WHITE PAPER - TOUCH SCREENS IN INDUSTRIAL COMPUTER SYSTEMS

What is a touchscreen?

A touchscreen is any monitor, based either on LCD (Liquid Crystal Display) or CRT (Cathode Ray Tube) technology, that accepts direct onscreen input. The ability for direct onscreen input is facilitated by an external (light pen) or an internal device (touch overlay and controller) that relays the X,Y coordinates to the computer.

Resistive Touchscreen Technology

Resistive LCD touchscreen monitors rely ona touch overlay, which is composed of a flexible top layer and a rigid bottom layer separated by insulating dots, attached to a touchscreen controller. The inside surface of each of the two layers is coated with a transparent metal oxide coating (ITO) that facilitates a gradient across each layer when voltage is applied. Pressing the flexible top sheet creates electrical contact between the resistive layers, producing a switch closing in the circuit. The control electronics alternate voltage between the layers and pass the resulting X and Y touch coordinates to the touchscreen controller. The touchscreen controller data is then passed on to the computer operating system for processing.

How Resistive Touchscreens Work

1. Polyester Film
2. Upper Resistive Circuit Layer
3. Conductive ITO (Transparent Metal Coating)
4. Lower Resistive Circuit Layer
5. Insulating Dots
6. Glass/Acrylic Substrate
7. Touching the overlay surface causes the (2) Upper Resistive Circuit Layer to contact the (4) Lower Resistive Circuit Layer, producing a circuit switch from the activated area.
8. The touchscreen controller gets the alternating voltages between the (7) two circuit layers and converts them into the digital X and Y coordinates of the activated area.

Because of its versatility and cost-effectiveness, resistive touchscreen technology is the touch technology of choice for many markets and applications. Resistive touchscreens are used in food service, retail point-of-sale (POS), medical monitoring devices, industrial process control and instrumentation, portable and handheld products.

Resistive touchscreen technology possesses many advantages over other alternative touchscreen technologies (acoustic wave, capacitive, Near Field Imaging, infrared). Highly durable, resistive touchscreens are less susceptible to contaminants that easily infect acoustic wave touchscreens. In addition, resistive touchscreens are less senstive to the effects of severe scratches that would incapacitate capacitive touchscreens. For industrial applications, resistive touchscreens are a more cost-effective solutions than Near Field Imaging touchscreens are.

8-Wire Resistive Technology

Resistive touchscreen technology exists in 4-wire, 5-wire, or 8-wire forms. Chassis Plans LCD touchscreens specifically employ 8-wire resistive technology because of its benefits over 4-wire and 5-wire touchscreens. Whereas 8-wire FastPoint touchscreens are available in all sizes, 4-wire resistive technology is restricted to small flatpanels (<10.4"). In contrast to 5-wire resistive touchscreens, 8-wire touchscreens do not experience spacer dots and Newton rings. Neither 4-wire nor 5-wire resistive technologies can account for the problems of high-level short-term varianecs and axis linearity and drift that 8-wire resistive technology solves