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HP41
USA
2 Posts |
 Posted - 10/12/2025 : 17:58:22
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I recently received a GMC-800 from Amazon. When I first opened the package the unit appeared to be new except for a couple of scratches on the plastic film protecting the screen. Next, when I turned the unit on, I noticed the battery level was at 98%. That seemed to be too high for a new unit that had to be shipped. I next installed the “GQ Geiger Counter Data Viewer” software and downloaded all the logged data that was stored on the unit.
On inspection of the data, I found there were a few minutes of my data dated 10-12-2025 at the end of the file, and 4 minutes of data logged on 7-22-2025 at the beginning of he file. I took the latter to be the result of possible testing during manufacture. In between however, there was almost an hour of data produced on 9-8-2025. Most of the data on 9-8-2025 as presented by the software, indicated a CPM value of around 20, except for one minute when it spiked at 54.
This combined information would seem to point that this is a returned unit that was shipped as new. Although this is disconcerting, the real problem is if it was returned, why was it returned? This is all brand new to me so I have no experience to judge if it is working at 100% or not, or the wisdom to determine if I should accept it as is.
Is there any way of testing to see if it meets specs? I did not see a reference in the manual for any user on-board diagnostic tools, only a menu for a qualified calibration facility.
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ullix
Germany
1222 Posts |
Posted - 10/13/2025 : 01:16:14
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If you think to see clear signs of previous use, I would return it.
However, chances are it is still ok.
Since you don't seem to have any good radioactive sources to test, I suggest to go the Potassium way. For explanation see my article "Potty Training" https://sourceforge.net/projects/geigerlog/files/Articles/
For a first try: Put the counter on a table somewhere in your living room, and get average of CPM for about an hour. Then hold counter onto a tile in the batroom, and measure again for an hour. You should see a higher value (tiles are likely to contain K-40).
For even better validation install GeigerLog, record for some time, and make Poisson test (see GeigerLog manual). If that comes out well, the counter is likely ok.
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| Reply #2
HP41
USA
2 Posts |
Posted - 10/13/2025 : 11:31:00
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| @ullix: I thank you for taking the time to reply and for your suggestions. They made me think about what I might have for testing purposes, and I then remembered that I had a WWII period family heirloom around the might have radioactive characteristics - and it did so in spades, at least in very close proximity to the GMC-800's sensor. Obviously I cannot confirm the accuracy of the readings, but I am never going to be documenting research, so I expect it is accurate enough. As a result I plan to keep the GMC-800, even though I am disappointed that I was likely shipped a returned unit as being new. Thanks again for your help, and case closed. |
Edited by - HP41 on 10/13/2025 11:33:05 |
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Returned GMC-800 Sent As New ???
