Switches

 

Overview of switches

Switches now perform such crucial roles in so many manufacturing processes and technological devices that if they were to collectively malfunction or disappear, essential services that society takes for granted - such as clean water and regular energy supply – would terminate immediately. 

Their essential functions - to enable or interrupt the flow of electricity around an electrical circuit, or literally “switch” the trajectory of the current from one conductor to another – has been exploited in countless machines and technological devices.

One sophisticated example is a piece of hardware called the KVM switch (Keyboard, Video, Mouse), which allows people to operate several computers from one or more keyboard, video monitor or mouse (very useful in datacentres or for adding a full-size keyboard and mouse to small mobile gadgets like laptops, tablets and PDAs).

From computer keyboards responding to human touch to send electrical signals to the computer, to the control of garage doors (automatically sensing when the door is fully open), to the thermostat regulating the temperature in a fridge – all these  inventions and many more are governed by the imaginative and skilful deployment of a raft of different switches.

 

History of the switch

With the advent of electric power, nineteenth century scientists and inventors were able to devise various techniques to stop and start the flow of current around a circuit.

An expression of high Victorian progress, the first light switch was produced by English inventor John Jeffrey Holmes in 1884 (dimmer switches were invented 6 years later by Granville Woods, but it wasn’t until 1905 that the toggle switch for lighting circuits was devised). Holmes’ “quick break technology”, which breaks or closes the circuit virtually instantly and prevents damage to the switch’s contacts caused by arcing, is still in use today - although in most modern buildings the toggle switch has largely given way to the rocker switch.  This opens and breaks the circuit by means of a ‘rocking horse’ motion – when one side of the switch is depressed, the other side rises.

 

Important technical elements

To simplify equations in their theoretical circuit analyses, engineers and designers often use the concept of the “ideal switch”, which displays no drop in voltage upon closing, operates instantaneously with no rise and fall time lags upon opening or closing, and has no limits on its current rating or voltage.

But in the real world the ideal switch simply doesn’t exist. Real switches have measurable switching times, they have resistances, and they have limits on the voltages and currents they can handle. Ideal switches can, then, lead to inaccurate solutions in the real world if the properties of real materials are ignored. Designers and manufacturers of switches always include the effects of non-ideal properties in their theoretical models of large networks of switches (like telephone exchanges) so that inaccuracies are not multiplied.

 

Overview of the different switch types from a manufacturing perspective

Dimmer Switch

Popular in domestic settings, the dimmer switch can alter the intensity of the lightbulb by means of using a variable resistor. Recent developments have seen the dimmer progress from analogue electronics to digital systems, where a microprocessor offers greater flexibility for professionals – such as lighting designers – who require a fine degree of control. Read More here

Toggle Switch

Manually actuated by a handle, lever or rocking mechanism, toggle switches are available in a vast array of different styles and sizes and are applied in domestic and industrial use. The “toggle” is a mechanism made up of two arms nearly in line with one another and connected via an elbow-like pivot. Any switch with a positive snap action produced by flipping a short handle can be termed a toggle switch in non-technical parlance, however. In industry, they are frequently interlocked mechanically to protect against forbidden combinations and regularly used to control high voltages or large currents. They’re also often used to achieve the simultaneous actuation of large numbers of electrical contacts. Read More here

Reed Switch

This electrical switch, invented by W. B. Ellwood in 1936 at the Bell Telephone Laboratories, consists of a hermetically sealed glass capsule containing two contacts on thin ferrous metal strips or “reeds”. The contacts remain open unless subject to a magnetic field, whereupon they close. The switch can be actuated either by bringing a magnet into proximity with it or via a coil which forms a reed relay (several reed switches can be placed within the coil). As soon as the magnetic field is removed, the switch returns to the open state. A common application is the proximity sensor on a burglar alarm, which detects the opening of a door or window. They’re also responsible for putting laptops to sleep (hibernation mode) when the lid is closed, as well as functioning as speed sensors on car gears and bicycle wheels. Read More here

Rocker Switch

Rocker switches literally “rock” when pressed to open or close electrical contacts rather than trip: as one side rises, the other side falls, just like a rocking horse. They’re frequently used in surge protectors, computer power supplies, display monitors and numerous appliances. Rocker switches can be wired into multiway switch systems, so that an upstairs light can be flipped on from the lower storey and flipped off at the top of the stairs. Read More here

Pressure Switch

Pressure switches are designed to close an electrical contact at the point at which a pre-set pressure has been reached on its input. They may be configured to close on pressure fall or rise, although some are designed to detect mechanical force such as the pressure-sensitive mats that actuate the opening of automatic doors in commercial buildings. Essentially, they contain an element (a diaphragm, piston, bellows or Bourdon tube) that distorts proportionally with applied pressure, activating the switch when the set pressure is achieved. They’re used industrially to; for example to switch off electrically-driven gas compressors when the gas pressure in the reservoir hits the desired level, or when there is no feed in the suction stage. Other uses include activating warning lights in aircraft cockpits if cabin pressure becomes critically low, or switching on dashboard warning lights in cars when engine oil pressure drops below a safe level. Read More here

Micro Switch

Micro Switches also known as “miniature snap-action switches”, these electrical switches can be actuated by means of relatively tiny physical force via a tipping-point or “over-centre” mechanism. Essentially, a small movement of the actuator button is converted into a large movement at the contacts, a process which occurs extremely rapidly. Just as rapidly, the contacts can be reversed with an equally small reversal at the actuator (a process known as “hysteresis”). As a result, micro switches (which are also highly durable and low in cost) are used to produce reliable and clean interruptions in the switched circuit.

They’re frequently used to regulate tamper switches on fire sprinkler systems, ensure the efficiency of safety and levelling switches on elevators, or operate the door interlock function on microwave ovens (they’re also responsible for detecting paper jams in photocopying machines). Read More here

Wireless switches

Wireless switches are comprised of a switching system in two sections. They use signals from a wireless transmitter to route information and thus can be attached to any convenient surface, such as a wall. The advantages of this system are manifold, but the most obvious is that they allow for less wiring than using traditional approaches. Read More here.

 

Summary

The variety of electrical switches in use today and the diversity of their applications means that modern-day life would quickly collapse if they malfunctioned, with possibly catastrophic effects.

All of today’s switches, from the simple rocker switch to the wireless switch, are rigorously tested after they’ve been through the theory and design process.