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stilldavid
USA
1 Posts |
 Posted - 04/09/2013 : 06:37:10
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I recently took a GMC-300 unit to an area of very high radioactivity as a backup unit, as well as for the logging capabilities.
I'm wondering about the unit's maximums. I've read in other posts that the maximum CPM is 65,535 (2^16), and I was able to reach this maximum very easily where I was. Here is a reading of 64,888 CPM which reads as ~325 uSv/h:
This is a very high reading, to be sure, and I didn't stick around this area for long. A few feet away the readings dropped back to less than 3uSv/h, which I consider to be safe for an extended period of time. My issue is that when encountering very high readings, the difference between 50, 100, 500 and 1,000 uSv/h is not necessarily life threatening, but it would certainly change my behavior in the situation. It might be worth having a "maximum reached" warning of some sort. In the case above, I was able to read 1.3mSv/h (that's 1,300 uSv/h) with a GammaScout - which is admittedly more expensive - and believe me, I left very soon after.
In addition, in very high radiation environments the GMC-300 seemed to "reset" every minute or so. I'm guessing it does a one minute average to store readings (I was in 1m save mode), but the average would be much more useful if it was a rolling average. If I look down and see that the uSv/h reading is only 1 or so, I will not think twice, but after a few seconds it might jump to 15 or 30 uSv/h, much to my dismay. I think a continual rolling average would solve this problem, and not be very difficult to implement.
At any rate, this piece of kit is great for the price and I'm otherwise happy with it aside from a few other quirks. I would like to see Mac support as well, but I'm working on a python script to read the saved data into a CSV.
If the issues in high radiation environments can be fixed, I think it's got a lot more of a shot of competing with the more expensive models. |
Edited by - stilldavid on 04/09/2013 06:37:32
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| Reply #1
ZLM
1261 Posts |
Posted - 04/12/2013 : 13:50:07
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Thank you for your useful information.
Yes. The maximum reading on display is 65535 CPM. It will rollover if the reading more than that.
The Geiger tube is installed at the lower part of the unit. So, if your upsidedwn the unit, you may get even higher CPM.
I have not experenced in such high radiation environment. I think I need to test my unit to see if it resets automatically. Once the problem can repeat, then it should be a fix. In this cae, the unit CPU may be too busy on calculation and it forgot to feed the software watch dog. then the software watch dog expiered and init a reset. If this is the case, then there is a easy fix.
The warning message should be easy to add.
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| Reply #2
Distelzombie
Germany
202 Posts |
Posted - 11/11/2015 : 02:48:11
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Hi There.
I have a similar question. With my pitchblend I'm reading over 65535 CPM. What exactly do you mean with "rollover"?
Can I simply add the CPM measured after the gmc reached 65k and "rolled over" to the 65k and take this sum as the actual measurement?
If so, then I measured about 78k CPM. How can I translate that to ySv/h? I don't know the exact max ySv/h.
It would be best to change the reading to CPS after CPM maxed out. I suppose the ySv/h's maximum is also 65k, making this the best solution by simply eliminating the current limitations of measuring of the device.
Would that be possible? |
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #3
ZLM
1261 Posts |
Posted - 11/21/2015 : 09:13:06
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The CPM can be added to 65535 after rollover. But all other dose unit can not be added to roll over.
Example, if the reading is 2000CPM after rollover, then the real CPM is 67535 CPM.
It is a good idea to change to CPS after CPM maxed out. But current firmware has no way to change it. |
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| Reply #4
Distelzombie
Germany
202 Posts |
Posted - 11/22/2015 : 07:00:07
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Thank you for clarification. :)
Would be awesome to see this added to the next firmware. But if that's impossible... :(
But now that I know the conversion rate is standardly 0.005 ySv/h per click, we can calculate the ySv/h:
78000 CPM would be 390 ySv/h (78000*0.005)
Using the other conversion rate recommended by people on the Internet who calibrated their device: 0.0065=> 507 ySv/h
I'm still not sure which to choose. I need a check source. :/ |
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
Edited by - Distelzombie on 11/22/2015 07:15:48 |
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GMC-300 Max Readings
