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newgcuser
1 Posts |
 Posted - 07/21/2022 : 21:51:21
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Hey folks,
New user here. Bought a GQ-GMC500+ Off of Amazon two weeks ago to check indoor Radon levels. I just turned on the unit, (50% battery out of the box), followed the simple instructions turning on and setting date and time, got very high readings indoors at home and moved the unit to the patio outdoors and still registered seemingly high levels. Is this due to unit defect? bad calibration? What should I do? I currently don’t have a second different brand meter at hand to compare readings.
I uploaded a picture. taken on the patio when I placed this unit on the patio floor. It’s 2100 or so CPM (I did this because when I first turned it on indoors it was like high 3000s or so just on the table in the first floor and 2500 or so on the second floor when I hold it). I mean I never had my house tested for radon or anything and I don’t have any sources of any kind of radiation that I know of at home. And I live in a normal residential community in northern virginia. (I ordered a radex one and an airthings radon monitor just now and both should arrive soon so I can have a comparison) but in the immediate time what should I do?
Please advice?
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| Reply #1
ullix
Germany
1112 Posts |
Posted - 07/21/2022 : 23:46:26
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That count rate does not look right.
But by now you see how awful it is to upload huge pictures! The rule should be to limit picture size to no more than about 800 pixels wide.
You can fix this be editing your own post: delete the existing picture, shrink it to something more manageable, and re-post it.
The cause of the high rate could be multi-fold. Let's try some prime candidates:
1) Light sensitivity: in my experience, some 50% of the glass tubes give counts when exposed to light. Read the counter in complete darkness. Still high?
2) Anode voltage: newer counters have a menu entry, which supposedly tells you the anode voltage. It should be near 400V. Is that the case? But this reading may or may not be correct.
3) Anode voltage: open the counter, use a DVM and measure voltage across the tube (endcap to endcap). Problem: with the measurement the voltage collapses, and even if you had the proper 400V, you would measure only something between 100 ... 150V. You need a 1 GigaOhm resistor in series with the DVM to do better. Is much discussed elsewhere int the forum.
4) tube selection: newer versions allow to switch off either of the tubes from recording. Select tube#1, then tube#2. Do you get high counts with each tube? (If so, I'd say there is an electronic defect, and the counter needs to be repaired of replaced).
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| Reply #2
EmfDev
2148 Posts |
Posted - 07/25/2022 : 09:16:32
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Hi newgcuser. Please try a factory reset. And try to go somewhere else and see if the radiation is real or not.
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New GQ-GMC500+ First Indoor Reading 2500+??!
