I’m hoping someone can help me with
a problem that has developed on my MAT252. I recently went through a flurry of
bad refurbished filaments (no trap emission) and now that I have a nice new filament
in there, I can’t get the source, or pumps, to stay on more than a couple
minutes after turning the voltage up to the full 10 KV. I haven’t yet
opened the ConFlo, so it is in dual inlet mode. I left it overnight with the HV
at 8 KV, and the pumps were still going this morning, but the HV was off (source
control still on). HV reset OK. Vacuum was at 3.6 E-9. Within 2 minutes of
turning on the HV to 10 KV, the pumps tripped again. I’m lucky now in
that after half a dozen trips over the last three days, I’ve at least
figured out how to reset the pumps before they vent so that I don’t lose
vacuum. As long as I am in the room.
I’ve had a similar problem to this
in the past, and the problem was with a couple capacitors the vacuum gauge
monitor, which was giving faulty signals causing the trips. At that time, the
needle valve on the analogue vacuum display had been “jittery” and
then outright failed. And the inlet forevacuum display in Isodat had been
jumping around. But I haven’t seen the same symptoms this time, except perhaps
that the vacuum during CF mode seemed slightly lower than normal (2.6 E-6 as
opposed to 4 E-6). I note that the vacuum gauge display is not responding at
all when the pumps trip, until I can reset the MS, restart Isodat system, and
toggle the vacuum display buttons. Toggling the buttons is a trick that has always
been necessary from time to time to get the analogue display to respond. Until
the analogue vacuum gauge display returns to an active reading mode, the pumps
will not restart. As with my earlier problems, this suggests a possible problem
with the vacuum gauge monitor again. However, I don’t recall there being
a link before to having this happen only with HV at the full 10KV.
And here is another piece to the puzzle…
I just decided to keep an eye on the source forevacuum (through the analogue display
since I can’t figure out how to get it to display through Isodat) to see
if it was displaying any odd behaviour. Since I have switched it to this
setting, still at 10 KV, it hasn’t tripped yet. As I write this it’s
only been 1 ½ hours, but it hasn’t tripped yet. I couldn’t
get more than 2 minutes of run time this morning and yesterday when set at 10KV
while monitoring source high vacuum.
Does anyone out there recognize these
symptoms? At this point I’m still thinking it is the vacuum gauge
monitor. I should know by the end of the day whether this is directly related
to the analogue display being set to the source high vacuum at 10 KV only, or
whether it is a fluke that it hasn’t tripped again.
Thanks for any insight.
--Alison
Stable Isotope Lab Coordinator
CREAIT •
TERRA Facility • Stable Isotope Lab
Alexander Murray Building
Memorial University of Newfoundland
St. John's, NL •
ph: (709) 737-3217 •
fax: (709) 737-2589