<HTML>
<HEAD>
<TITLE>FW: Hall B Eng Meeting summary</TITLE>
</HEAD>
<BODY>
<FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>This morning’s 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.<BR>
<BR>
<BR>
------ Forwarded Message<BR>
<B>From: </B>Christopher Bass <<a href="cbass@jlab.org">cbass@jlab.org</a>><BR>
<B>Organization: </B>Jefferson Lab<BR>
<B>Reply-To: </B><<a href="cbass@jlab.org">cbass@jlab.org</a>><BR>
<B>Date: </B>Fri, 20 Apr 2012 11:28:34 -0400<BR>
<B>To: </B>"A. Sandorfi" <<a href="sandorfi@jlab.org">sandorfi@jlab.org</a>><BR>
<B>Subject: </B>Hall B Eng Meeting<BR>
<BR>
Andy,<BR>
<BR>
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.<BR>
<BR>
Christopher<BR>
<BR>
<BR>
* We discussed the probable causes of the IBC magnet quench on 18 Apr 2012:<BR>
<BR>
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.<BR>
<BR>
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.<BR>
<BR>
<BR>
* We discussed possible solutions to prevent this failure mode from happening again:<BR>
<BR>
1) Create a program that monitors the EPICS signals of the IBC, which will check if these values are refreshing. If the EPICS signals don’t refresh within a short amount of time, then an alarm will notify personnel in the counting house.<BR>
<BR>
2) Install a hardware signal from the IBC to the valve, which bypasses the network.<BR>
<BR>
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 doesn’t warm up due to a small helium flow.<BR>
<BR>
<BR>
<BR>
------ End of Forwarded Message<BR>
</SPAN></FONT>
</BODY>
</HTML>