| T O P I C R E V I E W |
| ullix |
Posted - 03/07/2021 : 09:20:56
I got a brand new GMC-300E+ and something raised my suspicion. So I took the back off and lay the counter on the edge of my desk, face-down, tube now facing upwards, and let GeigerLog do the recording. This is the result:
Even without any arrows or marks you can easily see the times of sunrise, sunset, and the moments that clouds covered the sun. And the counts easily exceeded the counts I could have created with my whole collection of radioactive samples!
My office has daylight, but certainly no glare. Light is dimmed with curtains to easily allow working at a computer monitor. This is daylight behind windows, so very little UV. I also tried "Black light" of 395nm from LED, and the counts went to CPM well beyond 10000!
Let's look at the tube:
First surprise: not an M4011, but a J305! Second surprise: not a blackened tube, but again a clear glass one.
Compared to a M4011 the J305 is approx 5 mm shorter. You see in the pics that the tube is forced into the holding clamps with cable ties.
A smaller tube means less sensitivity. Wondering what the "calibration factors" will look like? Surprise, surprise, they are exactly the same at 0.0065 uSv/h/CPM, or as I prefer the inverse as Sensitivity, a sensitivity of 154 CPM/uSv/h.
And why should it be changed? As I had said without ever being contradicted by GQ, there has never been a calibration of any tube, be it M4011 or now J305, so why would one bother with changing anything which is made-up anyway?
But while the basics aren't right, we get such advanced features as FET, and auto-voltage adjustment! I wonder what auto-voltage my light tube would have generated?
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| 10 L A T E S T R E P L I E S (Newest First) |
| Damien68 |
Posted - 03/13/2021 : 04:27:48
quote:
Originally posted by ullix
I've got a blue-laser pointer, 405nm, 5mW, which makes an oblong "spot" of some 3x5mm. Not perfect but much more suited than an LED flash light to sample the Geiger tube for light sensitive areas.
90k CPM is very high,
maybe the glass insulators are not made with the same glass quality as the tube?
or can be sensitif components for welding but it seam to be autogenous one, but not sure it's a little gray |
| ullix |
Posted - 03/13/2021 : 03:30:55
I've got a blue-laser pointer, 405nm, 5mW, which makes an oblong "spot" of some 3x5mm. Not perfect but much more suited than an LED flash light to sample the Geiger tube for light sensitive areas.
So I set the counter speaker to ON, and illuminated the tube spot-by-spot. As a result: no areas are light sensitive, EXCEPT two spots circled in the picture, one on the Anode side, one on the Cathode side. The circles are about the size of the laser spot.
Sensitive is only the immediate area where the anode rod enters into what seems to be a little glass tube, presumably simply the mechanical holder for the anode rod.
The two sides are differently sensitive: the cathode end generates some 100 CPS, but the anode end easily generates CPS=1500, i.e. CPM=90000!
But even with a 20x magnifying lens can I see any difference between the two ends, nor anything else noteworthy. No metallic smear, no rainbow colors, nothing. Does anyone see more?
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| ullix |
Posted - 03/12/2021 : 02:28:58
quote:
... on the end furthest away from the USB port
That means it is the cathode end of the tube. We had seen this already in this topic "Light-Sensitivity of a GMC Counter - Yet again!"
http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=9287
(hope this link is working?) Reply#22.
This confirms again that the cathode is the problematic area. I just don't understand why this is so. Responsible for this photoelectric effect is likely a metal. (More explanations in Reply#31 of above link.) But why the difference between cathode, middle, and anode?
If you really want to create light counts use a flash light with LEDs at 395nm. I use this one, which also offers 365nm: https://www.amazon.de/gp/product/B081TDXP9R
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| cynoclast |
Posted - 03/12/2021 : 01:21:20
quote:
Originally posted by EmfDev
@ullix, can you email support for your order number and address? and also to let them know you tube is defective and they will send you a good tube.
We do QA check for this but unfortunately some tubes still pass. Just checked few more tubes by putting them DIRECTLY under sunlight and non of them had this issue.
We have made changes with the design/tube to prevent this issue from happening.
Hello! I was referred here from a thread I may have accidentally necro'd: http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=9287&whichpage=2
I bought my detector via amazon so I don't have an order number from GQ...
FWIW I was able to crank my detector up to over 5K CMP with this headlamp: https://www.amazon.com/Black-Diamond-Spot-Headlamp-Size/dp/B06W54SBSL/ (main/right LED)
Just pointing it up into the bottom of the detector/tube on the end furthest away from the USB port. Hopefully this will help with testing/QA even if it doesn't help me.
What is support's email address? And is my order on May 8, 2019 covered at all? (It has always worked like this I just never got around to dealing with it seeing as how I had no symptoms of acute radiation sickness.) |
| EmfDev |
Posted - 03/09/2021 : 13:39:40
@ullix, can you email support for your order number and address? and also to let them know you tube is defective and they will send you a good tube.
We do QA check for this but unfortunately some tubes still pass. Just checked few more tubes by putting them DIRECTLY under sunlight and non of them had this issue.
We have made changes with the design/tube to prevent this issue from happening. |
| ullix |
Posted - 03/09/2021 : 01:26:36
quote:
Seems like tube is defective.
ok, so may I get a replacement tube? You do have my address.
As this is such an obvious effect : is there ever any QA to check for such defect tubes?
quote:
It is not designed under direct sunlight/exposed.
... and it was not exposed to direct sunlight. Or are you personally exposed to direct sunlight when you sit at your desk? Neither am I, not the counter which lay on my desk.
quote:
Need the back case cover.
This is a pretty lame excuse. The case cover has open slits which lets light pass through. In addition, the material of the case is translucent, so light also gets through on this path, and then there are white LEDs inside the counter to illuminate the LCD, also contributing.
Putting the case on would mitigate the light problem, but only a completely light-tight case could do the job right. Such a case does not exist!
Judged by my own haul-out of light-sensitive tubes obtained from GQ, 50% of the tubes will have this defect! Give or take a few percent, but the number will be significant!
So now all those people posting their counts on the "Radiation World Map" effectively are posting sunshine levels at their location pretending it has anything to do with radioactivity.
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| EmfDev |
Posted - 03/08/2021 : 12:32:53
Seems like tube is defective. It is not designed under direct sunlight/exposed. Need the back case cover. |
| Damien68 |
Posted - 03/08/2021 : 02:38:23
given the thickness of the blue line I would say that the weather must be cloudy in your area in Germany. this gives variations.
given the steep decay after 3pm, I would say you must lose direct sunlight at this time, so your office must be facing southeast
what is the radioactivity in your office? uh ... what?
 |
| Damien68 |
Posted - 03/07/2021 : 11:34:46
quote:
Originally posted by ullix
I got a brand new GMC-300E+ and something raised my suspicion. So I took the back off and lay the counter on the edge of my desk, face-down, tube now facing upwards, and let GeigerLog do the recording. This is the result:
Even without any arrows or marks you can easily see the times of sunrise, sunset, and the moments that clouds covered the sun. And the counts easily exceeded the counts I could have created with my whole collection of radioactive samples!
My office has daylight, but certainly no glare. Light is dimmed with curtains to easily allow working at a computer monitor. This is daylight behind windows, so very little UV. I also tried "Black light" of 395nm from LED, and the counts went to CPM well beyond 10000!
so ridiculous, That's too bad whatever the price of the counter. |
| Damien68 |
Posted - 03/07/2021 : 11:30:56
unbelievable! |
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