches an almost horizontal section of the graph, which is called the saturation section.
After that, if you start to change the direction of the current and the magnetic field, the core will need to be magnetized. But if you simply turn off the current and thereby remove the source of the magnetic field, the core will still remain magnetized, although not so much. In the following chart, this is point “A”. In order to demagnetize it to its initial state, it is necessary to create a negative magnetic field strength. This is point “B”. Accordingly, the current in the coil should flow in the opposite direction.
The value of the magnetic field strength for the complete demagnetization of the core is called the coercive force and the less it is, the better in this case.
The magnetization reversal in the opposite direction will take place similarly, but already along the lower branch of the loop. That is, when working in an AC circuit, part of the energy will be spent on magnetization reversal of the core. This leads to the fact that the efficiency of the electric motor and transformer is reduced. Accordingly, this leads to its heating.
Important! The smaller the hysteresis and coercive force, the smaller the loss of magnetization reversal of the core.
In addition to the above, hysteresis is also characteristic of the operation of relays and other electromagnetic switching devices. For example, trip and turn current. When the relay is off, for it to work, you need to apply a certain current. In this case, the current of its holding in the on state can be much lower than the switching current. It will turn off only when the current drops below the holding current.
Hysteresis in Electronics
In electronic devices, hysteresis carries mainly useful functions. Suppose this is used in threshold elements, for example, comparators and Schmidt triggers. Below you see a graph of its states:
This is necessary in cases where the device works when the signal X is reached, after which the signal can begin to decrease and the device does not turn off until the signal drops to level Y. This solution is used to suppress contact bounce, interference and random bursts, as well as in various controllers.
For example, a thermostat or a temperature controller. Usually its principle of action is to turn off the heating (or cooling) device at a time when the temperature in the room or other place has reached a predetermined level.
Consider two options for working briefly and simply:
- No hysteresis. Turn on and off at a given temperature. There are nuances here. If you set the temperature regulator to 22 degrees and heat the room to this level, then as soon as the room is 22 it will turn off, and when it drops back to 21 it will turn on. This is not always the right decision, because your controlled device will turn on and off too often. In addition, in most domestic and many production tasks there is no need for such a clear temperature support.
- With hysteresis. To make a certain gap in the allowable range of adjustable parameters, hysteresis is used. That is, if you set the temperature to 22 degrees, then as soon as it is reached, the heater will turn off. Suppose that the hysteresis in the controller is set to a gap of 3 degrees, then the heater will only work again when the air temperature drops to 19 degrees.
Sometimes this gap is adjusted at your discretion. In simple designs, bimetallic plates are used.
Finally, we recommend watching a useful video that tells you what hysteresis is and how you can use it:
We examined the phenomenon and application of hysteresis in electrics.The result is as follows: in an electric drive and transformers, it has a detrimental effect, and in electronics and various regulators, it also finds useful application. We hope the information provided was useful and interesting for you!
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