Switch
A switch is a device used in electrical engineering that has the ability to connect or disconnect a circuit's conducting line, halting the flow of electricity, or rerouting it to another conductor. An electromechanical switch, which has one or more sets of moveable electrical contacts coupled to external circuits, is the most popular type of switch. Current can flow between two contacts when they are touching, but it cannot when the contacts are apart.
The contacts on switches can work simultaneously, sequentially, or alternately, and they can have many sets of contacts that are all operated by the same knob or actuator. A switch can sense the location of a machine part, liquid level, pressure, or temperature, like a thermostat, or it can be manually activated, like a light switch or a keyboard button. Toggle switches, rotary switches, mercury switches, push-button switches, reversing switches, relays, and circuit breakers are only a few examples of the many specialized types.
Lighting control is a frequent application in which several switches may be linked into a single circuit to provide practical control of light fixtures. To avoid destructive arcing when they are opened, switches in high-powered circuits need to be specially built.
Description
A manually operated electromechanical switch having one or more sets of electrical contacts connected to external circuits is the most common type of switch. There are two possible states for each set of contacts: "closed," which means the contacts are in contact and electricity can flow between them, or "open," which means the contacts are apart and the switch is not conducting. There are numerous types of actions that can be used, but often, a "alternative action" (flipping the switch for continuous "on" or "off") or "momentary" (pushing for "on" and releasing for "off") type mechanism is used to switch between these two states (open or closed).
A switch can be directly operated by a person to regulate the flow of power in a circuit, such as a light switch, or to send a control signal to a system, like a computer keyboard button. Automatically operated switches can be used to regulate machine motions, such as to signal when a garage door has fully opened or when a machine tool is ready to accept a new piece of work. Switches can act as sensors in a process and be used to automatically control a system by being activated by process variables like pressure, temperature, flow, current, voltage, and force.
When closed, an ideal switch would have no voltage drop and no voltage or current rating restrictions. When changing states, there would be no rise time or fall time, and it would do it without "bouncing" between the on and off positions.
Practical switches fall short of this ideal because of contact resistance, constraints on the current and voltage they can handle, finite switching times, and other issues caused by roughness and oxide layers. The ideal switch is frequently employed in circuit analysis because it makes the system of equations to be solved incredibly simple. However, this can result in a less precise solution. In order to build large switch networks, such as those used in telephone exchanges, the consequences of non-ideal features must be treated theoretically.
Contacts
The simplest type of switch comprises two contacts that are linked to an external circuit and touch to complete (create) the circuit and separate to open (break) the circuit. The contacts are often made of metal. Because the majority of metals develop insulating oxides that would prohibit the switch from functioning, the contact material is chosen for its resistance to corrosion. Additionally, contact materials are selected for their electrical conductivity, mechanical strength, hardness (resistance to abrasive wear), affordability, and low toxicity. The contact resistance and wetness current of a mechanical switch are determined by the growth of oxide layers at the contact surface, surface roughness, and contact pressure.
Noble metals are occasionally used to plate connections because of their good conductivity and corrosion resistance. They might be made to rub against one another to remove any contaminants. Occasionally, nonmetallic conductors like conductive polymers are utilized. For a specific switch design, a minimum wetting current may be specified to avoid the growth of insulating oxides.
Contact terminology
Switches are categorized in electronics based on how their contacts are set up. When current can move from one contact to the other, two contacts are said to be "closed." When an insulating air gap separates the contacts, they are termed to be "open," and at normal voltages, no current can pass between them. Additionally, the words "create" for contact closure and "break" for contact opening are frequently used.
Switch contact variants are frequently referred to by the names pole and throw. The number of electrically independent switches that are each under the direction of a single physical actuator are referred to as "poles." A "2-pole" switch, for instance, has two different parallel sets of contacts that open and close simultaneously using the same mechanism. The number of "throws" refers to how many other wire path options, except "open," the switch can select for each pole. One pair of contacts on a single-throw switch can be either closed or open. A contact on a triple-throw switch can be linked to any one of three other contacts, while a contact on a double-throw switch can be connected to any of two other contacts.
A push-button switch, for example, has contacts that are either normally open (abbreviated "n.o." or "no") until the switch is operated to shut them, or normally closed ("n.c." or "nc") until the switch action opens them. Changeover switches and double-throw switches are terms used to describe switches containing both sorts of contacts. These can either be "break-before-make" (BBM or non-shorting) or "make-before-break" (MBB or shorting), which temporarily connects one circuit before closing the other.
The abbreviations "single-pole, single-throw" (SPST) and "single-pole, double-throw" (SPDT), which connect either of two terminals to the common terminal, are derived from these words and are used to refer to the many switch types used in the electronics industry. Names used in electrical power wiring (i.e., wiring of homes and buildings by electricians) typically end in "-way," but the terminologies used range between British English and American English (i.e., the terms two way and three way are used with different meanings).
A number (e.g., 3PST, SP4T, etc.) or, in some situations, the letter "T" (for "triple") or "Q" can be used to designate switches with more poles or throws (for "quadruple"). To avoid misunderstanding, the terms SPST, SPDT, and intermediate will be used throughout the remainder of this paper.
Contact bounce
Mechanical switches and relays frequently experience contact bounce (also known as chatter), which is an issue brought on by electrical contact resistance (ECR) occurrences at interfaces. Typically, springy metals are used to make switch and relay contacts. The momentum and elasticity of the contacts cause them to bounce apart once or more times before coming into steady contact when they come into touch. Instead of a smooth transition from zero to full current, the outcome is a rapidly pulsed electric current. In power circuits, the effect is typically unimportant, but it can cause issues in some analogue and logic circuits that react quickly enough to mistake the on/off pulses for a data stream.
Chatter can be prevented in the design of micro-contacts by reducing the production of passivated layers on metallic surfaces and managing surface structure (surface roughness).
Mercury-wetted contacts can be used to eliminate the effects of contact bounce, however they are no longer often used due to the risks associated with mercury. Alternately, contact circuit voltages can be low-pass filtered to minimize or completely get rid of repeated pulses. To allow contacts to settle before the contact level is deemed reliable and acted upon, many samples of the contact state can be taken in digital systems at a low rate and inspected for a steady sequence. A Schmitt trigger or an SR flip-flop (latch) can be used to filter out signals that bounce in SPDT switch contacts. Each of these techniques
The term "debouncing" refers to each of these techniques.
Under the manual piano keys of the Hammond organ, several wires are squeezed together. Hammond switching is the process of the switches' bouncing and asynchronous closing. There are click and compositions that highlight and utilise this feature. This sound effect is switchable on several electronic organs.
Arcs and quenching
When the amount of power being switched is high enough, the flow of electrons across the opening switch contacts is enough to ionize the air molecules across the little gap between the contacts as the switch is opened, generating a gas plasma, also known as an electric arc. Despite the switch contacts' gradually rising separation distance, the plasma's low resistance allows it to maintain power flow. The metal surfaces of the switch contacts can be eroded by the plasma's extreme heat. Arc suppression techniques are needed because electric current arcing significantly degrades the contacts and generates a lot of electromagnetic interference (EMI).
An arc can also form as the switch is closed and the contacts get close if the voltage is high enough. An arc emerges when the breakdown voltage of the air between the contacts is exceeded, and it persists until the switch is fully closed and the switch surfaces make contact.
In either case, using a quick-moving switch mechanism—typically a spring-operated tipping-point mechanism to ensure quick motion of switch contacts—is the standard method for reducing arc formation and preventing contact damage. This is true regardless of how quickly the switch control is used by the user. When a spring reaches a tipping point due to movement of the switch control lever, the contacts abruptly open.
The contacts abruptly snap open or closed as the spring tension is released as the switch control lever is moved, applying stress to a spring until a tipping point is achieved.
Other techniques are employed to reduce or avoid arc production as the amount of power being switched grows. A heated plasma will rise as a result of convection air currents. The arc can be put out by placing a series of non-conductive blades over the switch contacts. As the arc rises, it lengthens as ridges form in the spaces between the blades, eventually becoming too lengthy to maintain and going out.
In order to swiftly put out the arc, a puffer can be employed to blow a sudden, high-velocity burst of gas across the switch contacts.
To more quickly put out the arc, really big switches frequently have switch contacts encircled by something other than air. The switch contacts, for instance, might function while submerged in sulfur hexafluoride, mineral oil, or a vacuum.
It is more difficult to sustain an arc on opening when the current in an AC power service periodically crosses zero. When utilized in DC circuits, manufacturers may rate switches with lower voltage or current ratings.
Power switching
The transitional condition of the switch as well as its capacity to resist continuous operating currents must be taken into account when a switch is designed to switch considerable power. A switch's resistance is almost zero when it is in the on position, and very little power is lost in the contacts. In contrast, a switch's resistance is extremely high when it is in the off position, and even less power is lost in the contacts. However, when the switch is flipped, the resistance must pass through a condition where the switch briefly loses a quarter of the load's rated power (or worse if the load is not fully resistive).
Inductive loads
A spark will jump across the opening contacts when a very inductive load, such as an electric motor, is turned off since the current cannot drop instantly to zero. Inductive load switches must be rated to handle these scenarios. If the spark isn't put out, it will result in electromagnetic interference; however, putting a resistor and capacitor in series will put out the spark.
Incandescent loads
An incandescent lamp produces a significant inrush current that is roughly ten times the steady-state current when it is first turned on. As the filament heats up, the resistance increases and the current reduces to a steady-state value. An incandescent light load switch can handle this inrush current.
Wetting current
The bare minimal amount of current that must pass through a mechanical switch during operation in order to remove any oxidation layer that may have built up on the switch contacts is known as the wetting current. [10] High humidity locations frequently experience the layer of oxidation. A critical component of designing systems that use fragile switches with low contact pressure as sensor inputs is providing an adequate amount of wetting current. If you don't do this, contact oxidation may cause switches to remain electrically "open."
Actuator
The actuator, which can be any sort of mechanical linkage, a toggle or dolly, a rocker, a push-button, or other moving component, applies the operating force to the contacts (see photo).
Biased switches
Once flipped, a switch often stays in that position. When an operator releases it, a biased switch has a mechanism that forces it into a different position. A biased switch is a momentary push-button switch.
The most typical kind is a normally-open (NO) switch, sometimes known as a "push-to-make" switch, which makes contact when the button is pressed and disengages when it is released. For instance, each key on a computer keyboard functions as a "push-to-make" switch that is typically open. As opposed to this, a "push-to-break" (or normally-closed, or NC) switch makes contact when the button is depressed and breaks contact when it is pressed. An electromagnet-held door release button is an illustration of a push-to-break switch. A switch that is held open when the door is closed operates the internal lamp of a domestic refrigerator.
Rotary switch
When using a rotary switch, the operational handle must be rotated through at least two positions. The switch may have one or more momentary positions that need to be held by the user since they are biased by a spring. Other positions might feature a detent that keeps them in place after being released. In order to regulate various circuits, a rotary switch may have many levels, or "decks."
A contact arm or "spoke" that extends from the surface of a spindle or "rotor" like a cam constitutes one type of rotary switch. Each terminal acts as a contact for the "spoke" that allows any one of a variety of different electrical circuits to be connected to the rotor. These terminals are placed in a circle around the rotor. Each layer of the switch, which corresponds to one pole, enables the usage of many poles. Such a switch typically features a detent mechanism to prevent it from stalling in an intermediate position and instead "clicks" from one active position to another. In comparison to more basic switches, a rotary switch has more pole and throw capabilities.
Other variants control numerous separate groups of contacts using a cam mechanism.
Up to the early 1970s, rotary switches were employed for a variety of tasks, including band selection on multi-band radios, range selection on electrical metering equipment, and channel selection on television receivers. Rotary switches are used in industry to operate measurement devices, switchgear, or control circuits. To transfer hardwired control signals from the local manual controls in the cab to the outputs of the remote control receiver, for instance, a radio-controlled overhead crane might feature a sizable multi-circuit rotary switch.
Toggle switch
Electrical switches that are manually operated by a mechanical lever, grip, or rocking mechanism are referred to as toggle switches or tumbler switches.
Toggle switches come in a wide variety of shapes and sizes and are employed in a wide range of applications. Many are built to control high currents of electricity or main voltages, or to simultaneously activate many sets of electrical contacts.
The term "toggle" refers to a particular mechanism or joint that consists of two arms that are nearly parallel to one another and are joined by a pivot like an elbow.
However, whether or not a switch technically has a toggle mechanism, the term "toggle switch" refers to a switch with a short handle and a positive snap-action. A switch that produces a distinct click is referred to as a "positive on-off switch" in a similar manner. [11] Using this type of switch to turn on or off lights or other electrical devices is fairly popular. To avoid banned combinations, multiple toggle switches may be mechanically interconnected.
In some settings, notably those involving computing, the term "toggle switch" or "toggling" refers to a mechanical or software switch that, independent of its physical design, alternates between two states each time it is triggered. For instance, pushing the computer's caps lock key once causes all letters to be generated in capital letters; pressing it again causes all letters to be formed in lowercase.
Special types
Any sort of mechanical stimulus, such as vibration (the trembler switch), tilt, air pressure, fluid level, the turning of a key (the key switch), linear or rotational movement (the limit switch or microswitch), or the presence of a magnetic field, can cause a switch to react (the reed switch). Numerous switches are activated automatically when an ambient state changes or while machinery is in motion. For instance, limit switches are used in machine machines to interlock operation with appropriate tool positioning. A sail switch in HVAC systems makes ensuring there is enough airflow in a duct. Fluid pressure causes pressure switches to react.
Mercury tilt switch
A drop of mercury is placed within a glass bulb that has two or more contacts to create the mercury switch. When the bulb is tilted to cause the mercury to roll on to the two contacts, the mercury is connected to them through the glass.
This sort of switch operates significantly better than a ball tilt switch because the liquid metal connection is impervious to dust, debris, and oxidation, wets the contacts to ensure a connection with very low resistance and minimal bounce, and is not impacted by movement or vibration. These can be employed for precise tasks.
Because the entire device is sealed, it can also be utilized in situations where arcing is hazardous, like when explosive vapour is present.
Knife switch
Knife switches are made out of a permanent contact, an insulating handle, and a flat metal blade that is hinged at one end. Current flows via the blade and hinged pivot when the switch is closed, as well as through the fixed contact. Typically, these switches are not encased. Depending on the application, the knives and contacts are often made of brass, steel, or copper. Fixed contacts could have a spring backing them up. One handle can control multiple parallel blades simultaneously. The components can either be directly fastened to an insulated switch board in a large assembly or installed on an insulating base with wiring terminals.
The switch is only used in situations where people cannot accidentally come into contact with it or where the voltage is low enough to not pose a threat because the electrical contacts are exposed.
Knife switches come in a variety of sizes, from tiny switches to big devices that can handle thousands of amps. Gang-operated switches are used in electrical transmission and distribution in circuits with the greatest voltages.
The slow opening speed and the operator's proximity to exposed live parts are drawbacks of the knife switch. In the distribution of industrial power, isolation of circuits is accomplished using safety disconnect switches with metal casing. When the arc is being quickly extinguished, spring-loaded auxiliary blades may be installed. These blades temporarily carry the whole current during opening.
Footswitch
A sturdy switch that is activated by foot pressure is a footswitch. A machine tool that allows the operator to manage the workpiece with both hands free is an example of usage. Foot switches are also used as the controls for an electric guitarist's effects pedals and amplifier.
Reversing switch
A DPDT switch has six connections, however some varieties are internally wired specifically for polarity reversal because polarity reversal is a highly typical application for DPDT switches. Instead of having six terminals, these crossover switches only have four. The terminals have two inputs and two outputs each. The 4-way switch chooses between normal or reversed polarity when it is attached to a battery or other DC source. In a multiway switching system, these switches can also be utilized as intermediate switches to control lamps with more than two switches.
Light switches
Light switches are fitted in building wiring at practical positions to control lighting and sporadically other circuits. Multiway switching control of a lamp can be obtained by using multiple-pole switches from two or more locations, such as the ends of a hallway or stairs. For convenience, a wireless light switch enables remote control of lamps. Some lamps also have a touch switch that, when touched anywhere, electronically controls the bulb. To prevent illegal use, a variety of vandal-resistant switches are utilized in public facilities.
Slide switches
Using a slider that glides from the open (off) position to the closed (on) position, slide switches are mechanical switches.
Electronic switches
An electrically controlled switch is a relay. Other operating principles are also utilized, however electromagnets are frequently used in relays to mechanically activate a switching mechanism. Without any moving parts, solid-state relays manage power circuits by switching between semiconductor components, frequently a silicon-controlled triac or rectifier.
The analogue switch, which functions similarly to an electromechanical relay but with a few advantages and a few disadvantages, uses two MOSFET transistors in a transmission gate configuration as a switch.
In a switching voltage regulator, such as a power supply unit, the power transistor(s) are utilized as a switch to alternately allow and prevent electricity from flowing.
Many refer to a range of devices that conceptually connect or disconnect signals and communication pathways between electrical devices as "switches" using metonymy, similar to how mechanical switches connect and disconnect paths for electrons to travel between two conductors. Early telephone systems connected callers via an automatic Strowger switch; modern telephone exchanges have one or more crossbar switches.
Since the introduction of digital logic in the 1950s, the term switch has come to refer to a wide range of digital active devices, including transistors, logic gates, and even computers, network switches, whose purpose is to connect various ports in a computer network. These devices can switch between two logic levels or connect different signal lines. The metal-oxide semiconductor field-effect transistor is the most often utilized electronic switch in digital circuits (MOSFET).
A network that is circuit switched and offers dedicated circuits for communication between end nodes is referred to as being "switched" in the context of telecommunications networks. An example of this is the public switched telephone network. All of these uses have one thing in common: they all refer to things that have a binary state that can be either on or off, closed or open, connected or unconnected.
1
Switch
A switch is a device used in electrical engineering that has the ability to connect or disconnect a circuit's conducting line, halting the flow of electricity, or rerouting it to another conductor. An electromechanical switch, which has one or more sets of moveable electrical contacts coupled to external circuits, is the most popular type of switch. Current can flow between two contacts when they are touching, but it cannot when the contacts are apart.
The contacts on switches can work simultaneously, sequentially, or alternately, and they can have many sets of contacts that are all operated by the same knob or actuator. A switch can sense the location of a machine part, liquid level, pressure, or temperature, like a thermostat, or it can be manually activated, like a light switch or a keyboard button. Toggle switches, rotary switches, mercury switches, push-button switches, reversing switches, relays, and circuit breakers are only a few examples of the many specialized types.
Lighting control is a frequent application in which several switches may be linked into a single circuit to provide practical control of light fixtures. To avoid destructive arcing when they are opened, switches in high-powered circuits need to be specially built.
Description
A manually operated electromechanical switch having one or more sets of electrical contacts connected to external circuits is the most common type of switch. There are two possible states for each set of contacts: "closed," which means the contacts are in contact and electricity can flow between them, or "open," which means the contacts are apart and the switch is not conducting. There are numerous types of actions that can be used, but often, a "alternative action" (flipping the switch for continuous "on" or "off") or "momentary" (pushing for "on" and releasing for "off") type mechanism is used to switch between these two states (open or closed).
A switch can be directly operated by a person to regulate the flow of power in a circuit, such as a light switch, or to send a control signal to a system, like a computer keyboard button. Automatically operated switches can be used to regulate machine motions, such as to signal when a garage door has fully opened or when a machine tool is ready to accept a new piece of work. Switches can act as sensors in a process and be used to automatically control a system by being activated by process variables like pressure, temperature, flow, current, voltage, and force.
When closed, an ideal switch would have no voltage drop and no voltage or current rating restrictions. When changing states, there would be no rise time or fall time, and it would do it without "bouncing" between the on and off positions.
Practical switches fall short of this ideal because of contact resistance, constraints on the current and voltage they can handle, finite switching times, and other issues caused by roughness and oxide layers. The ideal switch is frequently employed in circuit analysis because it makes the system of equations to be solved incredibly simple. However, this can result in a less precise solution. In order to build large switch networks, such as those used in telephone exchanges, the consequences of non-ideal features must be treated theoretically.
Contacts
The simplest type of switch comprises two contacts that are linked to an external circuit and touch to complete (create) the circuit and separate to open (break) the circuit. The contacts are often made of metal. Because the majority of metals develop insulating oxides that would prohibit the switch from functioning, the contact material is chosen for its resistance to corrosion. Additionally, contact materials are selected for their electrical conductivity, mechanical strength, hardness (resistance to abrasive wear), affordability, and low toxicity. The contact resistance and wetness current of a mechanical switch are determined by the growth of oxide layers at the contact surface, surface roughness, and contact pressure.
Noble metals are occasionally used to plate connections because of their good conductivity and corrosion resistance. They might be made to rub against one another to remove any contaminants. Occasionally, nonmetallic conductors like conductive polymers are utilized. For a specific switch design, a minimum wetting current may be specified to avoid the growth of insulating oxides.
Contact terminology
Switches are categorized in electronics based on how their contacts are set up. When current can move from one contact to the other, two contacts are said to be "closed." When an insulating air gap separates the contacts, they are termed to be "open," and at normal voltages, no current can pass between them. Additionally, the words "create" for contact closure and "break" for contact opening are frequently used.
Switch contact variants are frequently referred to by the names pole and throw. The number of electrically independent switches that are each under the direction of a single physical actuator are referred to as "poles." A "2-pole" switch, for instance, has two different parallel sets of contacts that open and close simultaneously using the same mechanism. The number of "throws" refers to how many other wire path options, except "open," the switch can select for each pole. One pair of contacts on a single-throw switch can be either closed or open. A contact on a triple-throw switch can be linked to any one of three other contacts, while a contact on a double-throw switch can be connected to any of two other contacts.
A push-button switch, for example, has contacts that are either normally open (abbreviated "n.o." or "no") until the switch is operated to shut them, or normally closed ("n.c." or "nc") until the switch action opens them. Changeover switches and double-throw switches are terms used to describe switches containing both sorts of contacts. These can either be "break-before-make" (BBM or non-shorting) or "make-before-break" (MBB or shorting), which temporarily connects one circuit before closing the other.
The abbreviations "single-pole, single-throw" (SPST) and "single-pole, double-throw" (SPDT), which connect either of two terminals to the common terminal, are derived from these words and are used to refer to the many switch types used in the electronics industry. Names used in electrical power wiring (i.e., wiring of homes and buildings by electricians) typically end in "-way," but the terminologies used range between British English and American English (i.e., the terms two way and three way are used with different meanings).
A number (e.g., 3PST, SP4T, etc.) or, in some situations, the letter "T" (for "triple") or "Q" can be used to designate switches with more poles or throws (for "quadruple"). To avoid misunderstanding, the terms SPST, SPDT, and intermediate will be used throughout the remainder of this paper.
Contact bounce
Mechanical switches and relays frequently experience contact bounce (also known as chatter), which is an issue brought on by electrical contact resistance (ECR) occurrences at interfaces. Typically, springy metals are used to make switch and relay contacts. The momentum and elasticity of the contacts cause them to bounce apart once or more times before coming into steady contact when they come into touch. Instead of a smooth transition from zero to full current, the outcome is a rapidly pulsed electric current. In power circuits, the effect is typically unimportant, but it can cause issues in some analogue and logic circuits that react quickly enough to mistake the on/off pulses for a data stream.
Chatter can be prevented in the design of micro-contacts by reducing the production of passivated layers on metallic surfaces and managing surface structure (surface roughness).
Mercury-wetted contacts can be used to eliminate the effects of contact bounce, however they are no longer often used due to the risks associated with mercury. Alternately, contact circuit voltages can be low-pass filtered to minimize or completely get rid of repeated pulses. To allow contacts to settle before the contact level is deemed reliable and acted upon, many samples of the contact state can be taken in digital systems at a low rate and inspected for a steady sequence. A Schmitt trigger or an SR flip-flop (latch) can be used to filter out signals that bounce in SPDT switch contacts. Each of these techniques
The term "debouncing" refers to each of these techniques.
Under the manual piano keys of the Hammond organ, several wires are squeezed together. Hammond switching is the process of the switches' bouncing and asynchronous closing. There are click and compositions that highlight and utilise this feature. This sound effect is switchable on several electronic organs.
Arcs and quenching
When the amount of power being switched is high enough, the flow of electrons across the opening switch contacts is enough to ionize the air molecules across the little gap between the contacts as the switch is opened, generating a gas plasma, also known as an electric arc. Despite the switch contacts' gradually rising separation distance, the plasma's low resistance allows it to maintain power flow. The metal surfaces of the switch contacts can be eroded by the plasma's extreme heat. Arc suppression techniques are needed because electric current arcing significantly degrades the contacts and generates a lot of electromagnetic interference (EMI).
An arc can also form as the switch is closed and the contacts get close if the voltage is high enough. An arc emerges when the breakdown voltage of the air between the contacts is exceeded, and it persists until the switch is fully closed and the switch surfaces make contact.
In either case, using a quick-moving switch mechanism—typically a spring-operated tipping-point mechanism to ensure quick motion of switch contacts—is the standard method for reducing arc formation and preventing contact damage. This is true regardless of how quickly the switch control is used by the user. When a spring reaches a tipping point due to movement of the switch control lever, the contacts abruptly open.
The contacts abruptly snap open or closed as the spring tension is released as the switch control lever is moved, applying stress to a spring until a tipping point is achieved.
Other techniques are employed to reduce or avoid arc production as the amount of power being switched grows. A heated plasma will rise as a result of convection air currents. The arc can be put out by placing a series of non-conductive blades over the switch contacts. As the arc rises, it lengthens as ridges form in the spaces between the blades, eventually becoming too lengthy to maintain and going out.
In order to swiftly put out the arc, a puffer can be employed to blow a sudden, high-velocity burst of gas across the switch contacts.
To more quickly put out the arc, really big switches frequently have switch contacts encircled by something other than air. The switch contacts, for instance, might function while submerged in sulfur hexafluoride, mineral oil, or a vacuum.
It is more difficult to sustain an arc on opening when the current in an AC power service periodically crosses zero. When utilized in DC circuits, manufacturers may rate switches with lower voltage or current ratings.
Power switching
The transitional condition of the switch as well as its capacity to resist continuous operating currents must be taken into account when a switch is designed to switch considerable power. A switch's resistance is almost zero when it is in the on position, and very little power is lost in the contacts. In contrast, a switch's resistance is extremely high when it is in the off position, and even less power is lost in the contacts. However, when the switch is flipped, the resistance must pass through a condition where the switch briefly loses a quarter of the load's rated power (or worse if the load is not fully resistive).
Inductive loads
A spark will jump across the opening contacts when a very inductive load, such as an electric motor, is turned off since the current cannot drop instantly to zero. Inductive load switches must be rated to handle these scenarios. If the spark isn't put out, it will result in electromagnetic interference; however, putting a resistor and capacitor in series will put out the spark.
Incandescent loads
An incandescent lamp produces a significant inrush current that is roughly ten times the steady-state current when it is first turned on. As the filament heats up, the resistance increases and the current reduces to a steady-state value. An incandescent light load switch can handle this inrush current.
Wetting current
The bare minimal amount of current that must pass through a mechanical switch during operation in order to remove any oxidation layer that may have built up on the switch contacts is known as the wetting current. [10] High humidity locations frequently experience the layer of oxidation. A critical component of designing systems that use fragile switches with low contact pressure as sensor inputs is providing an adequate amount of wetting current. If you don't do this, contact oxidation may cause switches to remain electrically "open."
Actuator
The actuator, which can be any sort of mechanical linkage, a toggle or dolly, a rocker, a push-button, or other moving component, applies the operating force to the contacts (see photo).
Biased switches
Once flipped, a switch often stays in that position. When an operator releases it, a biased switch has a mechanism that forces it into a different position. A biased switch is a momentary push-button switch.
The most typical kind is a normally-open (NO) switch, sometimes known as a "push-to-make" switch, which makes contact when the button is pressed and disengages when it is released. For instance, each key on a computer keyboard functions as a "push-to-make" switch that is typically open. As opposed to this, a "push-to-break" (or normally-closed, or NC) switch makes contact when the button is depressed and breaks contact when it is pressed. An electromagnet-held door release button is an illustration of a push-to-break switch. A switch that is held open when the door is closed operates the internal lamp of a domestic refrigerator.
Rotary switch
When using a rotary switch, the operational handle must be rotated through at least two positions. The switch may have one or more momentary positions that need to be held by the user since they are biased by a spring. Other positions might feature a detent that keeps them in place after being released. In order to regulate various circuits, a rotary switch may have many levels, or "decks."
A contact arm or "spoke" that extends from the surface of a spindle or "rotor" like a cam constitutes one type of rotary switch. Each terminal acts as a contact for the "spoke" that allows any one of a variety of different electrical circuits to be connected to the rotor. These terminals are placed in a circle around the rotor. Each layer of the switch, which corresponds to one pole, enables the usage of many poles. Such a switch typically features a detent mechanism to prevent it from stalling in an intermediate position and instead "clicks" from one active position to another. In comparison to more basic switches, a rotary switch has more pole and throw capabilities.
Other variants control numerous separate groups of contacts using a cam mechanism.
Up to the early 1970s, rotary switches were employed for a variety of tasks, including band selection on multi-band radios, range selection on electrical metering equipment, and channel selection on television receivers. Rotary switches are used in industry to operate measurement devices, switchgear, or control circuits. To transfer hardwired control signals from the local manual controls in the cab to the outputs of the remote control receiver, for instance, a radio-controlled overhead crane might feature a sizable multi-circuit rotary switch.
Toggle switch
Electrical switches that are manually operated by a mechanical lever, grip, or rocking mechanism are referred to as toggle switches or tumbler switches.
Toggle switches come in a wide variety of shapes and sizes and are employed in a wide range of applications. Many are built to control high currents of electricity or main voltages, or to simultaneously activate many sets of electrical contacts.
The term "toggle" refers to a particular mechanism or joint that consists of two arms that are nearly parallel to one another and are joined by a pivot like an elbow.
However, whether or not a switch technically has a toggle mechanism, the term "toggle switch" refers to a switch with a short handle and a positive snap-action. A switch that produces a distinct click is referred to as a "positive on-off switch" in a similar manner. [11] Using this type of switch to turn on or off lights or other electrical devices is fairly popular. To avoid banned combinations, multiple toggle switches may be mechanically interconnected.
In some settings, notably those involving computing, the term "toggle switch" or "toggling" refers to a mechanical or software switch that, independent of its physical design, alternates between two states each time it is triggered. For instance, pushing the computer's caps lock key once causes all letters to be generated in capital letters; pressing it again causes all letters to be formed in lowercase.
Special types
Any sort of mechanical stimulus, such as vibration (the trembler switch), tilt, air pressure, fluid level, the turning of a key (the key switch), linear or rotational movement (the limit switch or microswitch), or the presence of a magnetic field, can cause a switch to react (the reed switch). Numerous switches are activated automatically when an ambient state changes or while machinery is in motion. For instance, limit switches are used in machine machines to interlock operation with appropriate tool positioning. A sail switch in HVAC systems makes ensuring there is enough airflow in a duct. Fluid pressure causes pressure switches to react.
Mercury tilt switch
A drop of mercury is placed within a glass bulb that has two or more contacts to create the mercury switch. When the bulb is tilted to cause the mercury to roll on to the two contacts, the mercury is connected to them through the glass.
This sort of switch operates significantly better than a ball tilt switch because the liquid metal connection is impervious to dust, debris, and oxidation, wets the contacts to ensure a connection with very low resistance and minimal bounce, and is not impacted by movement or vibration. These can be employed for precise tasks.
Because the entire device is sealed, it can also be utilized in situations where arcing is hazardous, like when explosive vapour is present.
Knife switch
Knife switches are made out of a permanent contact, an insulating handle, and a flat metal blade that is hinged at one end. Current flows via the blade and hinged pivot when the switch is closed, as well as through the fixed contact. Typically, these switches are not encased. Depending on the application, the knives and contacts are often made of brass, steel, or copper. Fixed contacts could have a spring backing them up. One handle can control multiple parallel blades simultaneously. The components can either be directly fastened to an insulated switch board in a large assembly or installed on an insulating base with wiring terminals.
The switch is only used in situations where people cannot accidentally come into contact with it or where the voltage is low enough to not pose a threat because the electrical contacts are exposed.
Knife switches come in a variety of sizes, from tiny switches to big devices that can handle thousands of amps. Gang-operated switches are used in electrical transmission and distribution in circuits with the greatest voltages.
The slow opening speed and the operator's proximity to exposed live parts are drawbacks of the knife switch. In the distribution of industrial power, isolation of circuits is accomplished using safety disconnect switches with metal casing. When the arc is being quickly extinguished, spring-loaded auxiliary blades may be installed. These blades temporarily carry the whole current during opening.
Footswitch
A sturdy switch that is activated by foot pressure is a footswitch. A machine tool that allows the operator to manage the workpiece with both hands free is an example of usage. Foot switches are also used as the controls for an electric guitarist's effects pedals and amplifier.
Reversing switch
A DPDT switch has six connections, however some varieties are internally wired specifically for polarity reversal because polarity reversal is a highly typical application for DPDT switches. Instead of having six terminals, these crossover switches only have four. The terminals have two inputs and two outputs each. The 4-way switch chooses between normal or reversed polarity when it is attached to a battery or other DC source. In a multiway switching system, these switches can also be utilized as intermediate switches to control lamps with more than two switches.
Light switches
Light switches are fitted in building wiring at practical positions to control lighting and sporadically other circuits. Multiway switching control of a lamp can be obtained by using multiple-pole switches from two or more locations, such as the ends of a hallway or stairs. For convenience, a wireless light switch enables remote control of lamps. Some lamps also have a touch switch that, when touched anywhere, electronically controls the bulb. To prevent illegal use, a variety of vandal-resistant switches are utilized in public facilities.
Slide switches
Using a slider that glides from the open (off) position to the closed (on) position, slide switches are mechanical switches.
Electronic switches
An electrically controlled switch is a relay. Other operating principles are also utilized, however electromagnets are frequently used in relays to mechanically activate a switching mechanism. Without any moving parts, solid-state relays manage power circuits by switching between semiconductor components, frequently a silicon-controlled triac or rectifier.
The analogue switch, which functions similarly to an electromechanical relay but with a few advantages and a few disadvantages, uses two MOSFET transistors in a transmission gate configuration as a switch.
In a switching voltage regulator, such as a power supply unit, the power transistor(s) are utilized as a switch to alternately allow and prevent electricity from flowing.
Many refer to a range of devices that conceptually connect or disconnect signals and communication pathways between electrical devices as "switches" using metonymy, similar to how mechanical switches connect and disconnect paths for electrons to travel between two conductors. Early telephone systems connected callers via an automatic Strowger switch; modern telephone exchanges have one or more crossbar switches.
Since the introduction of digital logic in the 1950s, the term switch has come to refer to a wide range of digital active devices, including transistors, logic gates, and even computers, network switches, whose purpose is to connect various ports in a computer network. These devices can switch between two logic levels or connect different signal lines. The metal-oxide semiconductor field-effect transistor is the most often utilized electronic switch in digital circuits (MOSFET).
A network that is circuit switched and offers dedicated circuits for communication between end nodes is referred to as being "switched" in the context of telecommunications networks. An example of this is the public switched telephone network. All of these uses have one thing in common: they all refer to things that have a binary state that can be either on or off, closed or open, connected or unconnected.
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