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Procedure to move decarads
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CEDOG lock out
Introduction
The Decarad system was developed at JLab - it consists of 10 radiation detecting heads (geiger-mueller (GM) tubes) that connect (signal & HV cables) to a central box. That box has a board inside for changing the HV level and reading out the GM tube signals. The center box is connected to a digi port server via DB9 at box to RJ50 at the digi, which is then connected to the outside world via ethernet. The software uses the epics tool Stream with an asyn connection to the digi to send commands to the center box to read and write. The software is part of the RadiationMonitoring slac epics package.
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From the lower left corner of lcls home SC gun - X-ray/MISC+Global - select Decarad 1 or Decarad 2 to get the pydm display. It shows the read backs of the high voltage, the firmware number, a heartbeat, and the individual channel radiation read backs in approximate mr/hr. The GM tubes saturate with high radiation:
Screen shot of saturation curve from LND 714 datasheet - attached below.
Also , et al. It also has buttons to open a striptool for that decarad's dose rates and an archive viewer with the readbacks. Also on the pydm display is a place to type in the location of the system ("near CM35" for example) as well as positions for the individual heads ("near cavity 1", "between cavitiies 7 & 8", for example). These typed in values as well as the desired high voltage setting is saved across IOC reboots. All numeric values except for the heartbeat and firmware number are archived.
Showing path to get main decarad display, strip tool, and archive viewer.
Main decarad display.
n.b. The GM tubes saturate with high radiation:
Screen shot of saturation curve from LND 714 datasheet - attached below.
The radiation read back PV names are RADM:The radiation read back PV names are RADM:SYS0:x00:GAMMA_DOSE_RATE, where x is 1 or 2.
About the software
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The decarads are talked to through a DB9 connector connected to a Digi Portserver. The software uses EPICS ASYN and Stream Device to send the commands to set the HV, read back the measurements, etc. The software is part of the RadiationMonitoring slac epics package. The source code can be reached from a development machine (currently afs): cd $EPICS_IOC_TOP/RadiationMonitoring. The database code is in RadiationMonitoringApp/Db/common in three files: decaradChannel.template, decaradCommon.template, decarad.substitutions. The file with the read/write commands is RadiationMonitoring/protocols/decarad.proto. The startup files are in iocBoot/sioc-sys0-rm01. The ioc status & control can be seen from LCLShome, SC gun, Network/Global under RadiationMonitoring sioc-sys0-rm01. The IP addresses are ts-sys0-nw01 and -nw02.
The database files have the PVs divided by per-head and per-system:
We have two decarad systems. Each consists of 10 small Geiger-Mueller (GM) radiation detecting heads that are connected (signal & high voltage (HV)) to a central unit which has some brains to control the HV level and read out the measured dose rates. The plan is to mount these to two frames that will be positioned near cryomodules during RF commissioning to measure radiation. The systems will be moved every day or two as we commission all cavities. The systems were designed and built at JLab and used for many years. The decarads are talked to through a DB9 connector connected to a Digi Portserver. The software uses EPICS ASYN and Stream Device to send the commands to set the HV, read back the measurements, etc. The software is part of the RadiationMonitoring slac epics package. The proposed software is currently in afs:
~jnelson/sandbox/RadiationMonitoring/RadiationMonitoring-git/RadiationMonitoringApp/Db/common:
decaradChannel.template - records associated with each GM head
decaradCommon.template - records associated with the system
decarad.substitutions - substitution file for templates
The proposed ioc name is sioc-sys0-rm01.
In ~jnelson/sandbox/RadiationMonitoring/RadiationMonitoring-git/iocBoot/sioc-sys0-rm01 is the st.cmd file.
For archiving I made:
...sandbox...RadiationMonitoringApp/srcArchive/common/For archiving:
RadiationMonitoringApp/srcArchive/common/decaradChannel.tpl-arch and decaradCommon.tpl-arch
...sandbox...RadiationMonitoringApp/srcArchive/lcls/sioc-sys0-rm01.sub-arch
Below is a description of the PVs with proposed names
Proposed PV names:
PV names:
| PV PV Name | Purpose | Save/restore | Archive |
|---|---|---|---|
| $(P):DEV_FW | read firmware number | ||
| $(P):HEARTBEAT | read heartbeat | 10s | |
| $(P):HVSTATUS | read status of high voltage | 10s | |
| $(P):CHAS_TEMP | read temperature of chassis | 10s | |
| $(P):HVMON | high voltage reading (V) | 10s | |
| $(P):HVSETPTHVCTRL | high voltage setting (V)on/off 0 = on, 1 =off | yes | 10s |
| $(P):LOCATION | String to hold a description of the rack position | yes | |
| $(P):nn:GAMMA_DOSE_RATE | read back of dose from GM tube nn (01-10) in mR/hr (close enough, saturation curve starts to roll over about 10R/hr - see plot below) | 1s | |
| $(P):nn:POSITIONPOSN | string to hold a description of the position of GM tube number nn | yes | |
| $(P):SEQ | sequence to readout the PVs at 1 Hz. The SEQ record has a delay of 0.06 seconds between sending 1 to each PV's PROC field so commands don't collide in the cable |
There are two sets of decarads (10 heads + central unit) so the PVs listed above are doubled and differentiated by $(P).
Suggested $(P) = RADM:SYS0:100 or RADM:SYS0:200 for the two systems.< End section for Naming Czars - thank you for your help! >systems.
How to set the HV
From: Larry King <king@jlab.org>
Sent: Wednesday, March 9, 2022 12:49
To: Nelson, Janice L. <jnelson@slac.stanford.edu>
Subject: RE: decarad hv settings
Hi there, Janice,
No bother at all, I’m happy to tell you what I know about the HV setting.
I’m assuming you’re using the same G-M tube as the original design. The data sheet for the LND714 tube says the operating range is 450-650V, and they’ll work as low as 380V. Setting the HV is really just a balance between longevity and sensitivity. The tubes are only good for a limited number of interactions, so the higher the voltage, the more interactions and the shorter the lifespan.
When we first rolled the DecaRads out in 2010, we picked 650V for max sensitivity. After a few years of replacing tubes, we opted for a lower bias of 500V. While the cost of the tubes is not exorbitant, the downtime for tube replacement can add up. Since the 10 tubes share a common HVPS, when one tube dies it often affects the response of the remaining tubes. Sometimes the dead tubes just stop responding, but other times it may also present a significant load on the small HVPS and drag down the HV for all.
The HV for each chassis is set with a small pot on the front panel, and a DMM on the 1000:1 BNC connector. There’s no feedback in the bias, so when the heads are loaded down by radiation or tube death, the HV droops. Also, be extremely careful tweaking the pot. It’s a very small, surface mounted potentiometer that is easily popped off of the PCB with too much insertion force with the tweaker, OR just by rotating the tweaker too forcefully, if the pot and the hole in the chassis are off-axis. Please pass this message along to whomever might be doing this adjustment. I’d recommend taping up the hole after adjustment, just to discourage the casual tweaker. You know the type.
Good to hear from you. Just let me know if I can help.
Regards,
Larry
To Do:
- Order from
TECO - 80/20 - Get db9 cables from Doug
- Test digis in tunnel
- if cables ok, roll up other cable on reelIf not, get more cables
- Test a system in the tunnelstart softioc
- See what values HVSTAT getsRelease display
- Test software: displays, save/restore, archivingCable tags on cables
- Put caps on framesMake DB9/RJ50 cables
Cable Connection
Notes on cable connection (from email 8/12/21)
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