[Dsg-rtpc] [New Comment] MFC104 seems flaky

[beng at jlab.org]

Comments:
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 - by beng on Mon, 03/16/2020 - 16:58.

MFC104 Flow Rates - Sebastian, do you have a timestamp when you ran into this?

Also, which valves were you closing when you saw 200 sccm of flow?

The initial fill has always taken longer than subsequent ones, I'll leave that to the gas experts to explain.

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Logentry Text:
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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.

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