[Dsg-mvt] MVT gas pressure regulation issue

[Brian Eng]

Hi Guillaume,

Sorry for the late reply, I saw the email, but didn't have access to a computer until now.

The current factors are to reduce/raise the flow by 35% of the demand value (see this entry: https://logbooks.jlab.org/entry/3544160)

I've put them back to 50%, even though that value seemed to work fine for quite a while (since 4/6).

The mixing system is doing what it is supposed to, the 20 psi number was for safety and it should set the multiplier to 0 to stop flow.
We can raise this number as well if your system can handle it, but it shouldn't ever get that high to begin with.

I see mix 2 is over 15 psi as well, which means it has the same issue, but just isn't effected as much.
I suspect this might be because the temperature inside the MFC enclosure is 95F, which is much higher than I recall seeing in the past.

If the pressure is still is an issue even with the increased multiplier, one of the things you can try doing is raising the flow on the MVT/FTT doing so will make the difference between the demand flow and mixing flow higher which should make the changes faster.

----- Original Message -----
> From: "Guillaume CHRISTIAENS" <guillaum at jlab.org>
> To: "Brian Eng" <beng at jlab.org>, "Marc McMullen" <mcmullen at jlab.org>
> Cc: "Francesco Bossù" <fbossu at jlab.org>, "DEFURNE Maxime" <Maxime.Defurne at cea.fr>
> Sent: Saturday, April 14, 2018 5:22:11 PM
> Subject: MVT gas pressure regulation issue

> Dear all,
> 
> Sorry if you received a duplicate message about this subject. I had an
> issue with my first mail and wasn't sure it was sent.
> 
> So we have an issue with pressure regulation for mix 1.
> Pressure reached 20 psi and don't want to decrease, it oscillate between
> 19.99 where flows are reduced (by a factor 2 I think) and 20.00 where
> flows are 0.
> However it seems that the flows scaled by this factor 2 is not enough to
> decrease the flows today, I guess because of temperature changes.
> 
> Since factor 2 doesn't seem to be enough, do you know how we can change
> this factor to 4, 5 or even maybe 10 ? Can we do it remotely ?
> 
> Thanks
> 
> Guillaume