[Hallb-engineering] FW: Hall B Eng Meeting summary

[A.M. Sandorfi]

This morning¹s meeting was devoted to a review of events that caused the
4/18 IBC magnet quench and how to prevent that trouble scenario in the
future, Below is a brief summary from Chris Bass.


------ Forwarded Message
From: Christopher Bass <cbass at jlab.org>
Organization: Jefferson Lab
Reply-To: <cbass at jlab.org>
Date: Fri, 20 Apr 2012 11:28:34 -0400
To: "A. Sandorfi" <sandorfi at jlab.org>
Subject: Hall B Eng Meeting

Andy,
 
Here is a brief write-up of what was discussed at the 20 APR 2010 Hall B
engineering meeting this morning.  Could you forward this info to the
appropriate people.
 
Christopher
 
 
* We discussed the probable causes of the IBC magnet quench on 18 Apr 2012:
 
The liquid helium level in the IBC is monitored by a Labview program that
runs on the HDICE computer in the Hall. That program sends the liquid helium
level information to the EPICS network via an IOC (clonpc1). Liquid helium
supplied by a buffer dewar is used to fill the IBC, and that flow is
regulated by a valve (EV8215) that uses the EPICS signal of IBC liquid
helium level as a control input. Due to a router switch failure, the signal
coming from the HDICE computer was interrupted, so the EPICS signal stopped
refreshing with current values.  The PID-control regulated the valve based
on an unchanging EPICS signal, which closed the valve to its minimum set
point position.
 
When the router switch was reset, the EPICS signal refreshed with the
current liquid helium level in the IBC, and the PID-control opened the valve
up to adjust flow based on this new value.  The previous reduced flow had
warmed up the transfer line between the buffer dewar and the IBC, so when
the flow increased, warm gas was initially pushed into the IBC.  This
further lowered the liquid level in the IBC, which contributed to the magnet
quenching.
 
 
* We discussed possible solutions to prevent this failure mode from
happening again:
 
1) Create a program that monitors the EPICS signals of the IBC, which will
check if these values are refreshing. If the EPICS signals don¹t refresh
within a short amount of time, then an alarm will notify personnel in the
counting house.
 
2) Install a hardware signal from the IBC to the valve, which bypasses the
network.
 
3) increase the minimum set point position of the liquid helium valve
(EV8215), to ensure that the transfer line between the liquid helium supply
dewar and the IBC doesn¹t warm up due to a small helium flow.
 


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