[Dsg-rich] RICH N2 Flow instablility

[Valery Kubarovsky]

I set the low limit for the N2 flow to 5 temporary and made request for the alarm 
on the N2 flow1 and 2. As soon as this alarm will be implemented I will remove these 
parameters from the interlock. 
Valery 

> From: "Tyler Lemon" <tlemon at jlab.org>
> To: "dsg-rich" <dsg-rich at jlab.org>
> Sent: Wednesday, April 11, 2018 8:51:57 AM
> Subject: Re: [Dsg-rich] RICH N2 Flow instablility

> Hi George,

> 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.

> 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.

> 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.

> Best regards,
> Tyler

> From: "Tyler Lemon" <tlemon at jlab.org>
> To: "dsg-rich" <dsg-rich at jlab.org>
> Sent: Wednesday, April 11, 2018 8:30:16 AM
> Subject: [Dsg-rich] RICH N2 Flow instablility

> 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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