On Jan 17, 2018, at 3:02 AM, Wolfram Meier-Augenstein (pals) <[log in to unmask]> wrote:Hi Jennifer,
You are right, it could be something to do with the source such as two connecting wires being too close or even touching occasionally (thus tripping the source).
BTW, a loss / reduction of signal after source maintenance can occur if the source flange does not sit dead-centre resulting in a partial eclipse of the gas inlet.
However, that doesn’t really explain the “jumpy” beams. One possible culprit could be a dodgy part on the source control board. Another could be the power supply unit, and yet another could be the power supply to your lab. Would you happen to know how the power supply to your lab fits within the bigger picture of the building where lab is housed? Conversely, if everything was fine prior to December, was there any work down to power supply and the way power is routed in your building that might affect voltage and how free of spikes / brown-outs the power is in your lab?
My first IRMS lab got its power (initially) from a line that also fed the lifts (elevators) and some other heavy-duty users in the building. The effect on our instruments was such we could not run samples during normal working hours. Beam intensity over time scans looked like recordings of earth tremors.
**********************************Prof. Dr W Meier-Augenstein, CChem, FRSCStable Isotope Forensics & Analytical Sciences
School of Pharmacy & Life SciencesThe Sir Ian Wood BuildingGarthdee Road
Stable Isotope Forensics book, 2nd edition: https://www.wiley.com/en-gb/Stable+Isotope+Forensics%3A+Methods+and+Forensic+Applications+of+Stable+Isotope+Analysis%2C+2nd+Edition-p-9781119080206
Once again my EA-DeltaPlusXL system is giving me problems and I’m not sure why. An iffy power supply is one possibility but I’m not convinced. Here is the sequence of events … note that the source keeps tripping off:
Late November to early December we cleaned the source, changed pump oil, cleaned the Penning gauge, and fixed an EA problem.
Dec. 10 the source tripped off overnight (voltage off, emission on). It turned back on OK but no beams. Played around with the tuning and got my beams back but the sensitivity did not recover until the next day.
Stabilities were fine so I ran some N-only samples for a few days.
Dec. 17 the nitrogen backgrounds and reference gas signals were too low. Decided to rebuilt the source using all new ceramics and replace one of the x-deflection half plates because it had a dent (…not sure how you dent one of these but that’s what it looked like). Made darn sure there were no bits of metal stuck to the source magnets.
Dec 27 sensitivity and stability were OK.
Jan 3 noticed that the water background was really low and beams were a bit jumpy. Started a run of tests any how. Sadly this run failed because the source tripped off (…as it did on Dec. 10 prior to the source clean)
Jan 4 the source turned back on OK. Stabilities looked good even though the beams were jumpy and water was still low (...but not as low as it had been because I had bypassed the He purifier). Restarted the run of test samples and the results looked fine.
Jan 5 and 6 was able to run some N-only samples . No problems.
Jan 7 the sensitivity was low so I retuned. Beams still jumpy.
Jan 12 the stability has gone to “heck”, beams really jumpy. Retuning (increasing Extraction Symmetry and decreasing X-deflection) seems to help but it only lasts a few minutes.
Jan 15 the source tripped off again but turns back on as per the last two times.
Jan 16 same problems as the 15th but in the process of troubleshooting I turned the source off and on and lost my beams. Found them again by changing from CO2 to N2.
My best guess is that I have charging in the source. Anyone have other ideas? If not, I’m pulling the source out again.
Bye for now,Jennifer
Assistant Professor (Senior Research)
Stable Isotope Lab Manager
CEOAS, Oregon State University
Corvallis, Oregon 97331
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