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 2.GQ Geiger Muller Counter
 Unusual spikes in 600+ at high CPM (bug?)
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kotarak

USA
19 Posts

Posted - 05/22/2020 :  15:45:59  Show Profile  Reply with Quote
I was just checking some of my minerals and I noticed a problem with my GMC-600+ when checking a few higher activity gummite crystals.

The normal (usual) reading for this specimen was around

235 156 CPM
671.87 uSv/h (67.19 mR/h)
@ 1/2" from the mineral

occasionally though, the reading will jump drastically for a few moments
to a much higher reading

392 580 CPM
1121.66 uSv/h (112.17 mR/h)

This high count event will last a second or two and then it will go back to the normal reading of around 600-700 uSv/h.
I took these numbers from pictures I was able to capture and for whatever reason I can't upload in the forum - I get an error during upload.
This is not that high of a count to saturate the tube but it happened a few time already.
Is it problem with the math / calculation or something is going on with the hardware - I cant imagine to see an increase of 150 000 CPM just randomly out of the blue...ill try to run the GMC-600+ side-by-side with my Gamma Scout but the GS is using LND712 so it is not going to be apples to apples comparison.


Reply #1

EmfDev

1243 Posts

Posted - 05/22/2020 :  16:51:16  Show Profile  Reply with Quote
Hi kotarak,

It could be because it is using "Dynamic" CPM estimation. If the device detects a high change in CPS, it will change the calculation based on past few seconds until it becomes stable. Looks like it detected 1 second of high pulse that is why it calculated the CPM with that data as higher contribution to the total CPM. Usually when this happens, you can see the +- percent error at the top to become higher. You can turn off this feature in the menu by changing "Dynamic" to "60 seconds". This means that whatever CPM it gets within 60 seconds will be shown. But the downside is you need to wait 60 seconds to get a full CPM reading.
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Reply #2

kotarak

USA
19 Posts

Posted - 05/22/2020 :  18:06:25  Show Profile  Reply with Quote
Hi EmfDev,
Thank you for pointing out the dynamic estimation feature. I will turn it off.
I just checked the pictures and indeed it was +/-5% when showing the "normal" reading and +/-30% during the high reading display.
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Reply #3

kotarak

USA
19 Posts

Posted - 05/23/2020 :  08:22:09  Show Profile  Reply with Quote
EmfDev,
Thank you for your explanation - I get exactly what was happening!

Out of curiosity, in Dynamic mode estimation, what is the granularity of the time periods over which the rate is averaged?

Is the averaging period actively adjusted (expanded) up to a minute or it uses fixed "chunks" of time (how many seconds?) over which the averaging is calculated?

Best regards,
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Reply #4

EmfDev

1243 Posts

Posted - 05/26/2020 :  09:29:05  Show Profile  Reply with Quote
It starts from 3 seconds and steadily using 5 - 10 - 15 - 20 - 30 - 60 seconds as long as readings are stable. And will trigger it if CPS has 50% change than previous 1 or 2 at high CPM.
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Reply #5

kotarak

USA
19 Posts

Posted - 05/26/2020 :  11:04:24  Show Profile  Reply with Quote
quote:
Originally posted by EmfDev

It starts from 3 seconds and steadily using 5 - 10 - 15 - 20 - 30 - 60 seconds as long as readings are stable. And will trigger it if CPS has 50% change than previous 1 or 2 at high CPM.


Thank you so much! Is this averaging occurs relative to the actual RTC of the counter? Meaning I get an estimation on the 3rd second after each minute of the clock, then on 5th , 10 sec... etc seconds past the clock minute or it is relative to some other event like switching to a specific measuring mode?
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Reply #6

EmfDev

1243 Posts

Posted - 05/26/2020 :  12:02:16  Show Profile  Reply with Quote
A full minute stable reading is the sum of the last 60 second CPS or counts per second. If it detects a significant change on the CPS, it will first estimate CPM with only the past 3 seconds of reading so CPM = 20*sum of last 3. as long as CPS is stable the estimation window will increase until it reaches 60 seconds.
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