Switch Contents
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Switch Contents 1 Switch 1 1.1 Description .............................................. 1 1.2 Contacts ................................................ 2 1.2.1 Contact terminology ..................................... 2 1.2.2 Contact bounce ........................................ 3 1.2.3 Arcs and quenching ...................................... 3 1.2.4 Power switching ....................................... 3 1.2.5 Inductive loads ........................................ 4 1.2.6 Incandescent loads ...................................... 4 1.2.7 Wetting current ........................................ 4 1.3 Actuator ................................................ 4 1.3.1 Biased switches ........................................ 4 1.3.2 Rotary switch ......................................... 4 1.3.3 Toggle switch ......................................... 5 1.4 Special types .............................................. 6 1.4.1 Mercury tilt switch ...................................... 6 1.4.2 Knife switch .......................................... 6 1.4.3 Footswitch .......................................... 6 1.4.4 Reversing switch ....................................... 7 1.5 Light switches ............................................. 7 1.6 Electronic switches .......................................... 7 1.7 Other switches ............................................. 7 1.8 See also ................................................ 8 1.9 References .............................................. 8 1.10 External links ............................................. 8 2 Miniature snap-action switch 9 2.1 History ................................................. 9 2.2 Construction and operation ...................................... 9 2.3 Applications .............................................. 10 2.4 See also ................................................ 10 2.5 References ............................................... 10 2.6 External links ............................................. 10 i ii CONTENTS 3 DIP switch 12 3.1 Types ................................................. 12 3.2 Applications .............................................. 13 3.3 Notes ................................................. 13 3.4 External links ............................................. 13 4 Rotary switch 14 4.1 See also ................................................ 14 5 Limit switch 15 5.1 References ............................................... 16 6 Photoelectric sensor 17 6.1 Types ................................................. 17 6.2 Sensing modes ............................................ 17 6.2.1 Difference Between Modes .................................. 17 6.3 See also ................................................ 18 6.4 References ............................................... 18 7 Opto-isolator 19 7.1 History ................................................. 19 7.2 Operation ............................................... 19 7.3 Electric isolation ............................................ 19 7.4 Types of opto-isolators ........................................ 20 7.4.1 Resistive opto-isolators .................................... 20 7.4.2 Photodiode opto-isolators ................................... 21 7.4.3 Phototransistor opto-isolators ................................. 22 7.4.4 Bidirectional opto-isolators .................................. 22 7.5 Types of configurations ........................................ 22 7.6 Alternatives .............................................. 22 7.7 Notes ................................................. 23 7.8 References ............................................... 24 7.9 Sources ................................................ 25 7.10 External links ............................................. 26 8 Thermal cutoff 27 8.1 Thermal fuse ............................................. 27 8.2 Thermal switch ............................................ 27 8.2.1 Manual reset ......................................... 28 8.3 See also ................................................ 28 8.4 References ............................................... 28 9 Pressure switch 29 9.1 Pressure switches ........................................... 29 CONTENTS iii 9.2 Examples ............................................... 29 9.2.1 Pneumatic ........................................... 29 9.2.2 Hydraulic ........................................... 30 9.3 See also ................................................ 30 9.4 References .............................................. 30 9.5 External links ............................................. 30 10 Proximity sensor 31 10.1 Types of sensors ............................................ 31 10.2 Applications .............................................. 31 10.3 Manufacturers ............................................. 32 10.4 References ............................................... 32 10.5 Text and image sources, contributors, and licenses .......................... 33 10.5.1 Text .............................................. 33 10.5.2 Images ............................................ 34 10.5.3 Content license ........................................ 36 Chapter 1 Switch For other uses, see Switch (disambiguation). electricity can flow between them, or “open”, meaning “Toggle button” redirects here. For the GUI widget, see the contacts are separated and the switch is nonconduct- Cycle button. ing. The mechanism actuating the transition between In electrical engineering, a switch is an electrical compo- these two states (open or closed) can be either a "toggle" (flip switch for continuous “on” or “off”) or "momentary" (push-for “on” or push-for “off”) type. A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. Automatically operated switches can be used to control the motions of machines, for example, to indicate that a garage door has reached its full open position or that a machine tool is in a position to accept another work- piece. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, and force, acting as sensors in a process and used to auto- matically control a system. For example, a thermostat is a temperature-operated switch used to control a heating process. A switch that is operated by another electrical Electrical switches. Top, left to right: circuit breaker, mercury circuit is called a relay. Large switches may be remotely switch, wafer switch, DIP switch, surface mount switch, reed operated by a motor drive mechanism. Some switches are switch. Bottom, left to right: wall switch (U.S. style), miniature used to isolate electric power from a system, providing a toggle switch, in‑line switch, push-button switch, rocker switch, visible point of isolation that can be padlocked if neces- microswitch. sary to prevent accidental operation of a machine during maintenance, or to prevent electric shock. nent that can break an electrical circuit, interrupting the current or diverting it from one conductor to another.[1][2] An ideal switch would have no voltage drop when closed, The mechanism of a switch may be operated directly by and would have no limits on voltage or current rating. a human operator to control a circuit (for example, a light It would have zero rise time and fall time during state switch or a keyboard button), may be operated by a mov- changes, and would change state without “bouncing” be- ing object such as a door-operated switch, or may be op- tween on and off positions. erated by some sensing element for pressure, temperature Practical switches fall short of this ideal; they have resis- or flow. A relay is a switch that is operated by electric- tance, limits on the current and voltage they can handle, ity. Switches are made to handle a wide range of voltages finite switching time, etc. The ideal switch is often used and currents; very large switches may be used to isolate in circuit analysis as it greatly simplifies the system of high-voltage circuits in electrical substations. equations to be solved, but this can lead to a less accurate solution. Theoretical treatment of the effects of non-ideal properties is required in the design of large networks of 1.1 Description switches, as for example used in telephone exchanges. The most familiar form of switch is a manually oper- ated electromechanical device with one or more sets of electrical contacts, which are connected to external cir- cuits. Each set of contacts can be in one of two states: either “closed” meaning the contacts are touching and 1 2 CHAPTER 1. SWITCH Triple-pole single-throw (TPST or 3PST) knife switch used to short the windings of a 3‑phase wind turbine for braking pur- poses. Here the switch is shown in the open position. switch contact variations. The number of "poles" is the number of separate circuits which are controlled by a single switch. For example, a "2-pole" switch has two separate identical sets of contacts controlled by the same A toggle switch in the “on” position. switch. The number of "throws" is the number of separate wiring path choices other than “open” that the switch can adopt for each pole. A single-throw switch has one pair 1.2 Contacts of contacts that can either be closed or open. A double- throw switch has a contact that can be connected to either In the simplest case, a switch has two conductive pieces, of two other contacts, a triple-throw has a contact which often