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ullix
Germany
1177 Posts |
 Posted - 12/01/2024 : 06:15:04
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This had been a hot topic some years(!) ago, but I taught GeigerLog some new tricks, so I tried it out.
GeigerLog can now communicate with a Bluetooth coupled DMM (Digital Multi Meter) so I could very conveniently measure the Anode Voltage (via 1 GOhm) of a Geiger counter, and read it into GeigerLog.
The counter was a GMC-300E+. The DMM an OWON OW18E (very nice AND LowCost!). I had the counter's backplate removed, and put increasing amount of "stuff" onto the naked tube (M4011) and recorded in GL (Note the LOG scale for CPM!):
CPM of some 6k is the best I could do. I know some of you can do more; you are encouraged to test it out!
The collapsing Anode voltage (in green) is already clearly visible.
Every Geiger tube has a certain minimum voltage, below which no counts whatsoever will be created. For the M4011 tube this minimum is 350V. For some deeper insight I plotted Volt vs CPM for the 4 value pairs. Assuming linearity - which seems to be given - the graph shows that this cutoff voltage of 350V is reached at about CPM=13500 or CPS=225:
Is this in agreement with what GQ is saying about their counter's range? In the manual of the GMC-300E+ I see:
With their "calibration factor" of 154 CPM / (µSv/h) this becomes CPM=50510 / CPS=842.
Really? I think this is a faaar cry away from reality!
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Edited by - ullix on 12/01/2024 06:29:31
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| Reply #1
ihab17
Italy
219 Posts |
Posted - 12/02/2024 : 23:19:49
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| You're da Man Ullix! Ullix for president! |
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| Reply #2
EmfDev
2260 Posts |
Posted - 12/03/2024 : 18:21:24
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hmm actually, the calibrated value for the GMC-SE (similar firmware and hardware) can go up to 200mR/h = 2000 uSv/h.
the multimeter is probably drawing current from the power supply.
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ullix
Germany
1177 Posts |
Posted - 12/04/2024 : 01:46:11
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Yeah, with a 1 GigaOhm resistor in between?
And the DMM, which is present for all count rates, is pulling increasing current with increasing count rate? So, effectively, the DMM would be the better Geiger counter for any count rates, uncluding very much higher ones?
The problem is not the collapsing voltage, the problem is your exaggerated claim about max count rate!
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Edited by - ullix on 12/04/2024 07:06:17 |
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| Reply #4
ullix
Germany
1177 Posts |
Posted - 12/04/2024 : 07:13:16
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quote:
hmm actually, the calibrated value for the GMC-SE (similar firmware and hardware) can go up to 200mR/h = 2000 uSv/h.
It does not matter what your claim is, when this device is based on the same hard and software, and you claim an even higher max count rate, then your claim is even much farther away from the true value!
Prove it isn't. |
Edited by - ullix on 12/04/2024 07:13:34 |
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ZLM
1269 Posts |
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| Reply #6
ullix
Germany
1177 Posts |
Posted - 12/09/2024 : 08:07:17
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Surprising video, indeed!
As I had access to a GMC-300s, I repeated my test, with the result shown in pic.
The GMC-300s starts at an anode voltage of 350 Volt, which I think is already borderline for a claimed M4011 tube. But as the tube is wrapped in black plastic, I can't say what tube it really is.
On my GMC-300s I see no option to change the anode voltage, neither is there any hardware nor any software option.
Given the voltage response as shown in the pic, I don't expect that this unit could make it to CPM=60000! It would be down to about 200 Volt.
Have you modified your hardware in any way? Which way? What voltage does the device show at background count rates, and what at CPM=60k ?
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| Reply #7
ZLM
1269 Posts |
Posted - 12/12/2024 : 20:31:46
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| The GMC-300S in video is standard design without any modification. As I know, the tube installed is J321 and the minimum voltage can be as low as 240V. But I did not verify the voltage dropping is linear or not. This device background rate is about 15-25CPM. |
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Collapsing Anode Volts with increasing Count Rate
