[dsg-hallb_gas] AHDC gas control

Thu Jan 16 09:18:45 EST 2025

Hi Whit,

That's what the Dwyer rep said when I called to ask what the difference between the psig and psia sensors were for that model.

I'll try again via email so we have some sort of paper trail.

Honestly this isn't the sensor I would have selected if we had known about the absolute pressure requirement, most of the gaseous detector systems we deal with in Hall B use differential ones, or maybe gauge. These sensors were selected well before that was changed later on in the development process.

________________________________
From: Armstrong, Whitney R. <warmstrong at anl.gov>
Sent: Thursday, January 16, 2025 9:11 AM
To: Brian Eng <beng at jlab.org>; dsg-hallb_gas at jlab.org <dsg-hallb_gas at jlab.org>
Cc: Whitney R. Armstrong <whit at jlab.org>
Subject: [EXTERNAL] Re: [dsg-hallb_gas] AHDC gas control

Hi Brian,

I am sorry but I do not think the pressure transducer is an absolute measurement.

Dwyer 626-06-GH-P1-E4-S

Can you please verify that it operates as you describe? Does it really have an absolute offset, because I am not seeing this anywhere in the manual/specs.

Thanks,
Whit

________________________________________
From: Brian Eng <beng at jlab.org>
Sent: Wednesday, January 15, 2025 5:01 PM
To: Armstrong, Whitney R.; dsg-hallb_gas at jlab.org
Cc: Whitney R. Armstrong
Subject: Re: [dsg-hallb_gas] AHDC gas control

Hi Whit, Answers are interleaved below in blue. From: Armstrong, Whitney R. <warmstrong@ anl. gov> Sent: Wednesday, January 15, 2025 5: 26 PM To: Brian Eng <beng@ jlab. org>; dsg-hallb_gas@ jlab. org <dsg-hallb_gas@ jlab. org> Cc: Whitney
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Hi Whit,

Answers are interleaved below in blue.

________________________________
From: Armstrong, Whitney R. <warmstrong at anl.gov>
Sent: Wednesday, January 15, 2025 5:26 PM
To: Brian Eng <beng at jlab.org>; dsg-hallb_gas at jlab.org <dsg-hallb_gas at jlab.org>
Cc: Whitney R. Armstrong <whit at jlab.org>
Subject: [EXTERNAL] Re: [dsg-hallb_gas] AHDC gas control

Thanks Brian.

Marc,

I have a few more questions.

1. I am still confused about this offset.
Is the transducer reporting an absolute pressure minus a fixed absolute offset? That seems odd to me.

Sort of, the only difference between a psig and psia output is what the zero reads at, either right at vacuum or 1 atm. This particular sensor the 0 psig output is equal to 14.7 psia. We don't use this offset anywhere in the software though, the only conversions done are to convert the 4-20 mA output to mbar (rather than the native psig output of the sensor).

You'd need a differential pressure sensor to have it referenced to a changing atmospheric pressure.

2. Also, where is the ambient pressure transducer located?

The ambient pressure is part of an existing Hall B setup and not done with any new hardware specific to ALERT. It is on the Forward Carriage Level 1, at the top of a rack there so roughly beam level.

3. What are the pid loop inputs for the automaitc mode? Average pressure, just one transducer or something else?

Just one transducer is used at a time, the PID input can be toggled between the two on the buffer tank. IIRC Bob added this for redundancy purposes.

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

________________________________
From: Brian Eng <beng at jlab.org>
Sent: Wednesday, January 15, 2025 4:14:13 PM
To: Armstrong, Whitney R. <warmstrong at anl.gov>
Subject: Fwd: [dsg-hallb_gas] AHDC gas control

This Message Is From an External Sender
This message came from outside your organization.

I’m not sure you got my previous email or not, so forwarding it directly to you.

Begin forwarded message:

From: Brian Eng via dsg-hallb_gas <dsg-hallb_gas at jlab.org>
Subject: Re: [dsg-hallb_gas] AHDC gas control
Date: January 15, 2025 at 1:28:10 PM EST
To: Marc Mcmullen via dsg-hallb_gas <dsg-hallb_gas at jlab.org>
Reply-To: Brian Eng <beng at jlab.org>

Hi Whit,

The control pressure is measured by the transmitter in psig, which is then converted to mbar in software. According to the manufacturer it has a fixed 14.7 psi (so ~1013.529 mbar) offset. If the set point is at 90 mbar it is really ~1103.529 mbar.

The ambient pressure sensor readout that is being displayed got stuck, rebooting it got the values updating again. The EPICS PV that ALERT is using is B_SYS_WEATHER_FC_L1:Press2 in case you wanted to monitor it directly/separately.

Let me know if there’s any other questions.

Brian

On Jan 15, 2025, at 12:34 PM, Marc Mcmullen via dsg-hallb_gas <dsg-hallb_gas at jlab.org> wrote:

Hi Bob, I’m out sick. So I’m forwarding this tho the group. Brian can probably look into it.

Also I looked and the input flow to MFC 308 is set to 20 sccm. Maybe change that to 167 sccm.

Marc

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________________________________
From: Bob Miller <rmiller at jlab.org>
Sent: Wednesday, January 15, 2025 11:20 AM
To: Armstrong, Whitney R. <warmstrong at anl.gov>; Marc Mcmullen <mcmullen at jlab.org>
Subject: Re: AHDC gas control

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>
Sent: Wednesday, January 15, 2025 10:44 AM
To: Bob Miller <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
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