Finally a good answer to this question. That was very informing. Thanks! On Apr 25, 10:26 am, "JohnK" <yend...@internode.on.net> wrote: > I have noticed many discussions about the lifetime specifications of Nixies. > I haven't noticed anyone quoting the manufacturer definition of lifetime - > but I may have missed it. So, read on ....... > > "Electronic Counting circuits techniques devices ", Mullard Limited, October > 1967. approx. 220 pages. Many circuits. > Various authors and sources. > There seem to be about eight of these books available through ABE ranging $20 > to $60. Bound to be others at the usual places too. > > The approx 13 page chapter on numerical indicator tubes is based on material > supplied by B. Butler of the Mullard Industrial Electronics division. > > I have included some of the text below rather than attach scans [if allowed], > John Kaesehagen > Australia. > > From the 'numerical indicator tubes' chapter I quote this [via OCR] :- > "The normal figures quoted in published data for the life of a numerical > > indicator tube are 5000 hours with a continuous display of one character, > > and 30 000 hours when sequentially changing the display from one digit > > to the next every 100 hours or less. The end of life for the above figures is > > taken to be the time when any character is unable to be covered completely, > > although several more thousand hours would probably have to elapse > > before the character became completely indecipherable." > > The above is contained within this section:- > > " LIFE PERFORMANCE > > The expected life performance of a numerical indicator tube depends to > > a greal extent on the length of time the discharge is investing any particular > > cathode. With any gas-discharge device, the cathode is subjected to constant > > ion bombardment which removes material from the cathode and > > deposits it elsewhere in the tube. This "sputtering" process, as it is known, > > is, in fact, put to good use in many cold cathode gasfllled tubes during > > processing. The cathode surlaces are cleaned in this manner and any > > sputter material thrown on the glass walls of the envelope effectively seals > > in any foreign matter that may affect the performance of the tube during > > its life. In a numerical indicator tube, however, although a clean cathode > > is desirable, sputter material on the envelope would impair the visibility > > of the display. Some sputtering is unavoidable, but since the rate of > > sputter is proportional to the peak current of the tube, it can be contained > > within limits. > > If one cathode is continually glowing, sputter material from that > > cathode is deposited on other cathode surfaces in close proximity. > > Although the legibility of the glowing cathode is not affected to a great > > extent, the cathodes on which the sputter is deposited are affected. In > > fact, the work function of the metal of the adjacent cathodes alters in > > such a way that it requires a higher current to completely cover the > > cathode and if this current is not available, the cathode appears patchy. > > This imposes a minimum permitted current level on the tube. It is possible > > that complete erosion of the cathode may result from bombardment, > > but this is unusual. > > If the discharge is cycled betweerr characters fairly regularly, this gives > > a very much improved life figure since each cathode, although receiving > > some sputter material, is subjected to the cleansing action of bombardment. > > In this case, the higher the current, the more effective the cleansing. > > The viewing area of the envelope is protected from sputter material by > > the use of a shield, or mesh, which is usually connected to the anode. > > From the foregoing it is evident that the end of life of a numerical > > indicator tube is not abrupt, but takes the form of a gradual deterioration > > of a character. This is convenient, because it enables a tube which is > > showing signs of deterioration to be replaced before it fails completely. > > The normal figures quoted in published data for the life of a numerical > > indicator tube are 5000 hours with a continuous display of one character, > > and 30 000 hours when sequentially changing the display from one digit > > to the next every 100 hours or less. The end of life for the above figures is > > taken to be the time when any character is unable to be covered completely, > > although several more thousand hours would probably have to elapse > > before the character became completely indecipherable. If a tube is > > operated with a bulb temperature below 0"C, the mercury inside the tube > > condenses, resulting in a slight increase in the sputter rate. However, if > > the consequent shortening of life can be tolerated, an operating temperature > > range of -50 to +70"C can be achieved. "
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