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A touch screen is an electronic visual display that allows the user to control an electronic device simply by touching the icons on the display. The touch screen technology in industries makes navigating simple and quick for operators.
In the industries, hardware input devices such as mice and keyboards are being replaced by touchscreen technology. The use of a touch screen for HMI ensures efficient functioning, improved user performance, and enhanced productivity. While selecting a touch screen technology for your application, you need to consider a lot of factors. In this article, we will discuss the resistive and capacitive touch screens that are commonly used in industrial automation.
Resistive touch screens have two layers that are either made of PET film or glass/ polycarbonate plastic. Glass usually makes up the bottom layer, and glass or film makes up the upper layer. Depending on the application, alternative pairings such as glass/glass and film/film are also used. Each pairing offers its own specific features. However, both layers have a uniform resistance value over their whole surface.
Indium Tin Oxide (ITO), a transparent metal oxide, is deposited on the inner surface of each of the two layers. When voltage is applied, ITO allows for a gradient across each layer for touch point detection. The bottom and top layers in touch screens are separated by an air gap and the spacer dots that are generally present on the bottom layer. The spacer dots prevent the top and bottom layers from touching each other when no pressure is applied.
The resistive touch screen technology works in a simplified manner. The two layers in them act as the voltage divider. When the pressure is applied to the touch screen, the top layer bends to make touch with the bottom layer. This results in a change in resistance between the two layers and, as a result, a change in current. The controller interprets this change, and the software determines the actual contact point.
The electrodes in resistive touchscreens develop a uniform voltage throughout the whole conductive surface. This delivers a precise voltage reading corresponding to the area of layers that contact each other when pressed. In this section, we will discuss three common types of resistive touch screen technologies. Each type offers different durability and sensitivity.
In a 4-wire analog resistive touch screen technology, both the top and bottom layers have two electrodes (busbars) perpendicular to each other. The top layers’ electrodes are oriented along the positive and negative Y-axis, while the bottom layer’s electrodes are oriented along the positive and negative X-axis. Using this type of electrical-coordinate configuration in this type, the controller senses the coordinates when the two layers touch each other.
In 5-wire analog resistive touch technology, the bottom layer has four electrodes on four corners. These electrodes are linked via four wires. The fifth wire is a sensing wire embedded in the top layer. When touch is registered on any layer, this sensing wire transmits the specific voltage corresponding to the coordinates to the controller or processor. This type is more robust since it has fewer components and a simple design.
The 8-wire sensing circuit is the most sensitive resistive touch screen technology. It differs slightly from 4-wire analog touchscreens. Each electrode in this touch technology has two wires instead of one. This adds a layer of redundancy to the circuit. If one of the wire pairs loses resistance over time, the second wire continues to deliver a secondary signal to the CPU. That implies a more costly resistive touchscreen with an 8-wire analog circuit will be more durable. It also eliminates the drift issues present in other types of resistive touchscreens.
Resistive touchscreens offer the following benefits.
Cost Effectivity: Resistive touch screens are economical. Because of the design simplicity of the touchscreen and its corresponding controllers.
Power Efficiency: They consume less power as compared to other touch screen technologies.
Liquid and Contaminant Resistance: Resistive touch screen panels are resilient to liquids and contaminants such as dust and water.
Easy Input Detection: Because resistive touchscreens are pressure-sensitive, they may be used with any input device, such as a gloved hand or a pen/stylus. These screens do not require a conductive item like capacitive touchscreens.
Higher Sensor Resolution: Resistive touchscreens have more sensors than capacitive touchscreens. That’s why a finer tip functions better in resistive touch technology. Users can choose a fine-tipped stylus whenever the icons on an app are tiny.
High Response Rate: Resistive touchscreens offer a quick response to the input.
Fewer Accidental Touches: Light touches are not detectable by a resistive touchscreen. That’s why resistive touch screens are preferred in an environment when there is the anticipation of accidental touches on the screen. These touches can be from rainfall or liquid fall etc.
Usage under Harsh Environments: The standard resistive touch screens are sensitive to harsh temperature and humidity fluctuations, which can damage the precision of the touch screen.
But they handle the harsh environmental conditions better than capacitive touchscreens. That’s why resistive touch screens are still preferred over capacitive touchscreens in outdoor environments.
Resistive touchscreens come with the following drawbacks.
Display Clarity: Resistive touchscreens come with only 75% clarity. They display low-quality images as multiple films are layered in the structuring of these screens. People with limited eyesight may face additional challenges as a result of this. In these touchscreens, the ITO coating of the top flexible layer cracks because of the continuous stretching and retraction of this layer. Which also contributes to the deterioration of the air gap between the ITO layers. The spacing among the conducting layers permits dirt and dust to gather, reducing the display clarity even more over time.
Inability to Self-Calibrate: The performance of resistive touch screens is affected by the continuous distortion and warping of the ITO layer. This modification necessitates recalibrating the screen again and again.
Easy to Damage: The top hard-coated layer must be thin enough to sustain the touchscreen panel’s flexibility. As a result, sharp items, scratching, and poking can easily damage this layer.
Low Optical Transmissivity: Resistive touchscreens offer low optical transmissivity (less than 80%). The presence of two layers of PET/ glass, an air gap, and spacer dots in the manufacturing of resistive touchscreens can result in a loss of refractive and reflecting light, resulting in a more blurry and shaded display.
Aging: Another disadvantage is that resistive touchscreens suffer the process of aging, which begins to happen when PET film degrades at high temperatures. The indicator of aging is touchscreen discoloration, in which the touchscreen display begins to turn white.
No Support to Multitouch: Resistive touch technology does not support multitouch since it only responds to one location input. It does not support the use of two-finger gestures.
Size Limitation: Resistive touch technology is hard to build in sizes larger than 27 – 28 inches due to the difficulties of making a uniform ITO coating for large size layers.
A capacitive touch screen has an insulator such as glass with a transparent conductor coating. This coating material is usually Indium Tin Oxide (ITO).When there is a touch on the screen, a little amount of charge is attracted to the point of contact. Circuits in each corner of the screen measure the charge and transmit it to the controller for processing.
The most used capacitive touch technologies are;
In surface capacitive technology, the conductive coating is present only on one side of the insulator, and four electrodes are present on four corners of the touchscreen. When a small modest voltage is applied to the conductive layer, it results in an electrostatic field. This field is uniform over the surface area of the conductive layer. A capacitor is developed when a conductive surface (e.g., a human finger) comes into contact with an uncoated surface. The controller attached to the sensor infers the touch’s position from the capacitance change recorded from the four corners of the screen.
In this technology, a single layer of conductive material is etched to make an X-Y grid pattern of electrodes, or two separate and perpendicular layers of conductive material with parallel lines or tracks etched to form the X-Y grid. The capacitance of the closest conductive traces is changed when a conductive object(e.g., a finger) is placed on a grid of conductive traces. The change in trace capacitance is monitored, and the touch position is calculated. An X-Y grid allows for better resolution than resistive technology.
Capacitive touchscreens offer the following benefits.
Multi-Touch Technology: Capacitive touch screens can identify and measure multi-touch locations simultaneously. This Multi-touch technology is used to serve a purpose similar to the function keys (Control, Alt, Option, Command, and so on) on a regular keyboard. However, advancements in hardware can enable multi-touch to allow several users to simultaneously use the same device, such as the Microsoft Surface 300+ touch capability.
Durability: The strength and durability of capacitive touchscreen technology are other significant advantages. These touchscreens are more durable than resistive touchscreens, especially when subjected to heavy use.
Requires Less Pressure: Capacitive touchscreens detect touch using the electrical current of the human body and need less pressure to function than resistive touchscreens. To operate a capacitive touchscreen, you just need to drag your finger across the surface.
Cracked Screens Continue to Function: Minor cracks do not affect the operation of a capacitive touchscreen. It continues to measure the electrical charge generated by the operator and uses this information to establish where the contact happened.
Optical Clarity and Readability: A capacitive touch screen offers more clarity than resistive touch screens. It offers amazing image quality because of the usage of a glass layer.
Liquid, contaminant, and scratch-resist: The double-glass layout in the capacitive touch technology efficiently prevents the adverse effects of external environmental elements on the touch screen. The capacitive touch technology still computes the touch position accurately even when the screen is covered with dirt, dust, oil stains, etc.
Support personalized customization: Capacitive touch screen sizes are customizable by the factory to meet the demands of the users.
The drawbacks of using capacitive touch screens are the following.
Cost Inefficient: Capacitive touchscreens are more expensive than resistive touch screens. The price tends to rise exponentially with an increase in display size.
Power Inefficient: These screens consume more power than resistive touch screens.
Limited to capacitive objects as input: Proper static charge interference is required to register a touch on capacitive screens. Hence only selective input objects such as bare fingers can interact with these screens. Which restricts the usage of these screens in hazardous environments where gloves use is a must.
You need to consider various factors while selecting the touchscreen to automate the industry. A few of them are listed below.
Each touch screen technology has its benefits to offer. This table will summarise all the features offered by both.
|Feature||Resistive Touch Screen||Capacitive Touch Screen|
|Response Time||< 10 milliseconds||< 15 milliseconds|
|Intense Light Resistant||Good||Bad|
|Touch Resolution||Very High||Normal|
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