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This has been a very timely discussion. I just replaced the filament in our Delta V Plus. Although I did not experience your issue of low box and trap currents I did experience a lack of stability even after a 1 day pump down. I noticed that the vacuum was at 7.6e-007 mBar with the inlet closed; this is usually around 7.5e-008 mBar. After reading this discussion I decided to re-seat the source. I centered the source as Paul suggested prior to applying vacuum and I also carefully tightened the four retaining clamps in a crosswise pattern to a torque of "just snug". In US terms it would have been in the low inch pounds. After another day of pumping everything is stable and back to normal vacuum. It appears as though seating the source "O" ring prior to applying vacuum avoids a small leak. I was not able to confirm this with Argon due to the safety interlock on the door to the source, one that I did not want to defeat. 

Hope this helps,

Todd Brown
Monsanto
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-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Herb J. Tobias
Sent: Thursday, May 19, 2011 5:42 PM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Delta V, trap and box current

If you have to open the source, check to see whatever filament you use is aligned to the center of the slit in the ion source. You probably know this but thought it might be worth a mention.

Regards
Herb
________________________________________
From: Stable Isotope Geochemistry [[log in to unmask]] On Behalf Of Patrick McLoughlin [[log in to unmask]]
Sent: Thursday, May 19, 2011 2:41 PM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Delta V, trap and box current

Paul,

It sounds like two different things are occurring. You replaced the filament and the box and trap currents as well as the filament current are all the result of the new filament - and if I'm not mistaken the specs you give are good/average for a new filament. The other half is that you introduced a slight misalignment of the source when you re-inserted it after the filament change. We fought that battle once for quite some time, and the result was that by simply removing and replacing the source (with a little more care the second time) our signal returned. Replacing the source is at least 90% art - it is a "feeling" thing, impossible to put into words - sorry.


Pat McLoughlin, Ph.D.
Technical Director
Microseeps, Inc.<http://www.microseeps.com/>
Check out our blog, Insituation<http://mail/exchweb/bin/redir.asp?URL=http://www.insituation.net/>, for discussions and insights into our cutting edge tools!



From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Paul Eby
Sent: Thursday, May 19, 2011 1:36 PM
To: [log in to unmask]
Subject: [ISOGEOCHEM] Delta V, trap and box current

Hello all,

I've just replaced a blown filament on my Delta V, and am getting strange results with the replacement. Signal is way down (50mV from 5V), and both box and trap current are ~0.6mA (instead of 0.7 or 0.8). Filament current is 1.5mA. If I drop the filament current, the box and trap remain at 0.6mA until I reach 1.2mA on the filament: below that, both box and trap also drop, remaining at approx 50% of the total for each.

Do these symptoms suggest anything to anyone?

Paul Eby
[log in to unmask]
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