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Some designers may consider selecting the correct switch to be a relatively simple decision. However, with the plethora of types available – even in the specialist rugged category – and the multitude of ways of deploying the switch, it is all too easy to make a less than optimal decision. Picking the wrong switch will have a negative impact on the product or system, whether it is a negative user perception or partial or complete system failure.
By working through a process of thinking about the application and what the switch is to be used for – and how it will be used – designers can arrive at the best switch for a given application, ensuring a positive user experience and long-term reliability.
A switch is a component in an electrical or electronic circuit, so a good place to start is to think about what the switch’s function in that circuit should be. Designers would normally consider what is to be switched. Is power to be routed through the switch or is it to be used for logic levels where the power rating for the switch is unimportant? If power is to be passed through the switch, then the voltage and current rating will be primary considerations. In some cases, where designers want to switch high power, a better (and safer) approach may be to use a remote relay and then use a lower power switch to operate the relay, avoiding the cost, difficulty and potential safety issues with bringing high levels of power to the front panel.
The arrangement of the switch contacts is also key to the selection process – should the switch have a single pole or two, or more? Should the contacts be normally open or closed, and should the action be momentary or latching?
Operating life is important to ensure the overall reliability of the system. Depending on the role of the switch, the requirements could be very different – a master power switch could be used relatively infrequently whereas a switch to select menu items, for example, could be used much more often and require a correspondingly longer rated life.
The type of signal to be carried may have an impact on which type of switch is selected, for example, if shielding or a particular bandwidth is required.
Switches for harsh environments
Harsh environments come in many forms, especially for switches. The environment itself is a consideration – will the switch be exposed to the elements in an outside environment, or in a well-regulated office environment? Switches to be used outside will need to be resistant to the weather and environment – this may include moisture and dust. Even in some indoor environments, such as heavy industry or food manufacturing where equipment is washed down, a sealed switch may well be a requirement. If the equipment/system is IP-rated then a switch must be chosen to meet this rating and in other situations it may still be prudent to select an IP-rated switch.
The other 'environmental' factor is the operator of the switch. It is a very different matter selecting a switch to be used on a piece of hi-fi equipment in the owner’s home to a switch in a piece of equipment to be used by the general public. In general, switches for public use will have a hard life and may even be subject to deliberate vandalism. Fortunately, vandal-proof switches are available which protect against deliberate damage. Users in harsh environments may be wearing gloves due to the environment, which is also a consideration for designers – for example, capacitive switches are useless for gloved operators, but piezoelectric switches would be a good choice as they only require pressure and not skin contact to operate.
In short, understanding the application and all possible use cases is essential to understand the environment in which the switch will be used. While weather and the operator are two possible sources of damage, other factors will apply as well. For example, a switch used on machinery may be subject to excessive and prolonged vibration and in some industrial environments aggressive chemicals could destroy plastic switches, leading to the use of stainless steel switches. In many cases, not only must the switch itself be IP-rated, but also the method of mounting (including any gasket) must ensure that the sealing level is maintained.
Other practical considerations
Space is a constant challenge in many modern applications with end users demanding ever-more functionality in an ever-decreasing form factor. As a result both the front panel space for switches as well as the space behind the panel can be limited, impacting the switches that can be chosen. For example, it may be better to avoid switching power on the front panel, instead using a smaller switch to control a remote switch (MOSFET/relay) elsewhere in the system.
Switch selection can have a significant impact on the ergonomics of the overall system and correct selection of switch features can make a front panel easy and intuitive to use, adding value to the system. For example, switches should be suitably sized for the user and the application – larger buttons may be a consideration to accommodate potential users who are mobility- or visually-impaired.
The colour of the switch can be important – red is almost universally recognised as ‘power’ or ‘stop’ while green is seen by almost everyone as meaning ‘on’. Depending on the application, coloured switches can be used to correspond to soft menu options on a display, or even to enhance the branding of a unit.
Switches are available with common legends printed on them – this saves panel space as no separate legend is required. It can also be useful if there are several versions of a product where the switch performs different functions as a common front panel design can be used, saving cost.
With LED technology becoming more commonly available, illuminated switches are now a highly popular choice. They are useful for use in reduced light conditions as well as an indicator, for example ‘Power On’. As low power LED technology is used, these have minimal impact on system efficiency and are also suitable for use in battery-powered systems. By incorporating the indicator LED into the switch body, front panel space is saved.
The final consideration is that of certification. Often mains rated switches will carry UL, CSA, ENEC or other electrical safety approvals. Another common certification is related to the material with UL94V-0 indicating that the material is self-extinguishing. The IP series of ratings are particularly valuable for switches to be used in harsh, dusty or damp environments as they guarantee various levels of ingress protection ensuring that moisture and dirt does not penetrate the switch, causing premature failure.
While, at first, selecting a switch for use in a harsh environment may seem to be a daunting prospect based on the sheer number of types, styles and options available, it need not be. Designers that are armed with a good understanding of the application and the usage environment can quickly define the requirements in terms of electrical function, reliability, sealing and the switch’s appearance to arrive at an optimum solution.
With an extensive range of push button, vandal resistant, piezo, slide, toggle and rocker switches available, Bulgin’s switch offering will meet the needs of a wide variety of applications including those found in the medical, industrial, marine and commercial sectors. The push button types are available in front and rear panel mounted versions with three profile types including prominent, domed and low profile. A comprehensive range of rugged and vandal-resistant stainless steel push button switches are also available as well as IP66, IP67 and IP68 sealed products.
About the author:
Christian Taylor is the leader of Bulgin's Engineering team, which provides expert advice and support to design engineers for bespoke connector solutions in any application. A chartered engineer with a Batchelor of Engineering (BEng) and Aerospace Manufacturing from the University of the West of England and a Master of Science (MSc) from the Manchester Metropolitan University, Taylor is adept at finding creative and inventive solutions for today's engineering challenges. Before joining Bulgin in 2015, Taylor was Project Engineer for Aker Solutions, developing products for the oil and gas sector and prior to this, he was Principal Engineer for Qualification and Test Support at Siemens plc (UK).
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