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AVIONICS TECHNOLOGY are packed together in stripes or clusters called "triads." Color CRTs have three electron guns, one for each primary color, arranged either in a straight line or in a tri- angular configuration (the guns are usually constructed as a single unit). A grille or mask absorbs the electrons that would otherwise hit the wrong phosphor. This type of display does have a tendency to degrade with age and over time will loose luminescence result- ing in costly replacement. Display intensity can be controlled either by an external dimming circuit or by an ambient light sensor. It has been observed that when a CRT has gone through a repair process, the biasing of the internal dimming circuits may no longer be calibrated to the aircraft cir- cuitry and in some cases when full brightness is selected an over bias condition occurs resulting in some E G O M E loss of definition in the display. Another rather negative tendency is the "screen burn in effect," where an image can be etched in the display if allowed to remain unchanged for extensive periods of time. This coupled with the effects of heat should always be consid- ered when deciding how long a system should remain energized during a maintenance event. CRTs can emit a small amount of X-ray radiation as a result of the electron beam's bombardment of the phosphors. The amount of radiation escaping the front of the monitor is widely considered safe; however, they may contain toxic substances, such as cadmium within the phosphors. At low refresh rates (below 50 Hz), the periodic scanning of the display may produce an irritating flicker that some people perceive more easily than others, espe- GET COMPLIANT MEET EPA AIRLINE A DRINKING WATER RULE T Choose Purogene® The #1 recommended product for potable water disinfecting of aircraft water systems and ground support equipment. P.A.S.S.® Airline Sanitation Systems will automatically blend Purogene® and Activator at the recommended dilution ratios eliminating hand mixing. Learn more at AeroSafeProducts.com/GetPurogene or call 404.855.1539 SCAN FOR SPECIAL SAVINGS cially when viewed with periph- eral vision. A high refresh rate (above 72 Hz) reduces the effect. Computer displays and televisions with CRTs driven by digital elec- tronics often use refresh rates of 100 Hz or more to largely eliminate any detectable flicker. Liquid crystal display The liquid crystal display (LCD) is the current panel of choice for many avionics manufacturers. LCDs are more energy efficient and offer safer handling and dis- posal than CRTs. Its low electrical power consumption enables use in many energy critical conditions such as backup instruments where emergency battery power may be required. It consists of an electroni- cally modulated optical device made up of any number of pixels filled with liquid crystals and installed in front of a light source Visit us at NBAA Booth #N4729 www.AMTSociety.org • www.AMTonline.com • Aircraft Maintenance Technology September 2011 25