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Benezi
15 Posts |
 Posted - 05/11/2014 : 12:21:28
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Hello Guys!
I bought the GMC320+ last week and now I'm a bit confused.
In the Internet it says that the M4011 counts about 30-40 CPM background radiation. But my GMC says only about 10-15.
I calibrated the GMC and it was only half sensitive as it should be refered to the settings when it came last week. My conversion factor for CS-137 now is uS/h = CPM * 0,0098.
I read that there is a pot to increase the voltage of the tube.
Do you think that this would help to increase the sensitivity of the tube?
Or is all right with my GMC?
Thank you for your help guys and sorry for my bad english,
Regards from Germany,
Benedikt |
Edited by - Benezi on 05/11/2014 12:51:15
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| Reply #1
ZLM
1261 Posts |
Posted - 05/11/2014 : 22:01:53
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Background 10-15 CPM is normal.
The background CPM may be vary depending on the location. My GMC-320 background is 10-15 CPM too.
Higher CPM background tube does not means sensitive.
increase the tube voltage will increase the sensitivity. But it reduce the tube life. Also, you need to recalibrate the unit.
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| Reply #2
Benezi
15 Posts |
Posted - 05/12/2014 : 03:17:37
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How could I increase the tube voltage?
Regards, Benedikt |
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| Reply #3
ZLM
1261 Posts |
Posted - 05/12/2014 : 09:15:47
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| For the GMC-320+, there is a blue potentiometer. Turn it clockwise increases the tube voltage. |
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| Reply #4
Benezi
15 Posts |
Posted - 05/12/2014 : 10:45:30
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Whats the maximum?
In the Internet it says that I need 380-450V but if i use my Voltmeter it just says between 0 and 200V?
Or can I just use maximum Voltage?
Regards and thank you very much,
Benedikt |
Edited by - Benezi on 05/12/2014 10:56:30 |
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| Reply #5
ZLM
1261 Posts |
Posted - 05/12/2014 : 22:17:12
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| To get accurate tube voltage reading, you need to serial a 100M resistor and then do a calculation. |
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| Reply #6
Benezi
15 Posts |
Posted - 05/12/2014 : 23:06:42
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Where can i find more Informationen about that?
Thanks,
Benedikt |
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| Reply #7
ZLM
1261 Posts |
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| Reply #8
Alchemy2
Canada
89 Posts |
Posted - 05/29/2014 : 12:24:24
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| I checked the GMC-320 unit I have against a known source with a dosimeter using the same 4011 tube. both read same for me, and my background varies a bit between 10-20 mostly closer to 16-18CPM. I'm fine with mine! |
The more I learn, the more I realize I do not know! |
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Topic |
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GMC320+ too low Background
