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FAQ - A visual vacuum gauge for newbies with no gauge

Posted: Fri Dec 27, 2019 6:07 am
by Richard Hull
Most newbies tend to blow all their initial money on a vacuum pump and some sort of chamber, put a grid in it, pump it down and apply power. The result is the normal diffuse pink glow of lots of air in a poorly sealed demo fusor. First light for most is disappointing in that what they have is miles away from the star produced at low pressures in a good demo fusor. Naturally, they have no good electronic vacuum gauge.

What is the problem?? Leaks and bad pumps are always the cause. The easy test is to get a vacuum gauge and seal better then test again. Keep resealing and running your pump until you get as low as you can go. If still not successful, you know your pump is probably at fault.

For those Newbies who want to make a good guess at their pressure, Jon Rosenstiel provided a great visual vacuum gauge years ago in these forums and I will point you to it. By comparing your visual effort at pump down to Jon's calibrated, measured vacuum levels, you can get a good idea of where you are in your vacuum efforts.

To make the best comparisons, you should have a variac controlled power supply to adjust your voltage from 0 to some voltage around 7000 volts. A neon sign supply is ideal. Make sure to have a current meter in the ground line of the supply. To match Jon's images, you must raise your voltage and match Jon's current of 5mA to create the same conditions. Also you should be in a very dark room to make the background black as in Jon's images.

I have annotated Jon's images to note the fine points and differences related to the glow between successive images. Here is his great visual vacuum gauge posting.


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Richard Hull