Yes, I agree! It gives a bit of insight to what "Cathode poisoning" actually refers to.
Thanks for typing this up! Michel On Apr 25, 10:24 pm, Imbanon <[email protected]> wrote: > Finally a good answer to this question. That was very informing. > Thanks! > > On Apr 25, 10:26 am, "JohnK" <[email protected]> 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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