I have replaced a blown filament on our Delta V Advantage, and pumped it for one day (baked inlet, analyzer, inlet valve overnight, and source heater on). The vacuum was 1.9e-007 with inlet valve closed and it was still decreasing. I turned on the filament current with inlet valve closed, and Box was 0.80mA and Trap was 0.69mA. Mass 28, 29, 30 were 7, 85, and 196 mV and they decreased at first. However, the signals started to increase after 200 sec. Mass 30 starts to increase first, then mass 29 increases 50 sec after mass 30 started to increase, and mass 28 in the end. The same thing happened for CO2 and argon.
I suspected a leakage, and checked all fittings with argon spray and tightened all fittings. Nothing changed.
If this was due to a leakage, I would expect gas amounts in the source continue to increase while filament is off. However, signals seems to decrease during filament is off, and start to increase only after filament current is turned on.
For example, when I turned on the filament in the morning, mass 44, 45, 46 were 31, 96, 123mV. They started to increase 150-250 sec after the filament current is on, at a rate of about 0.5mV/100sec. I turned off the filament (Src heater on) and left it pumped more. In the afternoon, I turn filament on again, the signals are much lower, 13, 44, and 54mV. Then about 200 sec after filament is on, they started to increase again. Vacuum is still decreasing nicely.
I took source out and checked there are no wires in short, no loose wires, and no dust or fabric on source. Filament alignment looks ok (to me). Tried different filament (batch 03.08.2016). Baked inlet, analyzer, and inlet valves overnight. The same thing, increase in signals, happens when filament is on.
By chance, I turned off source heater, and found signals immediately decreased. It decreased to low, 5, 7, 12 mV (mass 28, 29, 30) and 4, 8, 10 mV (mass 44, 45, 46), and the increase did not happen. As soon as I turn on the source heater, signals increase at 0.5mV/100sec.
After this, I turned off filament and turned on source heater. Waited for 2 hours. Turned on filament (with source heater on), and the CO2 signals are 5, 10, 12mV. A bit higher than 2h ago, but not as high as signals increased at 0.5mV/100sec.
It seems mass 28, 29, 30, 40, 44, 45, 46 increase at the same rate.
Vacuum continued to decrease. It is now 1.67e-007 with inlet valve closed, and increases if source heater is on. It decreases with source heater being off. In the morning when Vac was 1.9e-7, vacuum was just decreasing with source heater on/off and an increase was observed only in signals at that time.
Has anybody observed this? I would appreciate help.
p.s. All metals were cleaned and sonicated in type I water, methanol, and hexane, and then dried at 90 degree C for two days in an oven, as usual. Ceramic parts were not replaced because they looked clean.