Touch screens are widely used throughout many daily devices including kiosks, certain vending machines, ATMs, mobile phones, and others. They all use touchscreens to empower the user to collaborate with a computer or device, all without the benefit of a mouse, trackball, joystick or keyboard.
The five most frequently used touchscreens are: 5-wire resistive, projected capacitive, surface capacitive, infrared, and surface acoustical wave (SAW).
5-wire resistive is the most widely utilized touch technology. A resistive touch screen is made up of conductive layers; a normal optical glass surface covered with two metallic layers, one being resistive and the other conductive, and finally a scratch resistant protective screen covering it all. As the user touches the LCD screen the pressure creates a contact between the resistive and conductive metallic layers. A change in the electronic field is then monitored. This transition is then recorded by the electronic circuitry used within the device and the data is passed on to the firmware which, in turn, processes and then forwards on the data to the devices operating system. The operating system will then produce a visual display on the screen of the captured motion or action (click or mouse drag etc.).
- Can be activated with virtually any object – finger, stylus, gloved hand, pen, etc.
- Has tactile feel
- Lowest cost touch technology
- Low power consumption
- Resistant to dust, oil, grease, moisture, and other liquids
- Lower image definition compared to other touch technologies
- Outer polyester film is vulnerable to damage from scratching, poking, and sharp objects
- Diffuses the light output of the LCDs backlights
This type of touch technology works in a noticeably different way to that of a resistive touch screen. On top of the LCD front window glass, a layer is placed that stores an electrical charge. Once this special layer is touched, a very small electrical charge is transmitted to the finger which came into contact with the screen, effectively reducing the amount of charge on the layer. This change in electrical charge is monitored by touch sensors which are located at the corners of the touch window. The sensors then pass on the data to the device driver software and then on to the operating system and in turn a visual if then display is produced. With a capacitive touch screen display, a conductive input arrangement must be used such as a finger or specific input device.
- Much better image clarity than resistive touch screens
- More durable screen than that of the resistive type
- Excellent resistance to surface contaminants and liquids- dust, oil, grease, water droplets
- High scratch resistance
- Does not diffuse the light output of the LCDs backlights
- Requires bare finger or specific capacitive stylus for activation
- Sensitivity to Electro-Magnetic Interference (EMI) and/or Radio Frequency Interference (RFI)
Projected capacitive is similar to surface capacitive, sometimes called PCAP or PCT, is an ideal preference for a wide range of applications, including industrial usage such as process control terminals, medical displays and agricultural vehicle telemetry systems because the touch performance in unaffected by scratches, dust and dirt on the touch window. Compared to surface capacitive technology, PCAP offers two primary advantages: In addition to a bare finger, it can also be activated with surgical gloves or thin cotton gloves. For some PCAP windows, they can also be operated by a user wearing heavy gloves, and can be sealed to high ingress protection ratings making them suitable for challenging or outdoor deployments. PCAP also enables multi-touch activation (simultaneous input from two or more fingers). A projected capacitive screen is composed of a sheet of glass with embedded transparent electrode films and an integrated chip which creates a three dimensional electrostatic field. When a finger comes into contact with the screen, the ratios of the electrical currents change, and the computer is able to detect the touch points.
- Excellent image clarity
- More resistant to scratching than surface capacitive touch screens
- Resistant to surface contaminants and liquids- dust, oil, grease, moisture
- Multi-touch (two-touch)
- Sensitive to EMI/RFI
- Must be activated via exposed finger, thin surgical or cotton gloves, although some PCAP windows (like those used by AbraxSys) can be triggered by a heavy gloved hand
Surface Acoustic Wave (SAW)
SAW touch screen monitors utilize a series of piezoelectric transducers and receivers along the sides of the monitor’s glass plate to create an invisible grid of ultrasonic waves on the surface. When the panel is touched a segment of the wave is absorbed. This enables the receiving transducer to locate the touch-point and send the data to the computer. SAW monitors can be activated by finger, gloved hand, or special mechanical stylus.
- Excellent image clarity
- Even better scratch resistance than that of capacitive touch windows
- Long touch life
- Will not activate with hard items such as a mechanical pen, finger nails or even a credit card
- Water droplets may cause false-triggering & activation
- Solid contaminants on the screen can generate non-touch areas until the dirt/dust is removed
Infrared Touch (IR)
Infrared touch screen technology does not overlay the LCD display window with an additional screen. Alternatively, infrared displays use IR emitters and receivers to create an invisible grid of light beams across the screen, both horizontally and vertically creating an “X” and “Y” axis. This ensures the best possible image quality since there is no overlaying window on the LCD screen itself. When an object interrupts the invisible infrared light beam, the sensors are able to locate the touch point.
- Highest image clarity and light transmission of all touch screen technologies
- Unlimited “touch-life”
- Impervious to surface scratches
- Accidental activation may occur because infrared beams are actually above the glass surface
- Dust, oil, or grease buildup on screen or frame could impede light beam causing malfunction
- Sensitive to water, snow, and rain
- May be sensitive to ambient light interference
- Higher cost
So, those are the five most widely touch technologies. Other types do exist, including AbraxSys’ HARDENED ARMORED RESISTIVE TOUCH.
For Armored Touch, a micro-thin sheet of borosilicate glass is laminated to the ITO polyester top sheet used in the typical construction of resistive touch sensors. This process produces a flexible glass membrane which is scratch resistant, water proof and impervious to chemicals, fire and stylus use. The resulting touch sensor is ideally suited to Military, Industrial, Mobile, Public Kiosk and Medical applications. Configurations are from 8.4″ to 24.0″.
Touch Screen for Harsh Industrial Environments
All touch screen interfaces have advantages and disadvantages, depending on their application. For industrial use, typically there are demands, conditions and distinctions that contribute better to certain types of touch screen interfaces.
The most commonly used and possibility most advantageous touch screen technology for harsh duty industrial and automation environments aims to be resistive touch screens. Since resistive touch screens allow the use of gloves and/or mechanical stylus usage, the user will not be bothered with having to remove gloves or protective wear in order to use the device.
Some industry facilities, like food and beverage for example, require a strict “no exposed glass” policy. Resistive touch technology employs a flexible polycarbonate (in most cases) top-sheet over a glass substrate. Resistive touch screens prevent any exposed glass and allow for usage throughout most industrial applications.
Many types of touch screen interfaces can excel in many environments, so it’s best to research what the application environment will be, including other project parameters, before selecting the type of touch screen interface that would be ideal for your application.
Touch Screen Comparison
|5-Wire Resistive||Surface Capacitive||Projected Capacitive||SAW||Infrared|
|Sensor Substrate (Top Coating)||Polyester top sheet. Glass substrate with ITO coating||Glass with ITO coating||Glass with ITO coating||Glass with ITO coating||Any substrate|
|Ease of Touch Activation||XXXXX||X||XX||XXX||XXXX|
|Accuracy and Repeatability||XXX||XX||XXXXX||XXXX||XXX|
|Sensitivity to Rain/Snow||XXXXX||XX||XXXX||XX||XXXXX|
|Sensitivity to Cleaning Chemicals||XXX||XXXX||XXXXX||XXX||XXXXX|
|Sensitivity to Surface Contaminants||XXXXX||XX||XXXX||XX||XX|
|Sensitivity to Ambient Light||XXXXX||XXXXX||XXXXX||XXXXX||XX|