[Dsg-mvt] MVT gas pressure regulation issue

[Brian Eng]

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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