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 2.GQ Geiger Muller Counter
 GMC-320 plus V4 and SBM-20 (ΡΑΜ-20)
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i80386

15 Posts

Posted - 08/03/2019 :  08:58:00  Show Profile  Reply with Quote
Hello, is it possible to install the SBM-20 tube in the latest revision of the GMC-320+ V4. Or maybe the battery holder will be a problem?
Reply #1

EmfDev

2139 Posts

Posted - 08/05/2019 :  09:33:13  Show Profile  Reply with Quote
Hi i80386,

quote:

...the SBM-20 tube is a little longer than the M4011 and the clips to hold it to the PCB
is too close to each other to fit it. You have to do some DIY stuff to fit it inside. The case is large enough,
but you need to move 1 of the clips inside.



you can read more about SBM-20 in these threads.
https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4571&SearchTerms=sbm

https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=3654&SearchTerms=sbm
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Reply #2

PKIDelirium

USA
14 Posts

Posted - 08/06/2019 :  12:57:23  Show Profile  Reply with Quote
This is an older type (non-plus) 300E, but it shows the steps involved with swapping the tube: https://www.youtube.com/watch?v=tVNozQmwsGI

I believe the 320+ uses the same main board as the 300E+ (newer version than seen in the video, but similar except for different battery size), and I've also seen a 300E+ with an SBM-20 conversion so the battery holder for the AA-size cell isn't a problem.
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Reply #3

Matt

USA
3 Posts

Posted - 03/30/2023 :  16:01:26  Show Profile  Reply with Quote
Does anyone here know the sbm-20 tube cal settings?

Matt jack
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Reply #4

ullix

Germany
1107 Posts

Posted - 03/30/2023 :  22:24:56  Show Profile  Reply with Quote
See GeigerLog manual, chapter Calibration.
https://sourceforge.net/projects/geigerlog/files/
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Reply #5

Matt

USA
3 Posts

Posted - 04/01/2023 :  10:23:17  Show Profile  Reply with Quote
Thank you so much ullix . I got to read the calibration section but I could not understand how to convert to put in the values in the 320 plus and what numbers to use?

Matt jack

Edited by - Matt on 04/01/2023 11:11:53
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Reply #6

ullix

Germany
1107 Posts

Posted - 04/02/2023 :  01:04:46  Show Profile  Reply with Quote
Since you read the chapter, you will have realized that there is no point to change the calibration, since it is "the other way round": The GMC counter uses the average as the two specific SBM20 calibrations as its own universal calibration! Without having done a calibration, as there has never been one presented.

But if you have good reason to set a new calibration, then start GeigerLog and look at the "Set GMC Configuration" dialog:



This one is for a GMC-300S. It shows 3 calibration points, and all three are needed by the firmware, although all 3 result in the exact same sensitivity of 161.538 in units of CPM / (uSv/h).

Assuming you now want a sensitivity of 200. Don't change the CPM values (needed for some odd function in the firmware) and calculate all three CPM / Sensitivity: e.g. for the first: 105 / 200 = 0.525, and put it into the 3 fields for uSv/h:



Now you have a sensitivity of 200 CPM/(uSv/h), click the ok button, and you are done, the counter is set to that new sensitivity!

Note that these values are used ONLY inside the counter! GeigerLog ignores those settings, and uses whatever you have set it to. And you can change it at any time, back and forth.




Edited by - ullix on 04/02/2023 01:38:14
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Reply #7

ullix

Germany
1107 Posts

Posted - 10/08/2023 :  23:46:12  Show Profile  Reply with Quote
Then I suggest to install GeigerLog and use the dialogs as shown in Reply#6 to enter your numbers, then click the ok button, and it will be uploaded to the counter.

But there is no need to modify the default calibration, as the default calibration of a GMC-3XX counter is actually taken as the average of the two calibration values known for the SBM20; see the GeigerLog manual.


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