The awkward case of 'his or her'. More word puzzles to rack your brain. Test your knowledge - and maybe learn something along the way. The dictionary has been scrambled—can you put it back together? Definition of switch off. Learn More about switch off. Resources for switch off Time Traveler! Explore the year a word first appeared.
Dictionary Entries near switch off switch line switch lock switchman switch off switch on switchover switch plant. Statistics for switch off Look-up Popularity. More from Merriam-Webster on switch off Nglish: Comments on switch off What made you want to look up switch off? Get Word of the Day daily email! Need even more definitions? A History Focusing in on what we do best. When turned on, an incandescent lamp draws a large inrush current of about ten times the steady-state current; as the filament heats up, its resistance rises and the current decreases to a steady-state value.
A switch designed for an incandescent lamp load can withstand this inrush current. Wetting current is the minimum current needing to flow through a mechanical switch while it is operated to break through any film of oxidation that may have been deposited on the switch contacts. Providing a sufficient amount of wetting current is a crucial step in designing systems that use delicate switches with small contact pressure as sensor inputs.
Failing to do this might result in switches remaining electrically "open" due to contact oxidation. The moving part that applies the operating force to the contacts is called the actuator , and may be a toggle or dolly , a rocker , a push-button or any type of mechanical linkage see photo. A switch normally maintains its set position once operated.
A biased switch contains a mechanism that springs it into another position when released by an operator. The momentary push-button switch is a type of biased switch. The most common type is a "push-to-make" or normally-open or NO switch, which makes contact when the button is pressed and breaks when the button is released. Each key of a computer keyboard, for example, is a normally-open "push-to-make" switch. A "push-to-break" or normally-closed or NC switch, on the other hand, breaks contact when the button is pressed and makes contact when it is released.
An example of a push-to-break switch is a button used to release a door held closed by an electromagnet. The interior lamp of a household refrigerator is controlled by a switch that is held open when the door is closed. A rotary switch operates with a twisting motion of the operating handle with at least two positions. One or more positions of the switch may be momentary biased with a spring , requiring the operator to hold the switch in the position.
Other positions may have a detent to hold the position when released. A rotary switch may have multiple levels or "decks" in order to allow it to control multiple circuits.
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One form of rotary switch consists of a spindle or "rotor" that has a contact arm or "spoke" which projects from its surface like a cam. It has an array of terminals, arranged in a circle around the rotor, each of which serves as a contact for the "spoke" through which any one of a number of different electrical circuits can be connected to the rotor. The switch is layered to allow the use of multiple poles, each layer is equivalent to one pole.
Usually such a switch has a detent mechanism so it "clicks" from one active position to another rather than stalls in an intermediate position. Thus a rotary switch provides greater pole and throw capabilities than simpler switches do. Rotary switches were used as channel selectors on television receivers until the early s, as range selectors on electrical metering equipment, as band selectors on multi-band radios and other similar purposes. In industry, rotary switches are used for control of measuring instruments, switchgear , or in control circuits. For example, a radio controlled overhead crane may have a large multi-circuit rotary switch to transfer hard-wired control signals from the local manual controls in the cab to the outputs of the remote control receiver.
A toggle switch is a class of electrical switches that are manually actuated by a mechanical lever , handle, or rocking mechanism. Toggle switches are available in many different styles and sizes, and are used in numerous applications. Many are designed to provide the simultaneous actuation of multiple sets of electrical contacts , or the control of large amounts of electric current or mains voltages.
The word "toggle" is a reference to a kind of mechanism or joint consisting of two arms, which are almost in line with each other, connected with an elbow-like pivot. However, the phrase "toggle switch" is applied to a switch with a short handle and a positive snap-action, whether it actually contains a toggle mechanism or not. Similarly, a switch where a definitive click is heard, is called a "positive on-off switch".
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Multiple toggle switches may be mechanically interlocked to prevent forbidden combinations. In some contexts, particularly computing , a toggle switch, or the action of toggling, is understood in the different sense of a mechanical or software switch that alternates between two states each time it is activated, regardless of mechanical construction. For example, the caps lock key on a computer causes all letters to be generated in capitals after it is pressed once; pressing it again reverts to lower-case letters. Switches can be designed to respond to any type of mechanical stimulus: Many switches are operated automatically by changes in some environmental condition or by motion of machinery.
A limit switch is used, for example, in machine tools to interlock operation with the proper position of tools. In heating or cooling systems a sail switch ensures that air flow is adequate in a duct. Pressure switches respond to fluid pressure. The mercury switch consists of a drop of mercury inside a glass bulb with two or more contacts. The two contacts pass through the glass, and are connected by the mercury when the bulb is tilted to make the mercury roll on to them. This type of switch performs much better than the ball tilt switch, as the liquid metal connection is unaffected by dirt, debris and oxidation, it wets the contacts ensuring a very low resistance bounce-free connection, and movement and vibration do not produce a poor contact.
These types can be used for precision works.
It can also be used where arcing is dangerous such as in the presence of explosive vapour as the entire unit is sealed. Knife switches consist of a flat metal blade, hinged at one end, with an insulating handle for operation, and a fixed contact. When the switch is closed, current flows through the hinged pivot and blade and through the fixed contact.
Such switches are usually not enclosed. The knife and contacts are typically formed of copper , steel , or brass , depending on the application. Fixed contacts may be backed up with a spring. Several parallel blades can be operated at the same time by one handle. The parts may be mounted on an insulating base with terminals for wiring, or may be directly bolted to an insulated switch board in a large assembly. Since the electrical contacts are exposed, the switch is used only where people cannot accidentally come in contact with the switch or where the voltage is so low as to not present a hazard.
Knife switches are made in many sizes from miniature switches to large devices used to carry thousands of amperes.
In electrical transmission and distribution, gang-operated switches are used in circuits up to the highest voltages. The disadvantages of the knife switch are the slow opening speed and the proximity of the operator to exposed live parts. Metal-enclosed safety disconnect switches are used for isolation of circuits in industrial power distribution.
Sometimes spring-loaded auxiliary blades are fitted which momentarily carry the full current during opening, then quickly part to rapidly extinguish the arc. A footswitch is a rugged switch which is operated by foot pressure. An example of use is in the control of a machine tool, allowing the operator to have both hands free to manipulate the workpiece.
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The foot control of an electric guitar is also a footswitch. These crossover switches only have four terminals rather than six. Two of the terminals are inputs and two are outputs.
When connected to a battery or other DC source, the 4-way switch selects from either normal or reversed polarity. Such switches can also be used as intermediate switches in a multiway switching system for control of lamps by more than two switches. In building wiring, light switches are installed at convenient locations to control lighting and occasionally other circuits.
By use of multiple-pole switches, multiway switching control of a lamp can be obtained from two or more places, such as the ends of a corridor or stairwell. A wireless light switch allows remote control of lamps for convenience; some lamps include a touch switch which electronically controls the lamp if touched anywhere. In public buildings several types of vandal resistant switches are used to prevent unauthorized use. Slide switches are mechanical switches using a slider that moves slides from the open off position to the closed on position. A relay is an electrically operated switch.
Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching—often a silicon-controlled rectifier or triac. The analogue switch uses two MOSFET transistors in a transmission gate arrangement as a switch that works much like a relay, with some advantages and several limitations compared to an electromechanical relay. The power transistor s in a switching voltage regulator , such as a power supply unit , are used like a switch to alternately let power flow and block power from flowing.
Many people use metonymy to call a variety of devices "switches" that conceptually connect or disconnect signals and communication paths between electrical devices, analogous to the way mechanical switches connect and disconnect paths for electrons to flow between two conductors. Early telephone systems used an automatically operated Strowger switch to connect telephone callers; telephone exchanges contain one or more crossbar switches today. Since the advent of digital logic in the s, the term switch has spread to a variety of digital active devices such as transistors and logic gates whose function is to change their output state between two logic levels or connect different signal lines, and even computers, network switches , whose function is to provide connections between different ports in a computer network.
The term 'switched' is also applied to telecommunications networks , and signifies a network that is circuit switched , providing dedicated circuits for communication between end nodes, such as the public switched telephone network. The common feature of all these usages is they refer to devices that control a binary state: From Wikipedia, the free encyclopedia. For the GUI widget, see Cycle button. For the video game console, see Nintendo Switch. For other uses, see Switch disambiguation. Archived from the original on Suppressed Arcing " pdf.
Switch - Wikipedia
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