[dsg-hallb_gas] AHDC gas control

[Brian Eng]

Hi Whit,

Since Marc is out I’ll try to answer these as best as I can, which is why it’s also CC'd to our group’s gas mailing list in case I got anything grossly wrong.

That particular ambient pressure (and temperature) sensor is located on the Forward Carriage Level 1, at the top of rack C2-10, which is roughly at beam height at one of the most beam left racks.

I thought there was a document describing the system; maybe Bob has something he can share? Roughly pressure in the DC is controlled by PID based on the pressure in the buffer tank. There are two pressure sensors (both 0-5 psig) that can be selected from as the process variable, the PID in turn controls the flow set point to the exhaust MFC. When more pressure is needed flow through the exhaust is reduced, when less pressure is needed flow through the exhaust is raised.

One thing to keep in mind if you’re not getting enough pressure is that the supply flow to the DC must be high enough to account for any possible leaks/losses. If that isn’t high enough the PID will set the exhaust to 0 but the pressure won’t get to the set point.

Hope that helps.

On Jan 15, 2025, at 4:11 PM, Marc Mcmullen <mcmullen at jlab.org> wrote:



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________________________________
From: Armstrong, Whitney R. <warmstrong at anl.gov<mailto:warmstrong at anl.gov>>
Sent: Wednesday, January 15, 2025 3:02:29 PM
To: Bob Miller <rmiller at jlab.org<mailto:rmiller at jlab.org>>; Marc Mcmullen <mcmullen at jlab.org<mailto:mcmullen at jlab.org>>
Subject: [EXTERNAL] Re: AHDC gas control

Hi Marc,

I see the ambient pressure is now reading values consistent with the weather. Where is this transducer located?

Could you please describe the pressure measurements and how they are used to maintain the gas pressure in the drift chamber?

Thanks,
Whit

Whitney Armstrong
Assistant Physicist
Physics Division
Building 203

Argonne National Laboratory
9700 S. Cass Ave. | Argonne, IL 60439
630-252-5112 | 717-341-1080 mobile
warmstrong at anl.gov<mailto:warmstrong at anl.gov>
________________________________
From: Bob Miller <rmiller at jlab.org<mailto:rmiller at jlab.org>>
Sent: Wednesday, January 15, 2025 11:20:34 AM
To: Armstrong, Whitney R. <warmstrong at anl.gov<mailto:warmstrong at anl.gov>>; Marc Mcmullen <mcmullen at jlab.org<mailto:mcmullen at jlab.org>>
Subject: Re: AHDC gas control

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Hi Whitney,

I will refer this question to Marc, as he wrote the controls.



Bob Miller
Hall B Lead Engineer
(757) 822-9586
________________________________
From: Armstrong, Whitney R. <warmstrong at anl.gov<mailto:warmstrong at anl.gov>>
Sent: Wednesday, January 15, 2025 10:44 AM
To: Bob Miller <rmiller at jlab.org<mailto:rmiller at jlab.org>>
Subject: [EXTERNAL] AHDC gas control

Hi Bob,

I have a question about the gas control system. When the alert gas set point is set to 90 mbar, what is that relative to in order to provide stable absolute pressure?

Also, the ambient pressure readout appears to not change and is at a value of 1017.54.

Thanks,
Whit

Whitney Armstrong
Assistant Physicist
Physics Division
Building 203

Argonne National Laboratory
9700 S. Cass Ave. | Argonne, IL 60439
630-252-5112 | 717-341-1080 mobile
warmstrong at anl.gov<mailto:warmstrong at anl.gov>

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