Rockwell Automation 6000 Industrial Computers Technical Reference Guide - Manual (Page 6)

display pixel. CRTs have a very fine pixel resolution, and can easily change between
display resolutions. LCDs are best used with the native-mode resolution, and there are
averaging errors when lower resolutions are used. Neither LCDs or CRTs can support
resolutions higher than their maximum rating.
Touchscreens
A touchscreen is a sensing device used as an operator interface option on computer
monitors. It acts as a transparent switch, passing on the operator’s finger or stylus
position when activated to the computer. The touchscreen driver interprets the physical
activation into location data on the desktop, much like a mouse driver. There are many
types of touchscreen technologies available: resistive, capacitive, infrared, SAW are
among the most common. RAC6000 computers use analog resistive touchscreens
exclusively.
Resistive Touchscreen
This touchscreen technology uses two sheets of a thin, transparent overlay material that
rests over the display surface. The two sheets are each coated with a conductive material,
and held apart by small spacer dots. When depressed, the two sheets close like a switch.
In matrix touchscreens, the sheets are screened with rows and columns, and the touch
resolution depends upon the row and column sizes. In analog touchscreens, a voltage
gradient is used so touch resolution is essentially infinite. The advantages of resistive
touchscreens are high touch resolution, good durability, easy to panel seal for NEMA4
applications, and impervious to false activation from surface dirt and debris. The
disadvantage of resistive touchscreens is reduced display brightness caused by the two
overlay sheets.
Capacitive Touchscreen
This touchscreen technology uses a single sheet of thin, transparent overlay material that
rests over the display surface. The single sheet is coated with a conductive material, and
driving by an oscillating voltage gradient. When a human figure comes in contact with
the material, water in the skin disrupts the voltage field, and the contact position is
decoded by the interface electronics. The resolution is essentially infinite. The
advantages of capacitive touchscreens are increased display brightness with only a single
overlay sheet, and easy to panel seal for NEMA4 applications. The disadvantage is that a
bare human finger is needed to activate the touchscreen. Gloves or stylus devices cannot
be used.
Infrared Touchscreen
This touchscreen technology uses a border of infrared LEDs and sensors around the
display surface. The IR beams are broken when the display surface is touched, and the
position then decoded by the interface electronics. The advantages of infrared
touchscreens are the display brightness not affected by any overlay material, and there is
no overlay that can be damaged by cutting or abrasions. The disadvantages of infrared
touchscreens are limited touch resolution, difficult to panel seal, and sensitivity to false
activation from surface dirt, water, and debris.