[Hallb-engineering] DVCS LHe reservoir filling

David Kashy kashy at jlab.org
Fri Oct 2 13:18:56 EDT 2009

Hi All,
I spent this morning it the hall looking at the DVCS Solenoid and 
helping with other stuff.
Thanks for the invite Doug!

I found that the level probe is working quite well and should not be a 
problem for operations.
The cryogenics for the solenoid seem good. Currently it is running with 
the liquid helium level slightly above the set point of 70%.
This is not a problem.
The current lead flow set point is 30 liters/minute. This is lower than 
we needed to run in the past and we may need to increase it when we 
energize the magnet.
Last time I believe we ran as high as 60 l/m .

While looking at the Solenoid Controls I found the MSS to be in Default.
Krister and I started to trouble shoot. We found one problem and then 
Krister found a second and both were fixed.
When I left the Hall there was one more problem that Krister was still 
working on.

Before we ramp up the magnet we must remember to turn the FV-MSS switch 
on the console from 1 to 0.

Good job over this down to everyone!!

Steve Christo wrote:
> 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.
> Steve
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