[Dsg-rich] RICH N2 Flow instablility

[George Jacobs]

This is just for general knowledge.

--- The purpose of an interlock is to either;
#1 Protect from something "bad"
or
#2 Prevent something "bad"

Now for the obvious question, What does the LOW N2 flow interlock 
either, #1 Protect? or #2 Prevent? Nothing I can determine, but it did 
turn off the detector for no real reason and perhaps ruin the data from 
that run.

--- The purpose of an alarm is to warn and or inform the shift/oncall 
persons to investigate and/or troubleshoot. In this particular 
situation, perhaps an alarm would be more useful than an interlock.

IMO, interlocks which do not protect or prevent bad things are self 
defeating. This case is a good example. However, a properly set up alarm 
would be my preference if it were my experiment.

Cheers,
George

On 04/11/2018 08:30 AM, Tyler Lemon wrote:
> 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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-- 
  
George Jacobs
Jefferson Lab (TJNAF)
STE 12
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Newport News, VA 23606

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(email) jacobsg at jlab.org

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