[Dsg-mvt] MVT Mixing System Testing

[Marc McMullen]

Hi Amrit,

On 12/6 the Saclay MVT gas controls started with demanding mixed gas 
from the Hall B gas controls, which was setup in automatic mode. This 
started the flow of Ar and C4H10 from the MVT mixing system. That 
evening MVT staff observed fluctuations in flow from the C4H10 mass flow 
controllers. We checked it out  and noticed fluctuations in C4H10 
supply, and odd behavior from the mfcs such as: reporting significant 
flow, with the internal valve closed. extremely slow response to  change 
in flow commands.  These issues have only been observed with the C4H10 
mfcs. We spent most of the day yesterday troubleshooting the Mix 2 C4H10 
mfc. The last part of the day we operated the mfc using the software 
provided by MKS and performed the "zeroing" procedure a couple of times 
to correct a flow offset. During this part of the procedure the gas 
supply is mechanically valved off and the mfc is isolated as much as the 
valve panel will allow. Generally, this produces a small flow value (0, 
+/-  < 1 unit), close to zero. As I observed the flow, I noted that the 
flow was all over the place for a long time before it settled at a point 
where I thought it was ready to complete the procedure. However once I 
opened the manual gas valve the offset returned. This morning I noted 
that it was back in the "normal" range, so that offset flow number must 
take a while to bleed off.

In any case, we will start a rigorous testing procedure on the spare, 
using a normal gas type (maybe compressed air) in a controlled 
environment on Monday. Once we are sure that it works, we will have it 
installed and perform those tests on the mixing system, first using 
Argon and then finally C4H10. I should have a full report completed for 
the next DSG status meeting on Wednesday.

We have informed the MVT group to use the 2 premix bottles they have on 
the target gas pad for data taking. We have ordered 10 bottles of  
premix, and it has been signed and ordered by procurement.

-- 
Marc McMullen
Detector Support Group
757-269-7738