On 1/25/12 10:56 AM, Derek, Extreme Electronics wrote:
Bob, I agree will all you have said, apart from one item. I come from the UK where inches and mm are interchanged regularly. (and with more success than NASA) So I have always used the rule of thumb of 25Kv per inch as this equates to a rule of thumb as 1Kv per mm. This Rule of thumb satisfies both measurement systems more easily I think...
Except that it's wrong.In a needle gap, yes, 25-30kV/inch is reasonable, but it's highly dependent on the size of the needles and the distance.
In a uniform field gap (or something very close.. sphere gap with spacing small compared to diameter of sphere), a 30kV/cm or 70kV/inch is a better thing.
For a rule of thumb in construction, a clearance distance of 10-20kV/inch is good. 10 is pretty conservative, 20 is a bit bolder. It really depends on the radius of the conductors, of course.
And, just to defend NASA, who pays my salary, it was the contractor who delivered data (in US Customary units) that did not conform to the published interface spec, which is in metric/SI, as are ALL deep space missions. It never occurred to anyone in the deep space navigation business that someone would do something like use pounds instead of newtons. You can fault the JPL folks for not catching the error, but in reality it was a "system failure" (i.e. a bunch of stuff aligned just wrong to result in the error).
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