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Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
I just fired up my diffusion pump today and of course the ionization gauge to measure the pressure. It worked great and everything until I looked up at the gauge and only about an eighth of the filament was glowing! It was also flickering a bit. Also, the glass on that side of the tube was discolored blueish. The strange thing is that this gauge was working great for a good hour. I did operate it continuously from the point when the diffusion pump kicked in at about 10 mTorr. Is that what caused it?
On another note, will inadequate water flow cause my diffusion pump to not reach the pressure that it is supposed to? I noticed that the pressure ceased decreasing at only about 6x10^-4 Torr (the same time I noticed the problem with the gauge).
Does anyone know where I can learn about the technique of operating an ionization gauge? I'm just guessing with the different calibration knobs right now. I can make the needle vary anywhere from 0 to 10 on the meter at any given selected range.
Also, at the moment I have a temporary mounting for the gauge. It has about a 3/16 in hole to the chamber... I know that is way too small and that will be fixed soon. Could that be a cause of my problems?
Registered Member #2372
Joined:
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Posts: 62
On our digital ion gauge controllers they wont turn on until it goes below 1 mTorr so I dont know if you should use it at such a high pressure. Also, they arent really very accurate, maybe a factor of 2 or so, this was determined one time when we stuck like 7 ion gauges on the same chamber and they were all different. it is possible that your system only pumps down to 6x10^-4 because there is leaks in it, especially if it sort of asymptotically approaches that pressure. You can determine this by making a pressure vs time graph as it pumps down.
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Ionization gauge and other vacuum stuff
