[Dsg-rich] RICH N2 Flow instablility

[Tyler Lemon]

Hello George, 

This morning, RICH interlocks tripped on low N2 flow as noted in logbook entry 3558672 (https://logbooks.jlab.org/entry/3558672). 

Looking at the flow history, it shows that the nitrogen flow dropped from 20 slm to 15 slm in about ten minutes. About ten minutes later, the flow had increased again to 20 slm, but has been unstable in comparison to before the drop in flow. We checked other detector's nitrogen flows and the only other we saw this on was the FT-calorimeter. 

Attached is a plot of the two RICH N2 flows and one FT-calorimeter N2 flow. The main point of the plot is to show the three nitrogen flows all showed the same flow patterns, so the plots are tiled to show all three signals. The Y-axis is for the blue RICH N2 flow #2. The FT-calorimeter's flow is significantly less, on the order of ~250 sccm, but its flow still show the same drop and instability. 

What would cause this change in flow? Could it be caused by Hall B's nitrogen dewar being refilled? 

Best regards, 
Tyler 
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