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.

Check out our blog, Insituation, 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

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