Product category:
Switches and Keyboards
News Release from: Schurter Input Systems | Subject: Metal Line
Edited by the Electronicstalk Editorial
Team on 07 September 2007
Key factors in switch specification
Jochen Ullmer examines important criteria to consider when selecting switches for human-machine interfaces.
Vandal-proof input systems have now spread into a huge range of applications These operating elements are chosen for their robust nature and, increasingly, also for design reasons
This article was originally published on Electronicstalk on 10 Aug 2006 at 8.00am (UK)
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A new catalogue provides an overview of robust and vandal-proof Metal Line input systems.
Metallic switches snap into place
Metallic switches with snap in technology enable quick and efficient assembly in buildings, controllers or equipment with limited or no access from the rear.
The range of products for such input systems is just as diverse as the application areas in which they are deployed.
There are piezo switches, metal switches with varying strokes, metal switches with tactile feedback and switches based on sensors such as capacitive technology.
Within this classification, a combination of the various technologies is also possible.
Further reading
Illuminated switches get the blues
Metal Line switches are now available with blue illumination in addition to the existing yellow, red and/or green options.
Piezo switches are sealed to the highest levels
Piezo switches sealed to IP69K can be used in equipment designed for areas that are regularly disinfected or cleaned using high-pressure cleaners.
Latching function eases switch use
The MSM LA switch provides a user-friendly actuating function and also prevents inadvertent switching, for example by objects leaning on the switch.
A piezo switch may be additionally equipped with an element for tactile feedback, for example.
In order to make an appropriate choice when it comes to input or operating systems, all important ambient factors associated with the particular device must be taken into account.
Important factors include location, climatic requirements as well as the function to be triggered.
When it comes to considering the location issue, a differentiation must be made between devices that are used exclusively inside buildings, those that are located outside but with a covering and those that are outside with total exposure to the elements.
Devices that are located outside with total exposure need, in most cases, to be able to withstand snow and ice and thus minus temperatures.
Under such ambient conditions it is possible for switches with stroke (or travel) to temporarily fail.
Water may penetrate into the space between the moving parts.
When minus temperatures set in, these moving parts then freeze and the actuator can no longer be depressed for closing the contact.
Piezo switches with completely sealed surfaces lend themselves particularly well to meeting the demands of devices located outside with no protective covering.
When it comes to protecting the device against dust and liquids, the components are specified according to IP protection classes.
Piezo switches fulfil a protection class of at least IP67.
Metal switches with stroke or tactility on the other hand are designed with varying protection classes of between IP40 and IP67.
In the case of metal switches, a differentiation is made between the IP protection at the mechanical level and that at the electrical contact level.
This means that the electrical contact level might have a protection class of IP67, for example, whereas the mechanical level demonstrates a protection class of IP40.
This differentiation is represented with the different characteristic values in the product documentation and in the relevant selector charts on the Schurter website.
The differentiation is important when it comes to considering the mounting position or possible ambient impurities.
When mounting on horizontal or slightly inclined surfaces, a hazard is posed, for example, by unintentionally spilled liquids entering the inside of the switch.
If a switch is used which has the combination of protection classes described above, the functionality of the switch is initially still guaranteed after the liquid has penetrated it.
However, if the liquid is a sugar-containing substance such as lemonade or sweetened coffee, the function will become increasingly impaired.
The liquid evaporates and the sugar which remains leads to the switch becoming stiff, possibly leading to jamming of the actuator.
In order to avoid such impairment, a vertical mounting position should be chosen insofaras the device design permits this.
Alternatively, the use of a piezo switch is recommended here, too.
The function of the switch is also important when it comes to selecting its type.
Frequently, the switches are arranged next to a display and the menu navigation is controlled via the display.
An additional possibility for operator guidance is to provide the switch surface with an inscription, either using text or appropriate symbols.
Each time the switch is activated, the device operator should receive feedback that the activation of the switch has been acknowledged by the machine.
This feedback may be acoustic, haptic or optical.
Alternatively, it may be discernible from the fact that the relevant function is triggered on the device.
Optical feedback is possible by integrated illumination on the switch or by means of an appropriate display on the monitor.
In the case of self-service terminals, the information or help keys should always be provided with a switch that has a high degree of tactile feedback.
As the operator only usually activates these keys in an emergency, clear feedback that the key signal has been carried out is necessary in such a situation.
The stimuli perceived via the sense of touch are most rapidly discernible by the operator.
The PM Abacus pay machine system from Designa is a good illustration of these criteria in operation.
The switches used in this unit are produced from high-quality stainless steel and are very flat at the front of the device.
This provides potential vandals with very little contact surface.
An O-ring between the switch housing and the front of the device protects the inside of the device from humidity.
The vertical mounting position of the switch and the additional overhead covering prevents liquids from penetrating into the mechanical part of the switch.
The information key on the pay machines is provided with a switch that has high tactility.
Robust metal switches are used across the globe in various application areas, including in ticket terminals and gas stations, at information stands, in access control facilities, sanitary facilities, on public transport, in construction machinery and on control panels for industrial facilities.
The application areas of the metal switches are just as diverse as the technical and design possibilities provided by the switches from the Schurter Metal Line range. Request a free brochure from Schurter Input Systems ...
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