Is the CRT dead?



 

ISO 13406-2

The ISO 13406-2 (International Standards Organisation) depicts criteria for brightness, contrast, reflection, uniformity and maximum defective pixels allowed. There are essentially four classes of quality allowed, one to four with one been the highest. One is usually found in medical and military spec displays, two is most common in the computer and consumer markets whilst the other two are more or less becoming defunct as manufacturers produce better quality displays at a cheaper price. The ISO standard specifically governs how many ‘always lit pixels and sub-pixels’, ‘always unlit pixels and sub-pixels’ are allowed. Most panels have their ISO criteria listed in the warranty terms of the associated product. Notebooks as well.

CRTs

The manufacture of CRTs, very much like thermionic valves (it is one too) is on the decline. The issue here is that CRTs are no longer as cheap to manufacture as LCDs and although they both have their inherent strengths, LCD panels are digitised whereas CRT displays are almost all analogue. CRT displays have a lot of high energy circuits which are prone to failure – a) Switched mode power supplies (although used in both), b) deflection circuits (the H-deflection circuit is a high energy circuit and is prone  to failure), the high voltage circuit using a device called a LOP-T (line output transformer) which incorporates the tripler circuit (up to 25KV) is prone to failure and is nowadays hard to come by for older models.  Many manufacturers of displays no longer manufacture CRT based displays. BTW CRT displays for computer use are multi-standard as a rule – the SVGA monitor for instance can run at many different resolutions but this all carries a price tag: More costlier components which had to be switched through relays in large screen monitors. LCD panels use one circuit – a pre-scalar, a one chip device which used to be very expensive but no longer for entry level monitors. Yes, the CRT has one very big advantage – text can be read at difefrent resolutions but not so with LCDs. LCDs have a native resolution which makes text readable otherwise it appears fuzzy and is sometimes so bad cannot be read at all. From my side I don’t see any advantage of manufacturing CRT displays anymore but having said that I hate the display on digital oscilloscopes – it’s a case of getting used to though and there again a CRT has no apparent advanatge, least of all mobility. Modern test equipment is mainly hand held – at a price of course. I was at a seminar in 2001 where a Viewsonic engineer said that they were phasing out CRT monitors – this was also at about the time that Panasonic started moving Viewsonic graphics and professional series monitors to China for manufacture. I stand under correction but China is currently the largest manufacturer still to bring out CRTs albeit to a disinterested first world market. A 15″ CRT monitor now goes for about 50U$ and a 17″ for about 60U$ which still makes them attractive in developing countries. China are also exporting entry level LCDs with exceptional picture quality at about 120U$ for a 19″ so the days of the CRT in developing nations is also going to become a thing of the past. Remember also that most CRT monitors cannot be adapted easily for battery usage – a must in some African countries or out in the field.

However for colour fidelity many graphics artists stay with their tried and trusted 21″ CRTs.  That is until their professional series monitor loses it’s FBT (Fly Back Transformer).  The brilliant Viewsonic 800 series monitors all seemed to fail at some stage or other, falling prey to the FBT – if my memory serves me correctly they had an 817 monitor with unparalleled performance, even in terms of today’s display performance.

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