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 2.GQ Geiger Muller Counter
 GMC-300 counter CPM wrong.

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agi62 Posted - 08/03/2013 : 08:59:05
Hello, I apologize for the bad English,
I have recently purchased the GMC-300 and using it with his probe counts well the CPM but I has replaced his probe with a more sensitive and the calculation it is wrong.
The impulses that enter the GMC-300 are 150 CPMs but the counter visualizes more than 600 CPMs.
For the first 20 seconds after turn ON it visualizes well the impulses, it quickly increases later the number of the impulses.
I have verified the inpulses in entry to the GMC with digital scope and they are correct but the GMC visualizes a wrong number

It seems that:

1) the software mistakes the average for minute (CPM)

or

2) the hardware, over a certain number of impulses, reads badly.

Does the way to resolve the problem?

Thanks.
5   L A T E S T    R E P L I E S    (Newest First)
agi62 Posted - 08/06/2013 : 01:17:19
quote:
Originally posted by geny

I have same issue with a brand new GMC-300 V. 2.38 with original tube. When it go up to 70-80 CPM it displays about the double of correct amount of impulses and takes sometime even more that 15min to go back to background value...
Have you modified the board or software to fix the issue?


Hi,
I have not succeeded inserting the photos of the condenser, I send you to this link where I have explained everything:
h**p://radioactivity.forumcommunity.net/?t=50191071&st=60
agi62 Posted - 08/05/2013 : 04:15:58
quote:
Originally posted by geny

I have same issue with a brand new GMC-300 V. 2.38 with original tube. When it go up to 70-80 CPM it displays about the double of correct amount of impulses and takes sometime even more that 15min to go back to background value...
Have you modified the board or software to fix the issue?


Hello, I have added a 100pF ceramic condenser among the pin 7 and the pin 4 of the U6 (LM393).



Image Insert:

104.33�KB
geny Posted - 08/04/2013 : 16:34:07
I have same issue with a brand new GMC-300 V. 2.38 with original tube. When it go up to 70-80 CPM it displays about the double of correct amount of impulses and takes sometime even more that 15min to go back to background value...
Have you modified the board or software to fix the issue?
agi62 Posted - 08/04/2013 : 13:27:12
I have resolved the issue, the management of the input signal is not perfect, now works fine.
agi62 Posted - 08/04/2013 : 02:10:25
Is there someone who has verified this issue?

Thanks.

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