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Hi Brian,
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<div class="">thanks for responding. I personally believe we have seen this problem pretty much from the beginning, but it has gotten worse. I don’t think there is any gas dynamics reason why the first fill should take longer; in any case, sometimes it’s the
2nd fill as well. For example, see the following 2 purge cycles:</div>
<div class=""><a href="https://logbooks.jlab.org/entry/3805040" class="">https://logbooks.jlab.org/entry/3805040</a></div>
<div class="">(This one was this morning purging with nitrogen, but it doesn’t depend on the gas)</div>
<div class=""><a href="https://logbooks.jlab.org/entry/3805043" class="">https://logbooks.jlab.org/entry/3805043</a></div>
<div class="">This one was yesterday purging with deuterium. As you can see, in this case the first TWO refills took “forever” (16 min) while the third one was normal (about 4 minutes). NOTHING changed in between - SVBT100 was open, the D2 gas pressure was
steady, etc.. Obviously, we can survive with this, but if in the worst case we have to wait for 3 of these long fill cycles, we are wasting close to 1 hour of beam (or whatever else we need the purge for). Also, if the flow rate readback is too large, we can
trigger automatic shutdown (target empty) in auto mode, so we cannot use auto mode for purging anymore (at least we feel uneasy). </div>
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<div class="">The flow readback I saw at 200 sccm was when I had both SVBT100 and SVBT102 closed, as well as SVBT108. So there really shouldn’t have been any way for flow to occur. More generally, the flowrate readback often reads 200 sccm throughout the whole
fill cycle, although it should go down as the target gets close to the fill pressure. Of course, it’s a “flaky” problem, in the sense that sometimes the feedback is perfectly fine - e.g., right now (with no target connected and all valves closed it does read
0 sccm).</div>
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<div class="">If there is a way to check out MFC104 (or swap it out) over the next 2 days, that might help us save some precious beam time going forward. Of course, we do want to avoid that we can’t start the run back up on Friday because the gas panel is not
fully ready for operations. Please let me know if you think there is something we can do to fix this?</div>
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<div class="">Thank you so much - Sebastian<br class="">
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<div class="">On Mar 16, 2020, at 5:00 PM, <a href="mailto:beng@jlab.org" class="">
beng@jlab.org</a> wrote:</div>
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<h1 class="node-title" style="font-size: 1.6em;"><a href="https://logbooks.jlab.org/entry/3803565" rel="bookmark" style="text-decoration: none;" class="">MFC104 seems flaky</a></h1>
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Lognumber<span class="Apple-converted-space"> </span><a href="https://logbooks.jlab.org/entry/3803565" class="lognumber" data-lognumber="3803565" style="text-decoration: none;">3803565</a>. Submitted by<span class="Apple-converted-space"> </span><a href="https://logbooks.jlab.org/user/kuhn" style="text-decoration: none;" class="">kuhn</a><span class="Apple-converted-space"> </span>on<span class="Apple-converted-space"> </span><time datetime="2020-03-13T18:47:04-0400" pubdate="pubdate" class=""><a href="https://logbooks.jlab.org/entries?start_date=1584136024&end_date=1584143224&book=HBRTPC" style="text-decoration: none;" class="">Fri,
03/13/2020 - 18:47</a></time>.<span class="Apple-converted-space"> </span></div>
<div style="font-size: 9.1875px; margin: 0.1em 0px;" class="">Last updated on<span class="Apple-converted-space"> </span><time datetime="2020-03-13T18:51:23-0400" pubdate="pubdate" class="">Fri, 03/13/2020 - 18:51</time></div>
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<div class="fieldset-wrapper"><a href="https://logbooks.jlab.org/pr/edit/876536" class="cool-class" id="prid" style="text-decoration: none;">Update this Record...</a><section class="field-name-needs-attention view-mode-full clearfix field-label-inline field-type-text field">
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<div class="field-item even">Hall B > Hall B Detectors > Hall B CLAS12 Detector > CLAS12 Gas</div>
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Responsible Group: </h2>
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<div class="ctools-collapsible-content"><a id="comment-28152" style="text-decoration: none;" class=""></a><article class="comment-new first comment odd clearfix" style="padding-left: 10px; background-color: rgb(238, 238, 238);"><header class="comment-header">
<h3 class="comment-title"><a href="https://logbooks.jlab.org/comment/28152#comment-28152" rel="bookmark" style="text-decoration: none;" class="">MFC104 Flow Rates</a></h3>
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by<span class="Apple-converted-space"> </span><a href="https://logbooks.jlab.org/user/beng" title="View user profile." class="username" style="text-decoration: none;">beng</a><span class="Apple-converted-space"> </span>on<span class="Apple-converted-space"> </span><time datetime="2020-03-16T16:58:28-0400" pubdate="pubdate" class="">Mon,
03/16/2020 - 16:58</time></div>
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<div style="font-size: 9.1875px; margin: 0.1em 0px;" class="">Sebastian, do you have a timestamp when you ran into this?</div>
<div style="font-size: 9.1875px; margin: 0.1em 0px;" class="">Also, which valves were you closing when you saw 200 sccm of flow?</div>
<div style="font-size: 9.1875px; margin: 0.1em 0px;" class="">The initial fill has always taken longer than subsequent ones, I'll leave that to the gas experts to explain.</div>
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kuhn</td>
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<p class="">We continue seeing strange behavior when we first fill the target with a new gas. The rise in pressure is VERY slow, although the MFC104 readback claims 200 ccm. Subsequent fills go much faster, with no change in the readback from MFC104. In fact,
I have observed MFC104 Flow reading 200 ccm WITH THE VALVES CLOSED! During the second fill, the readback becomes more reasonable, going to lower values as the target fills up (6 ccm with valves closed). Of course if the MFC reads full flow, the valve doesn't
open as much... This may also be the root cause for our continuing troubles taking the system into auto mode - as long as MFC104 reads a high flow rate, the fail-safe logic will assume there is a leak and shut all inlet valves. For now, I continue in manual
mode.</p>
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