In engineering, a solenoid is a device that converts electrical energy to mechanical energy, using an electromagnet formed from a coil of wire. The device creates a magnetic field from electric current, and uses the magnetic field to create linear motion. A solenoid is a type of electromagnet consisting of coiled copper wire wound tightly into a helix, a mobile plunger made of magnetic material, and an iron or steel housing. As electric current moves through a coil, the solenoid generates a magnetic field and transforms magnetic energy into mechanical motion. In electromagnetic technology, a solenoid is an actuator assembly with a sliding ferromagnetic plunger inside the coil. Without power, the plunger extends for part of its length outside the coil; applying power pulls the plunger into the coil. Electromagnets with fixed cores are not considered solenoids. In simple terms, a solenoid converts electrical energy into mechanical work. Typically, it has a multiturn coil of magnet wire surrounded by a frame, which is also a magnetic flux carrier to enhance its efficiency. In engineering, the term may also refer to a variety of transducer devices that convert energy into linear motion, more sophisticated than simple two–position actuators. The term "solenoid" also often refers to a solenoid valve, an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, a specific type of relay that uses an internal electromechanical solenoid to operate an electrical switch; for example, an automobile starter solenoid or linear solenoid. A solenoid bolt is a type of electromechanical locking mechanism.
Applications
Electromechanical solenoid
Electromechanical solenoids consist of an electromagnetically inductive coil, wound around a movable steel or iron slug (termed the armature). The coil is shaped such that the armature can be moved in and out of the space in the center of the coil, altering the coil's inductance and thereby becoming an electromagnet. The movement of the armature is used to provide a mechanical force to some mechanism, such as controlling a solenoid valve. Although typically weak over anything but very short distances, solenoids may be controlled directly by a controller circuit, and thus have very quick reaction times. The force applied to the armature is proportional to the change in inductance of the coil with respect to the change in position of the armature and the current flowing through the coil (see Faraday's law of induction). The force applied to the armature will always move the armature in a direction that increases the coil's inductance. Electromechanical solenoids are commonly seen in electronic paintball markers, pinball machines, dot matrix printers, and fuel injectors. Some residential doorbells make use of electromechanical solenoids, whereby electrification of the coil causes the armature to strike metal chime bars.
Push and pull solenoids
Push and pull solenoids are common catalog items, usually in a tubular construction. They consist of a bobbin-wound coil, steel plunger, cylindrical case and end pieces, one of which is a stator pole. Each type is similar to the other in construction except that the pull type has means for attaching to the plunger and pulls the attached load toward the solenoid. The push type has a push-pin projecting out of the solenoid to push the load away from the solenoid. Magnetically they are the same; i.e., internally the magnetic field attracts the plunger toward the stator pole piece. Most solenoids do not use magnetic repulsion between the magnetic pole and plunger to do the pushing except in rare instances. Some permanent magnet types operate by simultaneous attraction and repulsion of the plunger in the same direction in order to actuate (and are bi-directional by reversing the coil's electrical polarity). Common push or pull solenoids move in one direction only upon being energized. A spring or other means is required to move the plunger to its de-energized position. Other constructions utilize a C- or D-shaped frame of bent flat steel and the coil may be visible. The efficiency of these types are due to their steel outer frames which enclose the magnetic flux around the coil (end to end) to focus the flux at the air gap between the plunger and stator pole.
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