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 2.GQ Geiger Muller Counter
 GMC300e Plus ,Problem. unusually hIgh CPM ,
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Ways

United Kingdom
1 Posts

Posted - 06/21/2020 :  14:08:45  Show Profile  Reply with Quote
Hi ,

For the past 10 months or so my GMC300e has been plugged into my PC working away and occasionally uploading data to GMCMAP.
A couple of months ago it started making a hideous beeping noise and i noticed the CPM count was very high (230 ish , usually 40 ish) i guess the beeping was the CPM alarm, i have other Geiger counters and they where not showing any higher than usual reading so i figure its a fault.

I did a factory reset and it seemed ok, but it has since been reading extremely low for a while and now its back to extremely high.

I am baffled, the factory reset didnt help , i have moved it to other parts of my house and surroundings but same high readings.

If i introduce it to a gas mantle it goes mental as it should, any ideas on how i can trouble shoot this?

Thanks
Reply #1

EmfDev

1243 Posts

Posted - 06/22/2020 :  09:20:56  Show Profile  Reply with Quote
Hi Ways, can you try to remove the back cover and just reconnect the tube? maybe it is just connection issues.
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Reply #2

ChrisP

Austria
6 Posts

Posted - 06/28/2020 :  13:02:09  Show Profile  Reply with Quote
Hi,

I have exactly the same problem with my 500+. It’s connected 24/7 via usb to my pc and worked without a problem for about 9 months (bought it 2019/09). About three weeks ago the high cpm alarm went off in the middle of the night. After resetting the device it showed normal cpm (around 10-20) but after a few minutes it went back to 30-60 cpm. The current average for the last 5 days is 30cpm with max 58. this seems about double the real value. Also it sounds as if counts get „double counted“ (two very quick counts instead of one).
I have already check the connection of the tubes - it seems ok.

Any advice?

Christian
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Reply #3

EmfDev

1243 Posts

Posted - 06/29/2020 :  09:07:07  Show Profile  Reply with Quote
ChrisP, can you check tube 2 CPM by turning on tube 1 and 2 CPM display in the tube settings? check to see what is the CPM of tube 2 when the CPM is 30-60. If tube 2 is < 3 and mainly tube 1, try to lower down the voltage of tube 1 by 2-3%.
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Reply #4

ChrisP

Austria
6 Posts

Posted - 07/02/2020 :  10:19:18  Show Profile  Reply with Quote
EmfDev thanks for your advise! I turnend on tube 1 & 2 CPM and it shows 0 CPM for tube 2 and from 30-60 CPM for tube one. after that I reduced the voltage setting for tube one from 44% to 42%. That reduced the avg cpm to about 27CPM after 24h. A further reduction to 40% reduced 24h avg cpm to 25.

This looks like some kind of defect with tube 1 to me.

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Reply #5

EmfDev

1243 Posts

Posted - 07/02/2020 :  10:32:17  Show Profile  Reply with Quote
Hi ChrisP, looks like the voltage is shifted and made the CPM increase. Try to adjust the voltage till you get the original Average CPM to and monitor it to see if it behaves same as before.
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Reply #6

ChrisP

Austria
6 Posts

Posted - 07/10/2020 :  12:52:58  Show Profile  Reply with Quote
I tested voltage reduction down to 20% for tube 1 but it does not seem to have a significant impact. At the moment I have 32CPM with avg 27CPM and max. 90CPM for the last 4 days. I think I should return the unit for warranty.
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Reply #7

EmfDev

1243 Posts

Posted - 07/10/2020 :  14:35:12  Show Profile  Reply with Quote
Looks like the tube needs to be replaced. Please email customer support@gqelectronicsllc.com for warranty.
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Reply #8

Rog15

USA
3 Posts

Posted - 07/28/2020 :  09:11:37  Show Profile  Reply with Quote
Just a note, I left a detailed response on the rad spike topic. Jul 9 & 10 had major spikes early morning to afternoon here in NE WI. Was way over 10 mR/hr on old meter. Strongest like 3-4am, then tapering to waves then bursts. Very freaky. Iran's supposed nuc facilities were exploding that week. Related? Just got GMC-320+, will get it on the map asap. Cheers & stay safe.

Roger Schutt KD9EPX
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Reply #9

ullix

Germany
491 Posts

Posted - 07/30/2020 :  01:58:36  Show Profile  Reply with Quote
As will all such problems: verify that the Anode voltage is in the proper range!
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