William L Reichert wrote:
> We are having problems with filaments on our Delta Plus burning out
> quickly. After first filament went we replaced it. The next filament
> failed in 5 days. The following filament lasted 6 days. All the
> filaments had the center ~1 mm missing. Our IRMS uses the Conflo 3. We
> ran a slow magnet scans at various Conflo 3 helium settings. The
> spectra did not indicate that there was any significant air leaks into
> the system. Do you have any ideas on what could be causing the rapid
> filament failures?
I've gotten bum filaments before, but even those lasted a few months,
not days. I would suspect the filament current control. Sounds like it
could be passing too much current either due to lack of control, or from
poor measurement of the current.
Could also be its alignment with the trap. If the filament (or the trap)
is not aligned well, then it would take more filament current than
needed to get the specified current measured at the trap. Unless this is
limited somewhere independent of the trap. Not sure about that.
To check the filament current, *carefully* measure between P48 and J48.
According to my course book this should be around 3.65A
For the trap, *carefully* measure between P17 and J17. This should be
around 0.8 mA, depending on your settings. Source current should also be
around this, measured between P13 and J13. Good luck.
North Carolina State University
Dept. of Soil Science
3114 Williams Hall
Raleigh, NC 27695