From: Paul
Date: Sat, 05 Oct 2002 10:29:26 +0100
Subject: Re: [TSSP] TOPV breakout threashoul
Hi Marc, Yes, I recall your observations on the breakout from the bulb. You mentioned the use of a bulb in http://www.abelian.demon.co.uk/tssp/list/m.000579.html and later in http://www.abelian.demon.co.uk/tssp/list/m.000630.html > still no replies to my early work with bulb glass as a constant > breakout voltage test bed? Your observation that breakout occured at a repeatable voltage was interesting, but nothing new in that respect, since we are accustomed to things breaking out at 'some' voltage. Our difficulty is two fold, a) to actually measure that voltage, and b) to predict it in advance. The trouble with tests involving bulbs, both yours and Terry's, is that it's not possible for us to draw any useful conclusions from the situation. Nice and curious pictures, but for me, there's no data coming from it. The physical system of bulb, low pressure gas, glass wall, and awkward shape, together make for a system which is too complicated to analyse. We could, from knowledge of your coil, variace setting, etc, estimate the topvolts at which the bulb breaks out, but I don't see how we can relate that to any predictions. Yes, I am concerned that Terry figures most prominently in most of our results. Not that I wish to discourage Terry at all! But he does have the best equipment and lots of time to spend. I'm always looking for ways to take accurate measurements from coils without needing sophisticated and expensive equipment. This was fairly easy in the past, when we were measuring frequencies, etc, and lots of people were able to contribute. It gets more difficult as things progress, and lately, only Terry has been in a position to move things forward, eg with precision measurements of Q factors, voltage and current profiles. With the equipment available at your end Marc, your best bet would be to replace the bulb with a small sphere, with a well defined geometry so that we can calculate its surface field strength. Then you would have to measure peak topvolts indirectly by measuring peak base current. By using a small breakout sphere in conjunction with a normal sized toroid, the base current is a reasonably accurate way to get at the topvolts. You could look to see if the obvious breakout (clearly visible leaders) occurs at substantially higher voltage than we predict based on 26kV/cm, and you could look for signs of weak breakout occuring before that ie the faint cloud reported by Malcolm. It would be very nice if we could reproduce this and we might find that it occurs at roughly the expected voltage, rather than the 2 to 5 times higher at which the leaders are forming in our sample of one. In fact, just plotting a graph of base current against firing voltage might well reveal an early breakout. Indeed, we are so far out on our understanding at the moment, that precision measurement are hardly called for, and some quite rough measurements, eg just going by the firing voltage (scaling it up by sqrt(Lsec/Lpri)), would suffice to move things onwards. I do try to ensure that work is properly acknowledged, whether it is 'new' stuff, or otherwise, it all supports our collective efforts. I don't think we've failed to give credit where due. With respect to breakout voltages, there's precious little credit to go around, since we don't seem to be making much progress. > but what's the point in sharing? because a) you might be wrong, in which case it's helpful to have others correct your work, and b) you might be right, in which case we all want to know about it! > but i've always hated a "kiss ass" and a "credit grabber". I'm with you on that. But I don't see any of that going on. Happily, both pupman and tssp are 'open' - it's easy for anyone to pop up and say 'Oh yes, that agrees with what I found back in...'. There's not much chance for anyone to pull the wool over our eyes, I think. Marc, I hope you're not at odds with tssp or pupman. I honestly don't think you've any reason to be. Your frequency measurements were most valuable in that they allowed us to confirm our modeling of the secondary out to both large h/d and large inductance. I value your input and comment, as well as your measurements, because to me, you are one of the 'renowned coilers', with vastly more experience than I have. At they end of the day, all our theories and programs are meaningless unless they sit comfortably with experienced coilers. To me, your most important contribution is your presence on the list, knowing that you won't be afraid to speak up and say if something sounds stupid. That really is a very valuable thing for the group to have. -- Paul Nicholson, --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.