<html><body><div style="font-family: times new roman,new york,times,serif; font-size: 12pt; color: #000000"><div>Hi George,</div><div><br>After talking to Marc and you, it does seem that the drop in nitrogen flow was most likely caused by Hall B's nitrogen dewar getting refilled and the nitrogen supply pressure changing as it is filled.<br><br></div><div>Attached is a plot of RICH nitrogen flow data for about one month showing the same pattern of flow drops every 8-10 days or so. Only the drop this morning was large enough to trip the RICH interlocks.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div><span style="color: rgb(0, 0, 0);" data-mce-style="color: #000000;">Since this drop in flow seems to be regular, it raises the question of whether the RICH N2 flow interlock should have its lower limit changed so flow changes caused by dewar fills do not trip RICH's interlocks, disabling HV/LV.</span><br data-mce-bogus="1"></div><div><span style="color: rgb(0, 0, 0);" data-mce-style="color: #000000;"><strong><br data-mce-bogus="1"></strong></span></div><div><span style="color: rgb(0, 0, 0);" data-mce-style="color: #000000;">Best regards,<br data-mce-bogus="1"></span></div><div><span style="color: rgb(0, 0, 0);" data-mce-style="color: #000000;">Tyler<br data-mce-bogus="1"></span></div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><b>From: </b>"Tyler Lemon" <tlemon@jlab.org><br><b>To: </b>"dsg-rich" <dsg-rich@jlab.org><br><b>Sent: </b>Wednesday, April 11, 2018 8:30:16 AM<br><b>Subject: </b>[Dsg-rich] RICH N2 Flow instablility<br></div><div><br></div><div data-marker="__QUOTED_TEXT__"><div style="font-family: times new roman,new york,times,serif; font-size: 12pt; color: #000000"><div>Hello George,<br></div><br><div>This morning, RICH interlocks tripped on low N2 flow as noted in logbook entry 3558672 (https://logbooks.jlab.org/entry/3558672). </div><br><div>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.<br></div><br><div>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.<br></div><br><div>What would cause this change in flow? Could it be caused by Hall B's nitrogen dewar being refilled?<br></div><br><div>Best regards,<br></div><div>Tyler<br></div></div><br>_______________________________________________<br>Dsg-rich mailing list<br>Dsg-rich@jlab.org<br>https://mailman.jlab.org/mailman/listinfo/dsg-rich<br></div></div></body></html>