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Choosing the Right Touch Technology
For some applications, a "dual" touch, or touching two or more locations at the same time, is required. While no touch panel is particularly well suited to this, matrix touch technology can be a solution. A special class of touchscreens, matrix analog, is designed to register dual touches. Under some circumstances, infrared and surface acoustic wave also can be implemented for dual touches.
Touch Resolution
All touch technologies, with the exception of matrix, have sufficient resolution to accept finger input. A finger touch is generally about .25 inches (6mm) wide. Typically, a touchscreen controller will report coordinates of 1024 by 1024 pixels. The larger the screen, the fewer the points per inch, because resolution remains constant while the number of lineal inches goes up. Because most displays have fewer than 1024 pixels on each axis, touchscreens are at least pixel accurate. Where pen point resolution is necessary, only analog resistive has sufficient resolution to match the pen point.
Image Quality
Image quality is one area where the non-resistive technologies outperform resistive touch systems. Infrared touch has no glass or other barrier in front of the display, and yields the best image. Capacitive and surface acoustic technologies make use of a glass surface over the display. Typically the glass is either clear, which can cause mirror-like reflections, or anti-glare (etched), which reduces reflections but slightly distorts the image. Analog resistive shares these limitations, exacerbated by the fact that there are several reflecting surfaces between the display and the point of touch.
Cost Analog resistive and matrix systems are, by far, the least expensive touch technology. While, in theory, the capacitive sensor should be the least expensive, it requires more costly control electronics. Control functions can be added to analog resistive and matrix touch products with the use of single-chip touch controllers, which are not available for capacitive, infrared and surface wave acoustic touch systems.
Durability
The maximum life of a touchscreen is estimated to be less than 50 million touches in any one location. Each of the technologies discussed here is capable of meeting this expectation. Infrared and surface acoustic wave should, theoretically, have a nearly unlimited life, but for a variety of reasons, they don't last forever. Capacitive sensors can wear out, but extra non-conductive coatings on the touchscreen surface all but eliminate this concern. The materials used for analog resistive sensors have greatly improved over the last few years to the point where they show little or no wear over the useful life of the touchscreen - analog resistive sensors are, in fact, the technology of choice for pen input on hand-helds. After several years of use and millions of touches in the same location the protective coating can wear out, although improved coatings promise to eliminate this problem on new units.
Vandal Resistance/Breakage
Vandalism of touchscreens falls into two categories: permanently damaging the terminal, and incapacitating the system. The touch system least vulnerable to damage is infrared, followed by surface acoustic wave, capacitive, and matrix/analog resistive. On infrared touchscreens, LEDs are hidden behind an infrared-transmissive bezel. Only glass and coated glass are in front of the display on surface acoustic wave and capacitive screens. Analog resistive screens use a hardened polyester substrate as the outer surface, although a determined vandal with a sharp knife might be able to cut the surface. Because most people are aware of the explosive (actually implosive) nature of CRTs, vandals have been reluctant to take a hammer to terminals.
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