When designing custom, rugged input solutions or sensors for industrial environments, a few key factors hardware and design engineers should pay attention to are excellent performance, quality materials and workmanship as well as simple yet sleek design and user experience to provide optimal operation even after millions of uses.
Let’s take a closer look at some of the important design factors as they apply to membrane switches, membrane sensors and touchscreen solutions for harsh environments.
The devices and their enclosures as well as sensors must go through extensive tests before a final product is developed. This includes testing material resistance to salt spray, acid, fuel, humidity, solvents, water absorbance, and other substances that can corrode or affect the performance of the material. Mechanical properties of the materials are also tested to calculate hardness, elastic moduli, and similar data. Furthermore, Linearity, Hysteresis and Repeatability (LHR) tests are carried out to determine precision of the device.
- Linearity – the extent to which the actual measured curve of a sensor departs from the ideal, theoretical curve. Linearity tells us the deviation error derived from the straightness of a set of recorded measurements when compared to a straight line.
- Hysteresis – the difference between two separate measurements taken at the same point in a cycle, the first taken during a series of increasing measurement values, and the other during a series of decreasing measurement values.
- Repeatability – the amount of change in a measured reading at the same measurement point after a defined number of cycles over the measurement range or a set of environmental limits.
Product Design and IP Ratings
Every input device, from force sensors to touchscreens, has an IP rating (International Protection Rating). This rating categorizes levels of ingress of foreign bodies (i.e. dirt, moisture) into the system and is used to define levels of sealing effectiveness of enclosures. An IP rating consists of the letters “IP” followed by two digits; the first numeral for protection against solid particles and the second numeral for protection against liquid.
The first digit can range from 0 to 6. The number “0” indicates little or no protection. The higher the number, the more protection and sealing against dust, droplets or condensation. The number “6” means that a vacuum seal is applied and the system is completely dust tight. The second digit can range from 0 to 9. A value of “9” signifies protection against high-pressure, high-temperature jet sprays, and steam-cleaning procedures. For example, an IP rating of IP65 means that the enclosure is dust tight with protection against low-pressure jets (6.3 mm) of directed water.
H+K develops various kinds of housings and enclosures for its input devices and sensors, but most commonly uses stainless steel enclosures to ensure the greatest protection from intrusion and moisture. Stainless steel is resistant to oxidation, corrosion, and chemical-resistant, making it an excellent choice in the manufacture of electrical enclosures. Different compositions of steel enclosures can change the IP rating.
GT Domed Key Technology
GT refers to a special kind of heavy-duty domed key for membrane switches with a patented process by H+K, providing matchless durability, longevity and aesthetics and additional safety forthe user interface. The proprietary polyurethane system is applied directly to polyester foils. It consists of a hardened polymer that creates a thin plastic dome over each key, with a thickness of 1.0 ± 0.5 mm, depending on key geometry. Besides the raised feel guiding the user during operation, the aesthetically pleasing design and tactile feedback, the GT technology provides self-healing properties that return the domed key to its original shape even after coming in contact with sharp objects. This material enhances the lifetime of the membrane switch and facilitates quick damage recovery.
A product life cycle gives the number of operations a product can withstand before losing functioning ability. H+K’s input devices, custom interfaces and sensors have exceptional lifespans and maintain a stable, competitive performance level over time due to their efficient design, state of the art workmanship and outstanding quality of materials used.
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Ariadna is a junior at Cornell University studying Materials Science and Engineering. She is a staff writer for The Cornell Daily Sun and a member of the Nanoscale Materials for Energy Lab.