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Operation of a 12 A relay Automotive-style miniature relay, dust cover is taken off A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal.
The first relays were used in long distance telegraph circuits as amplifiers: Relays were used extensively in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor.
Solid-state relays control power circuits with no moving partsinstead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called " protective relays ".
Magnetic latching relays require one pulse of coil power to move their contacts in one direction, and another, redirected pulse to move them back. Repeated pulses from the same input have no effect. Magnetic latching relays are useful in applications where interrupted power should not be able to transition the contacts.
Magnetic latching relays can have either single or dual coils. On a single coil device, the relay will operate in one direction when power is applied with one polarity, and will reset when the polarity is reversed.
On a dual coil device, when polarized voltage is applied to the reset coil the contacts will transition. AC controlled magnetic latch relays have single coils that employ steering diodes to differentiate between operate and reset commands. A simple device, which is now called a relay, was included in the original telegraph patent of Samuel Morse.
The "cradle" term refers to the shape of the relay's armature. A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core a solenoidan iron yoke which provides a low reluctance path for magnetic flux, a movable iron armatureand one or more sets of contacts there are two contacts in the relay pictured.
The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. The armature is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open.
Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke.
This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board PCB via the yokewhich is soldered to the PCB.
When an electric current is passed through the coil it generates a magnetic field that activates the armature, and the consequent movement of the movable contact s either makes or breaks depending upon construction a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open.
When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly.
In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing. When the coil is energized with direct currenta diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to semiconductor circuit components.
Such diodes were not widely used before the application of transistors as relay drivers, but soon became ubiquitous as early germanium transistors were easily destroyed by this surge. Some automotive relays include a diode inside the relay case.
· Chemistry Collisions, Reactions, and Transport ©David Ronis This distance is called the mean free path. Note that it only depends on the number density of Consider a gas containing twokinds of molecules in which there is a concentration gradient; i.e., the density of molecules per unit volume,ni(z)ashio-midori.com The constant μ is the mean free path and is the average (mean) distance traveled by a molecule between collisions.
The mean free path of an oxygen gas molecule under a pressure of 1 atmosphere at 0° C is about 6 × 10 -6 cm (2 × 10 −6 inch). · The mean free path (MFP) is the average distance which a molecule of a gas- or vapour travels before it collides with another molecule.
At high vacuum, these distances become very large, so the particles collide only with the walls of the vacuum ashio-midori.com Black Body Radiation. Michael Fowler, University of Virginia. Query 8: but they constantly bump into things — they have a short mean free path.
When they bump, they cause vibration, like balls hitting bumpers in a pinball machine, so they give up kinetic energy into heat. Thus molecules in a gas have average kinetic energy 3 2 k B T, ashio-midori.com gas can be understood by applying Newton's law to the microscopic motion of the molecules making up the gas and that a comparison between the Newtonian prediction and the ideal gas law can provide a function which describes the distribution of molecular velocities.
· A relay is an electrically operated ashio-midori.com relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state ashio-midori.com are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one ashio-midori.com://ashio-midori.com