Log entry time 17:10:39 on April 15, 2008

Entry number 232236

keyword=Rt Q3 He lvl gauge false readback during ESR recovery

I volunteered to reset the magnets for Vince because I was the only tech here in the counting house area (everybody else was doing something). Everything reset normally except for right Q3. The helium level gauge was oscillating wildly between 88 and 28 percent, and the pid loop on the top fill valve wasn't allowing the magnet to fill (CEV72Q304 = ~30%). The max open setpoint was about that same value. The magnet temperatures were all around 7.5K. Pete volunteered to open the top fill valve manually, and I put the Cryomagnetics gauge into continuous read mode. The He lvl immediately drove to 6.1% and stayed there. The temperatures came down to about 4.5K and Pete asked me to return the gauge to sample mode. As I did so, the level shot up to 99.9% and stayed there for several sample iterations. Pete put the pid loop back into automatic mode and the level seems to be stabilizing just like it was before the ESR crash. The combination of the inherent helium level gauge instability, and the limited travel of the top fill valve presented the failure mode. The fix is to temporarily increase allowed valve travel, and temporarily put the gauge into continuous mode until the temperatures are indicative of liquid helium presence.

A copy of this log entry has been emailed to: spiegel@jlab.org, fansler@jlab.org, folts@jlab.org, segal@jlab.org

Figure 1

readback_offset2

User name M. Stevens/TECH

Log entry time 17:10:39 on April 15, 2008

Entry number 232236