This article takes an in depth look at solenoid coils.
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A solenoid coil is a common electrical component that uses a wire that is tightly wrapped around a core, usually made of metal, to generate an electromagnetic field. When an electrical current is passed through the coil, the electromagnetic field that is created provides energy for linear motion. Solenoid coils are one of the simplest forms of linear actuation devices.
Solenoid coils are a very versatile tool that can be found in production machines, toys, appliances, and various forms of automated equipment. They are normally used to automatically turn an application on or off. A movable armature in the coil is activated as voltage passes through it; this causes the armature to increase its linkage to activate whatever it is attached to.
The applications of solenoid coils for industrial processes widely vary; some are an important part of a locking mechanism while others are the central part of automated production machines. In most cases, a solenoid coil for industrial use is the method for activating hydraulic and pneumatic valves.
Solenoid coils are found as part of an automatic locking mechanism, such as door locks for high security areas and restricted access rooms. When the locking mechanism is in the locked position, the solenoid coil is not charged. With the addition of electrical energy, the solenoid coil activates and unlocks.
Solenoid coils are an essential part of medical equipment since medical devices have to be precise, accurate, and reliable. Manufacturers are required to adhere to exceptionally restrictive standards to prevent any possibility of solenoid coil failure. In dialysis machines, there are two solenoid coils that control blood flow. Solenoid coils can be found in dosing machines that control the flow of medications to patients. Other medical devices that use solenoid coils include oxygen delivery systems, diagnostic equipment, patient monitoring, respirators, and gas chromatography.
Solenoid coils are an essential part of the increase in automation in the production of automobiles. They are used for interlocking in the gearbox drive selector, an important part of the drive selection process. Solenoid coils are found in air conditioning controls, entertainment mechanisms, and security systems.
A solenoid coil for an irrigation system manages the flow of water by turning it on and off to stop or release water into the system. There are several types of solenoid coils used for irrigation systems that are capable of fitting underground. They have a screw attached to the plumbing and wires for electrical activation.
Irrigation solenoid coils are attached to an electronic timer that is set to water lawns at a specific time. In some cases, irrigation solenoid coils can get blocked by dirt, soil, or other particles; this can disrupt their function and force them to stay open.
Aircraft have a separate power distribution bus for electronics equipment; this is depowered when the starter on the aircraft is activated to prevent voltage spikes. A solenoid coil connects the avionics bus, which connects the electronics equipment, to the main power bus. It is activated when the starter is engaged and depowers the avionics bus during start up.
A solenoid coil on a hydraulic system opens, closes, and changes the directional flow of fluid in the system. They are low power switches that open and close pilot valves that control the main valve that applies pressure to the connected piston or diaphragm. The choice of hydraulic solenoid coil is affected by its voltage and power consumption.
The normal solenoid coil has an open or closed position. Those that are closed position close the flow when activated. In the case of open solenoid coils, they open when activated to allow the fluid to flow.
A pneumatic system uses a three way, two position solenoid coil that allows fluid to be diverted from one channel to another channel and is capable of controlling cylinders bi-directionality. Some pneumatic systems use a five way, three position solenoid coil that has two coils.
In a pinball machine, the solenoid coil makes the ball shoot away when it hits the bumper and gives the ball an extra amount of explosive force. The solenoid coil in a pinball machine retracts the metal rod that drives the ball, then thrusts forward. They are also used to power the flippers used to push the ball back up the playing surface.
To ensure proper performance of the machine, the solenoid coil of a pinball machine is powered for a fraction of a second to avoid overload and damage to the coil.
The construction of a solenoid coil involves a wire, copper or aluminum, that is wound around a hollow form. Coils can have direct or alternating currents, able to work with any voltage with 6, 12, 24, 120, and 220 being the most common. Low voltage coils of less than 24 volts are used for small jobs while higher voltage coils over 24 volts are used for industrial applications and heavy machinery.
The two most common types of solenoid coils are tape wrapped and encapsulated or molded. Tape wrapped solenoid coils are used in less hostile environments where there is little chance of exposure to solvents and chemicals, such as clocks, timers, pneumatic systems, and electronic circuits.
Encapsulated coils are enclosed in a tightly sealed material such as polyester, rubber, or epoxy. Sealing a solenoid coil gives it insulation and dielectric strength as well as enhanced structural integrity and impact resistance. The protection of the coil through encapsulation allows it to be used in harsh and stressful conditions.
Copper wire is the most common type of wire that is used to construct a solenoid coil. There are other types of wire available, but none of them have the same conductivity and pliability as copper. The classes of copper wire that have the characteristics and properties needed for solenoid coils are classes F, H, and N.
A key factor in the use of copper wire is its diameter. If the wire is too fine, it will increase the coils resistance and decrease its productive performance as well as cause the coil to burn out easily.
Class F copper windings can withstand temperatures exceeding 155° C and work well in ambient temperatures of 20° C with media up to 100° C.
Class H windings can withstand temperatures in excess of 180° C and operate well in 50° C with media at 180° C.
Class N windings work well at temperatures that exceed 200° C and an ambient temperature of 80° C with media up to 200° C.
The bobbin holds the wire in place and provides a location to secure the lead wires to avoid strain. The functions of the bobbin, aside from being the wire holder, include locating and guiding the movement of the components as well as controlling the solenoid‘s stroke. The bobbin is exceptionally durable and has a low friction surface. Bobbins can have connectors such as DIN connectors for the supply of electrical current.
The winding of a solenoid coil is determined by the circuit requirements, inductance value, and the diameter of the bobbin. The number of windings determines the strength of the solenoid‘s magnetic field. Its inductance will vary according to the square of the number of coil turns.
Increasing the number of coils adds more field lines and makes for a stronger electromagnetic field. As the number of loops of wire increases, the strength of the electromagnetic field increases. So, the strength of the field is affected by the number of coils, wire used, and the thickness of the wire. As resistance drops, more current is able to flow through, producing a larger magnetic field.
The core of a solenoid coil can be made of any type of ferromagnetic metal, which increases the coil's magnetic power. Solenoid coils can work without a core; this can be seen in those that have an air core. The core determines how strong the magnetic field will be; some cores increase the magnetic strength by 100 times.
Air cores are made of glass or plastic and are unable to increase the strength of the magnetic field. The benefit of air cores is their ability to be very efficient at high frequencies with the capability of reaching one gigahertz (GHz). A metal core can only reach 100 megahertz (MHz).
The types of cores are:
There are two methods for protecting the wires of a solenoid: wrapping and encapsulating. The variations between the two types are easily distinguishable since wrapped solenoid coils are enclosed with paper or tape while encapsulated are embedded in some form of solid, non-porous material.
Wrapped solenoid coils have adhesive tape or paper wrapped around the magnetic wires. The majority of wrapped coils are protected by insulated tape.
Encapsulated solenoid coils are protected by solid materials such as epoxy, rubber, different forms of polyester, and plastic. These types of solenoids are referred to as molded and are capable of withstanding harsh and hazardous conditions.
DIN stands for Deutsches Institut für Normung, which in English means the German Institute for Standardization. Though DIN standards are used for electronics, they are also used for a wide variety of other products. In the case of solenoid coils, DIN connectors are used in place of lead wires and have a male connection to be inserted into a female plug. They form a more solid link to the application; this enhances coil exchange.
The most common use of DIN connectors is with encapsulated solenoid coils since they can easily be included as part of the bobbin.
The basic purpose of a solenoid coil is to convert electrical energy into mechanical energy to supply linear motion. The structure of a solenoid coil includes a coil of wire that is wrapped around a piston made of a ferromagnetic metal. The benefit of a solenoid coil, when compared to a magnet, is the fact that it can be turned off; this makes it perfect for switches, valves, and automated devices.
As with all forms of magnets, a solenoid coil has positive and negative poles that can attract or repel any form of material that is sensitive to the forces of a magnet. With a solenoid, the magnetic field causes the core or piston to move forward or backward to activate an application or turn it off.
There are two key components to a solenoid coil: its magnetic field and electricity. Magnets can be pointed at metal objects and change the direction of the object or its position. The problem with a magnet is that once magnetized, it cannot be turned off, and it continually emits its magnetic field.
This particular problem is not part of the operation of a solenoid coil. Since its magnetic field is activated by electricity, it is possible to control when and how the magnetic field can be used.
All wires produce a weak magnetic field when electricity passes through them. To enhance this property and create a strong magnetic field, wires for a solenoid coil are wound into a coil where each curled wire produces the same magnetic field as a single straight wire.
Every electrical device requires a closed loop between the thing being powered and the power source. A switch is a safe and convenient way to break the connection between the device being powered and its source of power. As the need for power increases, the size of the switch to break the connection has to increase as well.
Though the amount of power increases with the size of the switch, it still only takes a small amount of energy to turn the switch on and off. The use of a solenoid can provide the necessary energy since its operation does not require much energy. In essence, a 24 volt solenoid can easily turn on a 240 volt machine.
If a normal switch were connected to a large piece of equipment, it would require a huge wire with a very large diameter to provide the necessary power to turn on the machine. Since a solenoid does not require the same amount of power as the device it is turning on, the size of the wire can be smaller and less expensive.
The back-and-forth motion of a solenoid coil either allows an application to activate or turns it off. As simplistic as it may be, a solenoid makes the activation of large pieces of equipment easy without the need for excessive energy.
By varying the design of a solenoid coil, different objectives can be achieved. In the case of a locked door, a solenoid can remain activated to keep the door locked. Once an electric current moves through the coil, the spring of the solenoid coil retracts the plunger and unlocks the door.
Proportional solenoid coils convert an electric signal into proportional mechanical force; this allows a variance in the position and force relative to the current level. The uses for a proportional solenoid coil include the regulation of flow rates by changing the position of the plunge of the valve.
There is an endless number of solenoid coils with types available for every possible application. The many kinds of coils vary in accordance with their design, materials, and use. Regardless of the variations and different uses, all solenoid coils operate using the same electrical principles.
Solenoid coils are commonly used as solenoid valve coils for the controlling of fluids. They are also found in automated equipment and as a part of robotic operations. In addition to categorization by wrapped and encapsulated, solenoid coils are further divided between alternating current (AC) and direct current (DC). Which of the two currents is used depends on a variety of factors that rely heavily on the application for which the coil is being used.
An AC solenoid coil can deliver a large amount of force in the first stroke; this is due to the high input of current when the coil is turned on. This particular feature allows this type of coil to deliver more strokes. AC laminated solenoid coils come in different configurations and produce a buzzing sound. They are ideal for applications that require immediate action, such as medical equipment, vehicles, printers, and appliances.
The C frame of a DC C frame solenoid coil has an open frame to provide linear motion. It is the simplest form of solenoid and has a cost effective design but provides exceptionally high performance. It is available in a push or pull configuration and is used for simple applications such as circuit breakers, scanners, coin counters, and point of sale devices.
A linear solenoid coil is also known as a linear electromechanical actuator (LEMA) and can be continuously energized or be an on and off switch. LEMAs can be designed as a proportional solenoid coil that changes the plunger‘s position in relation to the power input. The name linear solenoid coil relates to the linear movement of the plunger when the coil is activated.
Solenoid coils are normally linear devices that move back-and-forth. Rotary solenoid coils convert linear motion into rotary motion through the use of three ball bearings.
When the coil is energized, the armature is pulled toward the stator and rotated through an arc. Rotational solenoid coils produce an angular or rotary motion in a clockwise or counter clockwise direction or in both directions.
The movement of a rotary solenoid coil can be 25o, 35o, 45o, 60o, and 90o or multiple movements at certain angles. The rotary motion can be produced when the coil is energized, not energized, or when there is a change in the polarity of the electromagnetic field.
A DC D frame solenoid coil is enclosed in two D frames on two sides. This type of frame allows for slightly higher force output and greater resistance to environmental factors. D frame solenoid coils have an economical design for high volume applications and continuous duty and are available for on and off applications.
The many sizes and stroke options of a DC - D frame solenoid coil can provide service for several million cycles.
The purpose of a solenoid valve coil is to control fluids in tubes, ducts, and pipes. There are several varieties of solenoid valve coils that are designed to meet the needs of various fluid flow applications.
Direct acting solenoid valve coils have a plunger that closes a small opening without the use of force. It is a fast acting coil that can operate under pressure and can be an open or closed valve coil.
A pilot operated solenoid valve coil is referred to as an indirect operating coil and uses pressure across the valve port to open or close the valve opening. The coil opens when it is energized and is kept closed by the system‘s pressure.
A two way solenoid valve coil has two ports that can open or close to control the flow. They are used where release and restriction of fluids are needed—in air compressors for example.
A three way solenoid coil has three ports and two openings that open, alternating according to the requirements of the coil. Two of the ports are inlet ports while the other single port is an outlet port. It is capable of controlling two different fluids.
A four way solenoid valve coil has an additional port. Two of the ports are inlet while the other two are outlets. They are used to operate double acting solenoid valve actuators.
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