An electromagnetic coil is an electrical conductor such as a wire in the form of a coil, spiral or helix. Electromagnetic coils are used in electrical engineering, in applications where electric current interacts with magnetic fields, in devices such as electric motors, generators, inductors, electromagnets, transformers, and sensor windings. Either an electric current is passed through the coil wire to produce a magnetic field, or otherwise an external time-varying magnetic field through the inside of the coil produces EMF (voltage) across the conductor.
The current through the conductor creates a circular magnetic field around the conductor because of Ampere's law. The advantage of using a coil shape is that it increases the strength of the magnetic field generated by the given current. The magnetic fields generated by the separate wire windings all pass through the center of the coil and add (superpose) to produce a strong field there. The more wire turns, the stronger the field will be. In contrast, external magnetic flux transforms induces voltage in a conductor such as a wire, because of Faraday's induction law. The induced voltage can be increased by rolling the wire into a coil, because the field lines cut the circuit several times.
The direction of the magnetic field generated by the coil can be determined by the right hand grip rule. If the radius of the right hand wraps around the magnetic core of the coil toward the conventional current through the wire, the thumb will point toward the magnetic field line through the coil. The tip of the magnetic core from which the field lines appear is defined as the North pole.
There are many types of coils used in electrical and electronic equipment.
Video Electromagnetic coil
Rolls and taps
The wire or conductor which is a coil is called winding . The hole in the center of the coil is called the core or the magnetic axis area. Each loop of wire is called play . In rolls where the bends are in contact, the wire must be insulated with a non-conductive insulating layer such as a plastic or enamel to prevent the current passing between the wires to change. Winding is often wrapped around a coil shape made of plastic or other material to hold it in place. The wire end is taken out and paired to an external circuit. The roll may have an additional electrical connection along its length; this is called tapping . The winding that has one tap in the middle of its length is called centered .
Coils can have more than one reel, electrically isolated from each other. When there are two or more windings around the general magnetic axis, the coil is said to be inductively combined or magnetically coupled . The time flow varies through a single winding will create a magnetic field that varies the time that passes through the other windings, which will induce time voltages varying in the other coils. This is called a transformer. The currently applied winding, which creates a magnetic field, is called the primary winding . The other scrolls are called secondary scrolls .
Maps Electromagnetic coil
Magnetic core
Many electromagnetic coils have a magnetic core, a piece of ferromagnetic material such as iron in the middle to increase the magnetic field. The current through the coil memagnitasi iron, and the field of magnetic material to increase the field generated by the wire. This is called ferromagnetic-core or iron-core coil . The ferromagnetic core can increase the magnetic field and the inductance of the coils as many as hundreds or thousands of times beyond what would happen without a nucleus. A ferrite coil core is a variety of coils with a core made of ferrite, a ferrimagnetic ceramic compound. The ferrite coil has a lower core loss at high frequencies.
- A coil with a core that forms a closed loop, perhaps with some narrow air gap, is called a closed-core coil. By providing a closed path for magnetic field lines, this geometry minimizes the magnetic reluctance and produces the strongest magnetic field. It is often used in transformers.
- The general form for closed core windings is the toroidal coil , where the core has a torus or donut shape, either with a circular or rectangular cross section. This geometry has minimum leakage flux and emits minimum electromagnetic interference (EMI).
- A coil with a core that is a straight rod or other non-loop shape is called the open-core coil. It has a magnetic field and a lower inductance than a closed core, but is often used to prevent core magnetic saturation.
A coil without a ferromagnetic core is called an air-core coil . These include rolls of rolls on plastics or other nonmagnetic shapes, as well as actual coils having a blank air space inside their scrolls.
Roll type
Coils can be classified by the frequency of currents designed to operate by:
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- Direct current or DC coil or electromagnet operates with a steady direct current in the windings
- Audio-frequency or AF coil, inductor or transformer operates with alternating current in audio frequency range, less than 20 kHz
- Radio-frequency or RF coils, inductors or transformers operate with alternating current in radio frequency range, above 20 kHz
Coils can be classified by function:
Electromagnet
Electromagnets are coils that produce magnetic fields for some external uses, often for exerting mechanical forces on something. Some special types:
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- Solenoid - electromagnet in the form of a hollow helix straight from the wire
- Motor windings and generators - iron core electromagnets on the rotor or stator of electric motors and generators acting on one another to rotate the shaft (motor) or generate an electric current (generator)
- Field scroll - iron-core coil that produces a fixed magnetic field to act on the armature winding.
- Armature rolls - iron-core coils are acted upon by a magnetic field from a winding field to create torque or induce a voltage to generate power (generator)
- Helmholtz coil, Maxwell coil - an air core coil that serves to cancel an external magnetic field
- The degaussing coil - the coil used to demagnetize the section
- Voice coil - a coil used in a moving winding loudspeaker, hanging between the magnetic poles. When an audio signal is passed through the coil, it vibrates, moving the speaker cone attached to create sound waves. Instead it is used in dynamic microphones, where the sound vibration is intercepted by something like a physical transfer diaphragm to a voice coil immersed in a magnetic field, and the terminal end of the coil then provides the electrical analog of the vibration.
Inductor
The inductor or reactor is a coil that produces a magnetic field that interacts with the coil itself, to induce a rear EMF that opposes the change of current through the coil. Inductors are used as circuit elements in electrical circuits, to store temporary energy or withstand current changes. Some types:
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- Tank coil - the inductor used in the tuned circuit
- Choke - an inductor used to block high frequency AC while allowing via low frequency AC.
- The loading coil - the inductor used to add the inductance to the antenna, to make it resonate, or to the cable to prevent signal distortion.
- Adjustable variables consisting of two coils in series, the outer stationary coil and the second in it that can be rotated so that the magnetic axis is in the same direction or opposed.
- The flyback transformer - Although called a transformer, this is actually an inductor that serves to store energy in switching power supplies and horizontal deflection circuits for CRT televisions and monitors
- Groupable reactors - iron-core inductors used to control AC power by varying core saturation using DC control voltage in auxiliary winding.
- Inductive ballasts - inductors used in gas-discharge lamp circuits, such as fluorescent lamps, to limit current through lamps.
Transformer
The transformer is a device with two or more magnetic reels (or parts of single windings). The time flow varies in one coil (called the primary winding) producing a magnetic field that induces a voltage in the other coil (called the secondary winding). Some types:
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- Distribution transformers - Transformers in power grids that convert high voltage from power lines to lower voltages used by utility customers.
- Autotransformer - transformer with only one coil. Different parts of entanglement, accessed by tapping, acts as the primary and secondary windings of the transformer.
- Toroidal transformer - essentially shaped toroid. This is a common form of use because it reduces the leakage flux, resulting in poor electromagnetic interference.
- Induced coil or trembler coil - an initial transformer using a vibrating interrupter mechanism to break the main current so it can operate from DC current.
- Ignition coil - induction coil used in an internal combustion engine to create high voltage pulses to ignite spark plugs that start fuel combustion.
- Balun - a matching transformer with a balanced transmission line to an unbalanced channel.
- Bifilar coil - twist coil with two parallel lines and close proximity. If the AC current is passed in the same direction, the magnetic flux will increase, but if the same current in opposite direction passes the winding, the opposite flux will cancel, resulting in a zero flux in the core. So no voltage will be induced in the third winding at the core. These are used in instruments and devices such as Ground Fault Interrupters. They are also used in low wirewound resistor inductance for use on RF frequencies.
- Audio transformers - Transformers used with audio signals. They are used for impedance matching.
- Hybrid coil - a special audio transformer with 3 windings used in the telephone circuit to convert between two-wire and four-wire circuits
Power engine
Electric machines such as motors and generators have one or more coils that interact with a moving magnetic field to convert electrical energy into mechanical energy. Often a machine will have a single coil through which it passes most of the engine power ("armature"), and the second winding which provides the magnetic field of the rotating element ("field scrolling") that may be connected by a brush or a ring slip to an external source of electric current. In an induction motor, the "rotor" field winding is energized by the relatively slow motion between the winding winding and the rotating magnetic field generated by the stator windings, which induces the draw current required in the rotor.
Transducer scroll
This is a coil used to translate a time-varying magnetic field to an electrical signal, and vice versa. Some types:
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- Sensor or pickup coil - this is used to detect magnetic fields that vary external times
- Inductive sensor - a coil that senses when a magnet or iron object passes through it
- Record head - the coil used to create a magnetic field to write data to magnetic storage media, such as magnetic tape, or hard disk. Instead it is also used to read data in the form of magnetic field changes in the medium.
- Induction heating coils - AC coils used to heat objects by inducing eddy currents in them, a process called induction heating.
- Loop antenna - a coil that acts as a radio antenna, to convert radio waves into electric current.
- Rogowski coil - toroidal coil is used as an AC gauge
- Pickup instruments - coils used to produce audio signal output in electric guitar or electric bass.
- Gate flux - sensor coil used in magnetometer
- Magnetic phonograph cartridge - a sensor in a recording player that uses a coil to translate the vibration of the needle into the audio signal in rotating the phonograph record.
There are also types of coils that do not fit into this category.
Technology winding
References
Further reading
- Querfurth, William, " Coil winding, description of winding coil procedure, winding machine and related equipment for electronics industry " (2d ed.). Chicago, G. Stevens Mfg. Co., 1958.
- Weymouth, F. Marten, " Armature drum and commutator (theory and practice): a complete treatise on the theory and construction of drum reels, and commutators for closed coil armatures, together with full rae  © sumÃÆ' © from some of the main points involved in their design, and the exposition of the armor and trigger reactions ". London, "The Electrician" Printing and Publishing Co., 1893.
- " Coil scroll ". International Coil Winding Association.
- Chandler, R. H., " Review of coil layers, 1970-76 ". Braintree, R. H. Chandler Ltd, 1977.
External links
- Coil Inductance Calculator Online calculator to determine single layer and multilayer coil inductance
- R. Clarke, " Producing wound components ". Surrey.ac.uk, 2005 October 9
Source of the article : Wikipedia
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