PCAP touch panels for outdoor applications

Outdoor application: PCAP touch panel on a tank system (Image: APRON)

Outdoor applications differ from indoor applications in many ways. Outdoor applications must meet higher specifications in terms of temperature and weather resistance for use in extreme weather. PCAP touch panel solutions master this challenge thanks to the selection and qualification of weather-resistant and functionally stable materials.

UV filter

Outdoor touch panels are almost always exposed to direct sunlight. Long-term exposure to UV rays damages the material and leads to yellowing, clouding and blistering, and even cracking of the touch sensors. These optical defects not only reduce the light transmission of the touch panel, but also its appearance. The wavelength of UV light (100 to 400 nm) is outside the range visible to humans. The glass on a PCAP touch panel only blocks UV wavelengths of less than 300 nm – thus also UVB and UVC radiation. Longer wavelengths are blocked by more than 95% thanks to the integration of UV filters. These UV filter materials are qualified to the ASTM G154 and MIL-STD810H standards, each with 1000 hours in an accelerated UV aging test.

weather test

Another qualification test is the so-called weathering or Florida test. This simulates the effect of the full spectrum of sunlight (295 – 800 nm) including rain on the touch panel. This test makes it possible to comment on possible UV damage after months or years of outdoor application within a short period of time. The UV filter function protects not only the PCAP sensors and the adhesive, but also the integrated display, thus preventing yellowing.

UV color print

The front glass is often printed with ceramic paint. However, ceramic printing offers only a limited range of colors, thicker layers of paint and high baking temperatures. By using UV-based, organic printing, a larger selection of colors can be realized with reduced layer thickness and identical light density. This printing technique also complies with the already mentioned standards. The qualification shows that the color does not change under UV exposure and the adhesion of the print remains stable over a long period of time. Printing with UV ink thus ensures optimal stability for PCAP touch panels for outdoor applications.

Quality check of PCAP panel printing

Quality check of PCAP panel printing (Image: APRON)

corrosion protection

Harmful gases from air pollution can lead to corrosion of components and contact surfaces in outdoor applications. For example, sulfur and nitrogen form sulfuric and nitric acids when they react with moisture. These harmful gases can cause oxidation and corrosion of the silver conductors on the PCAP touch panel. To protect the touch sensors, they are therefore designed in a pollution-proof design.

Weatherproof PCAP outdoor application

Weatherproof PCAP outdoor application (Image: APRON)

Extended temperature range

Outdoor touch panels are exposed to large temperature fluctuations every day. In extreme solar radiation, they must withstand temperatures of up to +80 °C. Touch applications in the outdoor area therefore require possible operating temperatures of -40 °C to +85 °C. Qualified materials are available for these applications meeting the storage temperature range from -50°C to +90°C. Using environmental simulations and long-term testing, these PCAP sensor materials and the optical adhesives were successfully qualified for outdoor applications.

Temperature stable regulators

In addition to the stability of the sensors, a regulator that also meets this operating temperature range is required. The PCAP system must also automatically compensate for changes in capacitance as a result of large temperature changes in the surroundings. This is ensured by special algorithms in the firmware of the controller used. Depending on the application and the resulting specific requirements, PenMount, ILITEK or EETI controllers are preferably used.

water repellent

Liquids on the touch panel surface have so far caused false triggering or malfunctions during use. Thanks to the further development of special evaluation electronics based on self-capacitance measurement, the functional reliability of PCAP and CapKey input systems is now even ensured under running water. As a result, physical keys can be completely dispensed with, and the buttons or sliders disappear behind glass as a CapKey solution.

PCAP touch panel in the sanitary area

PCAP touch panel in the sanitary area (Image: APRON)

New applications

The hardware and firmware of the PCAP touch buttons have also been optimized for conductive substances (e.g. salt water). This enables problem-free use in new areas of application. Even detergents or soapy water will not cause CapKeys to misfire. With this new design, water-resistant PCAP touch solutions are now also suitable for use in control panels in wet areas, marine equipment, medical equipment or sanitary applications.

Custom systems

The implementation of an optimal HMI solution requires a high degree of know-how and experience, especially for applications with extreme areas of use. All specifications and their special requirements in the application must be verified and qualified.

knowledge and experience

Thanks to many years of experience in the development and production of PCAP touch panels, SCHURTER offers high-quality, customer-specific input systems for every application. In close cooperation with our customers, our engineers develop and design the optimal solution for use under particularly demanding conditions.

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