[Dsg-mvt] MVT gas pressure regulation issue

[Brian Eng]

Sorry for the multiple emails, last one before I find some dinner...

Looks like there is still MFC temperature alarms https://logbooks.jlab.org/entry/3560796

Maybe the heat tape needs to be adjusted lower again?

----- Original Message -----
> From: "Brian Eng" <beng at jlab.org>
> To: "Guillaume CHRISTIAENS" <guillaum at jlab.org>
> Cc: "DEFURNE Maxime" <Maxime.Defurne at cea.fr>, dsg-mvt at jlab.org, "Francesco Bossù" <fbossu at jlab.org>
> Sent: Saturday, April 14, 2018 8:16:29 PM
> Subject: Re: [Dsg-mvt] MVT gas pressure regulation issue

> By the way, there is a limit to this multiplier since we can't let the MFCs go
> below their minimum flow. It could probably be higher than the current 50%, but
> won't be able to be something like a factor of 10. I'd be surprised if we could
> get it to more than 2-3. FYI, the minimum value for the C4H10 MFCs is ~2 sccm.
> 
> Again, raising the demand flow would allow for a larger multiplier.
> 
> However, in theory you want the smallest possible one in order to make the
> changes in flow as infrequent as possible (which is why the DC is 20%).
> 
> ----- Original Message -----
>> From: "Brian Eng" <beng at jlab.org>
>> To: "Guillaume CHRISTIAENS" <guillaum at jlab.org>
>> Cc: "DEFURNE Maxime" <Maxime.Defurne at cea.fr>, dsg-mvt at jlab.org, "Francesco
>> Bossù" <fbossu at jlab.org>
>> Sent: Saturday, April 14, 2018 8:08:29 PM
>> Subject: Re: [Dsg-mvt] MVT gas pressure regulation issue
> 
>> 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
>> 
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