The use of a touchscreen interface for the control and input of a given computer system has become very popular for plant floor applications. It is now a fully accepted and understood method of effectively interfacing with industrial computer systems.
At one point, keyboards were the only means of interfacing with a PC until the development of a "pointing device" i.e., the mouse. Since then other pointing devices have gained favor for industrial applications such as joysticks and trackballs. Today, virtually all software applications require the use of a pointing device such as a mouse.

Another such "pointing device" is a touchscreen, which is the most direct form of operator interface since the operator is touching the actual area of the screen they want activated. It also serves as an intuitive tool for operators that are not as familiar with basic computer pointing devices. Touchscreens have found their way onto the plant floor for a number of reasons. One of these reasons is to eliminate the need for a keyboard or traditional mouse and provide operators with graphical icons that represent the specific task at hand. This serves to keep operators focused on the application and can be used by virtually all operators of regardless of their level of computer knowledge.

Another consideration for touchscreen technology in lieu of a traditional office-grade mouse/keyboard is the fact it is more industrial grade and resilient to the elements found on the traditional plant floor. Most touchscreen technologies can also be used with a gloved hand eliminating the need for the operator to remove their gloves prior to operating the computer system.


HOW IT WORKS
All touchscreens, regardless of the "technology", operate on the same principle as a mouse. They're nothing more than a pointing device in which the cursor is controlled by the operator’s finger or some other form of stylus. The cursor will then appear where the operator places his or her finger and can be dragged around the screen the same as a mouse would do. The touchscreen is self-calibrating to a given monitor size such that the initial set up takes less than five minutes. The operation is the same as with a mouse: click and drag, double clicks, etc. Via the set-up, it can be designed to "activate" upon touch or release of touch. All touchscreens are supplied with the necessary software drivers and interface cabling to work with most computer systems. The "interface" to the computer is via an available serial port.

A common misconception is that by adopting a touchscreen interface, you "give up" the mouse. This is not true. A touchscreen and a mouse / joystick / trackball can be connected to the same computer. Both can be used, just not at the exact same moment.

WHICH TECHNOLOGY IS BEST?
Once the decision to use a touchscreen has been made the next decision is which touchscreen technology is best. This can easily be determined by looking at the application, where the touchscreen will be used and the environment it will be operating in. There are four basic touchscreen technologies that are generally used: Resistive, Infrared, Capacitive and Surface Acoustical Wave (SAW). They all have their pros and cons as outlined below. Capacitive for example cannot be used with gloves but can be washed down whereas Infrared can be used with gloves but has some limitations in wet environments.

Some newer technologies, that hold promise are NFI (Near Field Imaging) and ThruGlass Capacitive. These are basically improved capacitive touchscreens with safety glass overlays that can be used with "gloved" hands. They provide a more robust interface for applications that involve more severe use.

TOUCHSCREEN COMPARISON

Resistive Technology
A thin glass substrate is "sandwiched" in between two layers of a plastic overlay. On the surface of the glass substrate is a tin oxide coating onto which a slight electrical current is constantly applied. The plastic overlay and the glass substrate are separated by hundreds of microscopic dot separators. When pressure is applied to the outside of the plastic overlay the two currents touch and a ground occurs. The X and Y coordinates of the touch are then detected by the touchscreen controller card that is installed in the PC.

Pros: Any pointing device can be used including gloved hands, suitable for washdown.

Cons: Surface can be cut with a knife, slight reduction in brightness
Rating: NEMA 4/4X, Class I/II, Division 1/2 with I.S. Barriers.

This is the "most" popular form of touchscreen technology that is used in industrial applications. It is the most cost effective and easy to use. Since it can be "sealed" to the NEMA 4 /4X standards most of the major HMI manufacturers have adopted this technology.

Infrared Technology
Miniature transmitters are located around the perimeter of the mounting bezel. These transmitters emit infrared light beams from top to bottom and right to left. Infrared light receivers are located on the opposite sides. When an object, such as a finger or stylus, then "break" this beam, the X and Y coordinates are detected.

Pros: Good clarity, gloved hands OK
Cons: May not suitable for direct washdown, subject to activation by flying objects
Rating: NEMA 12/4 / Class I/II, Division 1/2 with purging.