[Hallb-engineering] DVCS LHe reservoir filling
christo at jlab.org
Fri Oct 2 06:53:06 EDT 2009
Cooling the DVCS solenoid problem.
Background: EV8215 (the DVCS LHe supply valve from the Buffer Dewar) was
set to manual for the last 2 days at 46% which yielded a fairly uniform
temperature fall rate of 10K/hr. The level probe for LL8310 (DVCS LHe
reservoir) was changed before cooling down because the old probe was
giving a false reading before cool down. Because the new probe has a
smaller diameter at the Goddard fitting, it was supplied with an adapter
that raised the probe approx. 1 cm. above the old level probe. Krister
calibrated the readout using the resistance value labeled on the probe.
The DVCS LHe reservoir began filling at about 18:28 yesterday evening. I
expected the fill to be slow and steady, taking at least several hours
with EV8215 set to 46%. Instead, it filled from indicated level of 0 to
approx. 70% in less than 3 minutes and filled from 70% to 77% in the
next 2 to 3 minutes. 77% was the maximum value achieved. When I
accidentally increased the flow rate this morning, (using incorrect
control signal on the PID loop for EV8215) the reservoir was over
filling and the level indication remained at 77%. This can be explained
by the height offset of the new probe and can easily be corrected with
an offset in readout.
The rapid indicated filling, however, makes me suspicious. I'm worried
that "0" might not really be "0". It could be a problem with the probe,
the span, or the calibration. We'll need to check into this.
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