Outdoor applications differ in many ways from indoor applications. Outdoor applications must meet higher specifications for temperature and weather resistance for use in extreme weather conditions. To meet these challenges, there are weatherproof and functionally stable PCAP touch panel solutions specially qualified for outdoor applications.
Outdoor touch panel applications are exposed to direct sunlight. Long-term UV exposure thus damages the material and leads to yellowing, clouding and bubbling or 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 visible range. The glass of a PCAP touch panel blocks UV wavelengths of less than 300 nm - thus also UVB and UVC radiation. Longer wavelengths are blocked by more than 95 % through the integration of UV filters. These UV filter materials are qualified according to ASTM G154 and MIL-STD-810H standards with 1000 hours each in an accelerated UV ageing test.
Another qualification test is the so-called weathering or Florida test. In this test, the effect of the entire spectrum of sunlight (295 - 800 nm) including rain sprinkling on the touch panel is simulated. Within a short time, this test enables a statement to be made about possible UV damage after months or years of outdoor application.
The UV filter function not only protects the PCAP sensors and the bonding, but also the integrated display, thus preventing yellowing.
UV colour printing
Printing on the front glass is often done with ceramic ink. However, ceramic printing offers only a limited choice of colours, thicker ink layers and high baking temperatures. When using UV-based organic printing, a larger colour selection can be realised with reduced layer thickness and identical light tightness.
This printing technique also passes the standards already mentioned. The qualification shows that the ink does not change under UV influence and the adhesion of the print remains stable over a longer period of time. Thus, printing with UV inks ensures optimum stability for PCAP touch panels for outdoor applications.
Harmful gases caused by air pollution can lead to corrosion of components and contact surfaces in outdoor applications. Sulphur and nitrogen, for example, form sulphuric and nitric acid when they react with moisture. These harmful gases can cause oxidation and corrosion of the silver conductive paths of the PCAP touch panels. To protect the touch sensors, they are therefore designed to be impermeable to harmful gases.
Extended temperature range
Touch panels in outdoor applications are exposed to large temperature fluctuations every day. In extreme sunlight, they must be able to withstand temperatures of up to +80°C. Touch applications in outdoor areas therefore require possible operating temperatures from -40 °C to +85 °C. Qualified materials are available for these applications that meet the storage temperature range of -50°C to +90°C. Through environmental simulation and long-term tests, these PCAP sensor materials and the optical adhesives have been successfully qualified for outdoor applications.
In addition to the stability of the sensors, a controller is required that also fulfils this operating temperature range. The PCAP system must also be able to automatically compensate for capacity changes caused by strong temperature changes in the environment. This is ensured by special algorithms in the firmware of the controller used. Depending on the application and its specific requirements, PenMount, ILITEK or EETI controllers are preferred.
Up to now, liquids on the touch panel surface have caused false triggering or malfunctions in the application. Thanks to the further development of special evaluation electronics based self-capacity measurement, the functional reliability of PCAP and CapKey input systems is now ensured even under running water.
This means that physical buttons can be dispensed with and the buttons or sliders can be integrated behind the glass as a CapKey solution.
New application possibilities
The hardware and firmware of the CapKeys have also been optimised for conductive substances (e.g. salt water). This enables an operation without malfunctions in new application areas. Even cleaning agents or soapy water do not cause the CapKeys to be triggered incorrectly. Water-resistant PCAP touch solutions can be used in many applications where liquids can cause malfunctions such as outdoor applications, marine equipment, medical devices and sanitary applications.
Particularly in applications with extreme environments, the realisation of an optimal HMI solution requires a high degree of know-how and experience.
All specifications and their special requirements in the application must be verified and qualified.
Know-how 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 optimum solution for use under particularly demanding conditions.