Choose the Best Industrial HMI

01/31/2007




Industrial Displays

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January 31, 2007

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Choose the Best Industrial HMI
Knowing the environmental constraints and the technology that best operates within them, you can choose rugged interfaces that withstand the rigors of the plant floor or in-vehicle operations.



Everyone knows that delicate and temperamental equipment has no place on the plant floor. The dust and doughnut-crumb hazards that threaten office equipment are nothing compared to the temperature swings, moisture spikes, electrical noise and physical abuse most industrial machines endure. So if you're searching for an operator interface for such a rugged environment, you need equally rugged technology behind it. To choose the best industrial HMI, consider these six environmental factors, which can dramatically and adversely affect the usability of an interface.

Temperature
Most displays in operator interface terminals are specified to operate in 0 to 50s it becomes thicker and takes longer to respond to electrical fields. If exposed to extreme cold, it may freeze and crack the display. Terminals operating in extremely cold temperatures can be equipped with a heater to warm the LCD display and prevent it from freezing. High temperatures adversely affect LCD displays as well. The liquid crystal responds to heat the same way it does to electrical fields. Heat causes the light to be blocked, turning the display black. If the display gets too hot, the liquid crystal fluid can boil and bubbles can appear in the display. Terminals operating in changing temperatures can be equipped with a temperature sensor to adjust the back light and contrast of the display as the temperature changes.

Moisture
Industrial devices typically have humidity ratings similar to office equipment, but liquid spills, chemicals and washdown environments will wreak havoc with non-ruggedized terminals. Numerous organizations (NEMA, CSA, UL, IEC) rate enclosures for their ability to remain sealed against moisture, and some technologies are better than others at withstanding it. Capacitive touchscreens can be compromised by moisture, for example, and terminals with acoustic wave touchscreens can be difficult to seal.

Shock/Vibration
While most electronics today are solid state, components like LCD displays are susceptible to shock and vibration, and are often the weakest link. Because vibration is typically not an issue in office environments, it may not be included in specification sheets from vendors unfamiliar with the industrial market. Most automation devices have shock ratings in the range of 15 to 25 G using the IEC 61008 specification, and industrial vibration amplitude ratings in the range of 1 to 5 G.

Electrical Noise
Electrical noise is an invisible hazard that can create mysterious and intermittent problems. The accuracy of capacitive touchscreens, for example, is somewhat dependent on the electrical characteristics of their surroundings. Automation devices typically meet the IEC 61000-4 series of specifications to protect against several types of noise, including transients, electromagnetic interference, burst on data lines, and the like. These specifications are typically two to three times more rigorous than the EN-55024 ratings used to specify office equipment.

Dirt, Glare, Gloves
Ambient lighting and potential for glare can affect the type of display you choose. Controlled lighting conditions on the factory floor require one configuration, while a different screen or filter may be needed outside in the sunlight or in the cab of a vehicle used both day and night. For in-vehicle applications where the ambient lighting is constantly changing, a terminal with an ambient light sensor might be needed so the user is not continually adjusting the display lighting. Keypads and touchscreens, on the other hand, are affected by different physical factors. Membrane polydome keypads seal better against dirt, for example, while dispersive signal touchscreens work well when operators' hands require gloves.

Choosing the best industrial HMI for your application involves knowing your environment and the technologies that are best suited to it. The engineers at QSI Corporation have been making operator interface terminals suited for rugged industrial environments for more than twenty years. They're experts on industrial specifications and the LCD, touchscreen and communications technologies that best meet them. For more information, click here to receive QSI's 'Operation Interface Buyers Guide Whitepaper.' Or visit www.qsicorp.com to learn more about QSI's complete line of rugged terminals and their Qlarityobject-based programming language, which makes hardware configuration fast and easy.

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