Comment drytek2 SNF 2009-09-12 14:00:58: Comparison of 1Torr and 10 Torr heads ....

shott at snf.stanford.edu shott at snf.stanford.edu
Sat Sep 12 14:00:59 PDT 2009


This morning I conducted a more thorough examination of the new 1 Toor MKS manometer head.
To do so, I found another 10 Torr head with a KF flange and a separate PDR (power/display/relay) unit.
I had them both connected to drytek2 at the same time.
I then compared them at full pumpdown, the 150 mTorr pressure normally used during oxygen descum and at the 300+ mTorr setting when in standby mode.
For the new 1 Torr head I measured:
0 mTorr base pressure: 0 volts
150 mTorr readout: 1.60 volts
305 mTorr readout: 3.16 volts
Under the same conditions, the 10 Torr external head read:
0 mTorr base pressure: 0 volts
142 mTorr readout: 0.141 volts
288 mTorr readout: 0.287 volts
So, I am pretty convinced that we are now controlling to a pressure of preetty close to 150 mTorr with the controller setting on the 10 V scale.
I'm also convinced that at one point .... I don't know when .... that we did have a 10 Torr head, rather than a 1 Torr head, on drytek2.
Finally, we may need to adjust the PDR relay outputs .... I think that they are currently set for a 10 Torr head with low and high relay switching occurring at about 23 mTorr and 2070 mTorr, respectively.  With the existing 1 Torr head, those values become 2.3 mTorr and 207 mTorr .... and should likely be bumped up by a factor of 10, if possible. I'm not going to do that, however, until others have a chance to read and comment on this entire line of thinking.
Thanks,
John




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