HMI solutions for extreme environments

05-07-2022 | Schurter | Connectors, Cables & Enclosures

Freezing cold, summer heat or thunderstorms - in extreme weather conditions, many input systems swiftly reach their limits. Increased protection against vandalism also plays a crucial role in using robust input systems. Also, the high demands on hygiene pose an additional requirement. Therefore, input systems used in highly specialised HMI applications under harsh environmental conditions need extensive experience in development and design.

Applications in demanding environments always need special solutions. Input systems with appropriately qualified materials guarantee maximum reliability to satisfy all requirements. These input systems are manufactured utilising state-of-the-art production technology and meet the highest industrial and medical standards.

Robust and durable for harsh environments

Touch panels have proven their importance as an interface between man and machine in many applications for years. For new developments in the industrial sector, they are the most important operating concept. For extreme requirements, robust and durable input systems are used. When selecting the appropriate touch technology and developing and designing such HMI touch panels, the application's required specifications must be considered.

Increased requirements

In addition to a visually appealing and easy-to-install design, the requirements for touch panels in industry are, above all, durability and robustness. Industrial applications demand scratch-resistant and mirror-free surfaces. They also must withstand high stresses caused by water jets, steam and dirt to maintain tightness against aggressive, harmful gases. The entire surface of the input system must be resistant to oil, solvents and aggressive chemicals and meet the IP67 protection class. In addition, flawless operation with gloves must be guaranteed.

A continuously closed front structure without soiled edges is required. This design facilitates the cleaning of the touch panels, which is of great importance in the food industry. A reflection-free surface with optimal image brilliance and sharpness is primarily required in process visualisation. All components of the input system must meet EMC conformity.

In medical technology, special challenges arise for the operating units concerning lighting options, saltwater resistance, EMC shielding, antimicrobial surfaces, and chemical resistance.

Outdoor applications require sunlight-readable touch displays with increased UV resistance and weather-resistant materials. The input systems must withstand extreme temperature changes and the influence of humidity and water. An extended temperature range of -40C to +85C is required.

Industrial applications

Capacitive PCAP touch technology is a mature technology designed to meet industrial requirements comprehensively. Capacitive multitouch film sensors are laminated optically, which is highly transparent behind printed front glasses. Glass-based sensors are bonded with special materials. The selection of hardened glasses guarantees robustness against mechanical stress. In combination with a laminated glass panel laminated on the back, vandal-proof touch panels for public applications can be realised. Special sensors have been developed for use behind 10 mm thick front glass for touch panels in hazardous areas. For use in food production, splinter-free front materials are used. In addition to PMMA, polymer composite materials are available as unbreakable front material with extreme impact resistance with IK 10 specification. Furthermore, the front glasses are laminated with a shatter-proof film for such applications.

The use of pre-qualified controller systems fully guarantees EMC conformity in accordance with the industry standard. The front glass is integrated all around through a chemical-resistant gap encapsulation. Front glasses with an antiglare surface reduce reflections and resist mechanical and chemical influences. Operating temperatures from -40C to +85C are made possible by selecting qualified materials.

Medical applications

PCAP technology is qualified for medical applications and meets water and saltwater resistance requirements, EMC immunity, glove operability, antimicrobial surfaces and chemical resistance. The display is integrated with optical bonding for optimal visualisation of the screen content.

Integrating the PCAP sensors behind a printed cover glass enables an attractive design in customised colours, various backlighting options, and an easy-to-clean, closed surface. The structure of the cover glass is optimally adapted to requirements such as antireflection, antimicrobial effect, pleasant haptics, or dirt repellency. Antimicrobial and antiviral mechanisms based on silver ion particles are coated onto the cover glass surface in a special process. This coating is stable over the entire lifetime of the application.

The front-integrated cover glass is sealed around the circumference with a chemical-resistant gap seal. In addition to the sensor, the most important component of a PCAP system for medical applications is a functionally reliable touch controller. EMC influences occurring in the environment of the application, e.g., in HF surgical devices, are reliably eliminated by special firmware algorithms. For applications in radiation-critical areas, such as MRI devices, an additional metal mesh foil is integrated into the sensor structure to shield the radiation. Furthermore, resistive touchscreen solutions in special designs such as glass- film-glass (GFG) or low reflection (LR - sunlight readable) and resistive multitouch are used for mobile medical devices for outdoor use.

A combination with capacitive switch elements (CapKeys) such as buttons, sliders and wheels or haptic membrane switches can be realised with all touch technologies.

Outdoor applications

For extreme outdoor applications, resistive GFG(glass-film-glass) touch screen technology is used in addition to specially developed PCAP sensors. Reliable function in snow and ice and daily sunlight UV radiation can be realised with this technology. Combined with the Low Reflective (LR) design, the reflection rate is minimised to 1.5%. This makes the display content of the application optimally readable even in direct sunlight.

The resistive multitouch (RMT) design is available if the application requires multitouch functionality. This RMT can be shielded with a metal mesh film on the front for medical applications.

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By Natasha Shek