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 2.GQ Geiger Muller Counter
 [GMC 600+] What CPM per uSv/h conversion?
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bc10

7 Posts

Posted - 08/14/2019 :  12:02:45  Show Profile  Reply with Quote
New owner of a GMC 600+ here.

I don't have a standardized source to test the accuracy of the device's measurements right now. I'm wondering what your CPM per uSv/hr conversion is?

Mine is roughly set at 350 CPM per uSv/h.

Is that the default setting? Are each unit individually calibrated at the factory or do they use the same conversion for the same model? Is this conversion factor in line with other products that also use the LND 7317 detector?

My current background radiation is reading roughly 50 CPM indoors. Seems kinda high in activity but it could be OK if the detector is more sensitive.

Also, are any of you guys using makeshift methods to protect the exposed detector when you're not attempting to measure alpha? In case dust settles on the detector's surface. I'm currently using some 3M painters tape to cover up the opening.

Edited by - bc10 on 08/14/2019 12:28:12
Reply #1

Geo-Johnny

Austria
154 Posts

Posted - 08/14/2019 :  12:27:36  Show Profile  Reply with Quote
quote:
Originally posted by bc10

Mine is roughly set at 350 CPM per uSv/h.



Conversation 350 could be okay.
Look at this: https://sites.google.com/site/diygeigercounter/technical/gm-tubes-supported

Geiger Counters: GMC320+V5 & GMC500+
Geiger Tubes: M4011; SI-3BG; SBT-9; LND712; SBM-20

Edited by - Geo-Johnny on 08/14/2019 12:29:01
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Reply #2

bc10

7 Posts

Posted - 08/14/2019 :  12:34:45  Show Profile  Reply with Quote
quote:
Originally posted by Geo-Johnny

quote:
Originally posted by bc10

Mine is roughly set at 350 CPM per uSv/h.



Conversation 350 could be okay.
Look at this: https://sites.google.com/site/diygeigercounter/technical/gm-tubes-supported



Thanks. Yeah I was just taking a look at that blog too. It seems the Inspector EXP that also uses the LND 7317 uses 330 conversion factor according to the author.
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Reply #3

EmfDev

908 Posts

Posted - 08/14/2019 :  12:41:50  Show Profile  Reply with Quote
You can check this thread by stargazer 40

https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=5554
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Reply #4

bc10

7 Posts

Posted - 08/14/2019 :  12:54:42  Show Profile  Reply with Quote
quote:
Originally posted by EmfDev

You can check this thread by stargazer 40

https://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=5554



Thanks! That's very interesting raw data. His device is also around 350 conversion for the LND 7317.

This leads me to wonder if there is a setting for GMCmaps to show converted dose measurements instead of raw CPM data? Most people don't have the more sensitive models when uploading their readings to the crowd sourced map so can't compare apples to apples with people in my area.
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Reply #5

EmfDev

908 Posts

Posted - 08/14/2019 :  13:00:25  Show Profile  Reply with Quote
The pins also display the uSv/h beside the CPM in the map.
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Reply #6

bc10

7 Posts

Posted - 08/14/2019 :  13:29:31  Show Profile  Reply with Quote
quote:
Originally posted by EmfDev

The pins also display the uSv/h beside the CPM in the map.

The pins in my web browser only seem to show the raw CPM number. Some pins show uSv/h but I'd have to click on a pin to see it.

Edited by - bc10 on 08/14/2019 13:29:44
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Reply #7

EmfDev

908 Posts

Posted - 08/14/2019 :  13:33:05  Show Profile  Reply with Quote
Oh that's true. It only shows CPM when you don't click on the pins. And option to change it to dose isn't there.
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Reply #8

paul

United Kingdom
44 Posts

Posted - 08/14/2019 :  13:58:42  Show Profile  Reply with Quote
and it would be very nice and a bit more ergonomic if there were such
an option.
would make it easier to see ,as each tube seems to have a different
conversion rate.
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Reply #9

Stargazer 40

USA
346 Posts

Posted - 08/14/2019 :  18:28:56  Show Profile  Reply with Quote
The LND spec sheet for the 7317 shows 350CPM/uSv for the specified recommended voltage. GMC may be running a little hotter than that for GM tube voltage so 330 might give a better match for some counters. I'll stay with 350 for my 600+. It's also what Mazur uses in the 9000 meter.

I'll be running some new calibration tests and posting results shortly. Waiting on some firmware upgrades. Some really exciting things going on with GQ stability as counts go high. Should once again take GQ up another big notch for their flagship meter.

Stargazer 40
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