Attachments to CAT Chat Minutes - March 15, 2004
Report on Oxford Cryo-Pump Auto Restart Package
A few weeks ago, I reported at CAT chat that we had simulated the Oxford restart package and found that a situation presented itself where restart did not occur. This was a consequence of tying the timing circuit of Timer 2 to the DC supply. If line transients occurred, timer 2 may not "see" them since the "collapse" of the DC supply is slower than the transients and a restart pulse would NOT be generated. The solution found in the lab was to tie the timing signal for timer 2 directly to the AC line. This was demonstrated in the lab and was also demonstrated on a cryo-controller. The ME group is looking to make up a connector to bring the AC source into the chassis housing the restart package. As soon as a suitable rework package (for both B & C type coolers) is decided upon, it will be offered to users requesting this change. Change will be done by the ME group.
During the week of 3-8-04, Reggie Wright (a consultant to Oxford) was on site and in talking with him, he said he had looked into this same problem and had arrived at the same conclusion that we arrived at in the lab. Apparently, he reported this to Oxford over a year ago but it was not disseminated very well to owners of Oxford cryo-pumps containing the restart package. The good thing is that independent investigation resulted in the same conclusion.
1) Minimum Generator Start and Transfer Times (by Greg Markovich)
2) The schematic for simulator used noting "fix" "Oxford Cryo-pump Restart Simulator" (by Bill Wesolowski)
3) "Report on Investigation into Auto-restart Problem" (by Reggie Wright)
4) Two sheets from Oxford on the original restart package. (Circuit & set-up)
5) Instruction for setting the timers in the auto restart package and recommended settings based on information regarding generator start and transfer times.