Hi folks,
I am still working on Nixie tubes, but I have to take it a little slow
at the moment because I switched my university and I am currently sort
of living in two cities ;-)
However, today I had some time so I took a look at my vacuum system. My
problem was that even after I closed the valve to my pump at a pressure
of 1.5E-2 mbar, the pressure would rise up to 20mbar in 20 minutes. So
there was a leak.
I then checked every part of my system (swagelok adapter, needle valve)
by replacing them with a blind flange and recording the pressure after
10s, 20s, 30s, 40s, 50s, 60s, 120s, 300s, 600s, 1200s and plotted them.
I realised that there was insufficient greasing on my needle valve, and
the most interesting thing is that it is not airtight if the scale is
adjusted to just zero. You have to (gently) adjust it below the scale
zero point. Then I get a leakage rate of just 1.2 µbar/s which is very low.
My system has a volume of at most (!) 65ml, so the leakage rate now is Q
= 5.4E-6 mbar l/s which is pretty good I think. See my results here:
http://www.jb-electronics.de/tmp/leakage.png
http://www.jb-electronics.de/tmp/leakage_extensive.png
Note that the Q value in these diagrams needs to be multiplied with 65ml.
The next step will be to find a good connection to the pressure reducer
for my gas bottle. Right now I am using a PVC hose (terrible), and I
have huge leakage rates.
But as always: One thing at a time ;-)
Jens
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