[Sbs_gems] [Revised Logentry] GEM Gas Mixture Problem and Resolution

[ewertz at jlab.org]

Logentry Text:
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~21:30 - Alerted that there are gas mixture and pressure alarms on the BBGEMs. Pressures and gas mixture were increasing.  The problem actually started around 21:00.
~22:00 - After briefling looking at plots at home, got to the Counting House around this time. Shut off gas to the BBGEMs to ensure increasing pressure did not cause hardware damage. The GEM flows increase by about 75-100 cc/min per module. I need to confirm with UVA folks, but to my knowledge this is not the pressure limitation of the GEMs. See attached myaplot 
22:00-23:00 - Bhasitha and I checked a lot of common problems. The source of the problem was a bottle in one of the Argon slots that was mislabeled as both Argon and Nitrogen. The bottle actually contained Nitrogen. Having Nitrogen in the line explains why the Binary Gas Analyzer did not interpret the mix ratio correctly. Having Nitrogen instead of Argon could explain the slight increase in pressure, as the flow rates are calibrated for Ar/CO2. We replaced the Nitrogen bottle with Argon and purged the line for significant amount of time till the mix ratio was in acceptable operating condition
~23:25 - Mix ratio looks good enough. I reopen the valve to the BBGEM gas line to the detectors to the Hall. Initially I opened it too much. After realizing that I can change the valve adequately, I scaled back the pressure output to the Hall to match expected production conditions. 


Will flush BBGEMs for at least 1 hour or about 5 volume changes before turning HV back on to a GEM. This should commence about 00:30. 

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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/4121390
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