Touchscreen monitors have become more and more commonplace as their price has steadily dropped over the past decade. There are four basic systems that are used to recognize a person's touch:
- Resistive
- Capacitive
- Surface acoustic wave
- Infrared
RESISTIVE
The resistive system consists of a normal glass panel that is covered with conductive and resistive metallic layers. These two layers are held apart by invisible spacers, and a scratch-resistant layer is placed on top of the whole setup. An electrical current runs through the two layers while the monitor is operational. When a user touches the screen, the two layers make contact in that exact spot. The change in the electrical field is noted and the coordinates of the point of contact are calculated by the computer. Once the coordinates are known, a special driver translates the touch into something that the operating system can understand, much as a computer mouse driver translates a mouse's movements into a click or a drag. Resistive Touchscreens are very durable, and 5-wire resistive technology is more reliable than 4 or 8 wire technologies.
Advantages
- high touch resolution
- works with any stylus, gloved hand or finger
- not affected by dirt, dust, water or light
- least expensive of all technologies
Disadvantages
- 75% clarity
- not vandal or scratch proof
- not recommended for high heat environments
- harsh chemicals are a problem
CAPACITIVE
In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. Frequency changes are measured to determine exactly where the touch event took place and then relays that information to the touchscreen driver software.
One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.
Advantages
- high touch resolution
- high clarity
- not affected by dirt, grease or moisture
Disadvantages
- only be operated with a finger
- fingernail, stylus or card will not activate the screen
- deep scratches on screen will cause failure
SURFACE ACOUSTIC WAVE
With surface acoustic wave technology, acoustic waves are sent across a clear glass panel with a series of transducers and reflectors. When a finger touches the screen, the waves are absorbed. causing a touch event to be detected at that point. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics.
Advantages
- high touch resolution
- high clarity
- no-drift operation, little need for recalibration
Disadvantages
- hard stylus such as pen will not work
- susceptible to dirt, dust and/or water as unit is not completely sealable
- deep scratches on screen can cause failure
INFRARED
Infrared technology is a technology that can withstand severe environments including direct sunlight applications using transflective technology. The glass is vandal and abrasion restant as there are no sensors on the glass. A series of infrared beams determines the point of contact on the screen.
Advantages
- high touch resolution
- high clarity
- no-drift operation
- withstands severe environments
Disadvantages
- grid housing of Infrared is the weakest area
- most expensive technology
SUMMARY
With Resistive technology it doesn't matter if you touch the screen with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave and infrared technologies works much like the resistive system, allowing a touch with almost any object -- except hard and small objects like a pen tip.
As far as price, the resistive system is the cheapest; its clarity is the lowest, and its layers can be damaged by sharp objects. Infrared usually has the highest clarity, but is usually the most expensive.