| T O P I C R E V I E W |
| ullix |
Posted - 04/04/2017 : 04:06:51
From my Geiger GMC-300E plus v4.20 I get the values for the calibration points as:
Calibration Point 1: 60 CPM = 0.39 uSv/h (Factor 1: 0.0065 uSv/h / CPM)
Calibration Point 2: 240 CPM = 1.56 uSv/h (Factor 2: 0.0065 uSv/h / CPM)
Calibration Point 3: 1000 CPM = 6.50 uSv/h (Factor 3: 0.0065 uSv/h / CPM)
I read this as 3 calibration points, which however are set to make a strictly linear relationship between CPM and uSv/h.
Since you are providing 3 separate points, you seem to be expecting a non-linear behavior. So what is the argument for them not being necessary as this default setting suggests?
And what would make me want to calibrate the Geiger differently?
And how would I use different calibration points? Would I multiply everything up to 60 CPM with Factor 1, and multiply everything above 60 CPM with Factor 2 and add to together etc? Or how? |
| 5 L A T E S T R E P L I E S (Newest First) |
| Distelzombie |
Posted - 04/10/2017 : 09:23:39
... I was saying that the factory default value was once 0.005... I simply didn't want to check what it is now because I have other values ... Dude, dont be so anti... |
| ullix |
Posted - 04/10/2017 : 08:11:12
@Distelzombie:
Please, don't make yourself look foolish; neither did I use your value nor am I wrong.
The data I presented were copy & pasted from my program, but you can also find them by searching through the menus of the device itself. These are the factory defaults of my device; device type and firmware are clearly specified in my question, and from here you go by simple math.
Take e.g calibration point 1: when at 60CPM the Sievert value is 0.39 µSv/h, you divide 0.39 by 60 and get 0.0065 µSv/h / CPM. Try it with the other 2 and you get the same factor. It is that trivial.
Hence, in total we have 3 calibration points, each defining the same slope. In effect, we have a single point calibration of
CPM * 0.0065 = µSv/h
I am not saying that this is wrong; there may be good enough reasons for it. But when I see provisions for a three point calibration, which are not being used, and then see all calibration points lie in the bottom 1% part of the range to be calibrated, I am beginning to wonder. For a range of 0...65000 I would expect calibration points spaced e.g. at 200, 2000 and 20000 and not 60, 200 and 1000. But it all depends on the type of curve CPM vs µSv/h. Which also is unknown, but can be assumed to be non-linear only at the upper end.
An explanation from GQ might clarify this.
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| Distelzombie |
Posted - 04/09/2017 : 13:08:51
Also we dont know what exactly the changes to the firmware regarding that bug were. Is there still a drop from one point to another? You (ZLM) didnt even respond to this thread i posted here telling us its a bug and it gets fixed. I got this information from other threads that came up later
It seems like the factory default calibration has been changed from 0.005 to 0.0065 (or Ullix is wrong and used my value I got from a webpage that calibrated a device using the same tube. I havent checked yet)
For now it seems like the app i used to measure stuff is the best choice if you want correct measurements above 65535 CPM. (I recently got the cpm screen to wrap around two times and more...) |
| ullix |
Posted - 04/08/2017 : 02:26:57
@GQ and @ZLM:
I wish you would be a bit more forthcoming with information on your system! There are quite a few questions on particularly calibration, yet answers are coming dripping in or not at all. Relevant information is often only assembled by users and discovered only after some elaborate digging.
Like this document Geiger_Tube_theory.pdf on Phil Gillaspy's site https://sourceforge.net/projects/gqgmc/files/gqgmc/. Theory suggests that Geiger tubes have a dead time of 50 - 200 µsec. This amounts to a maximum worst case CPS near 5000 or CPM 300,000. At those rates there might be saturation depending on tube, calling for a calibration factor taking this into account.
But the maximum count rate of CPM=65535 (resulting from the 2 byte limit on your counters) is sufficiently below that presumed limit to perhaps justify a linear calibration only. Or not?
However, as departure from linearity is in the highest rates only, then if 65535 is the limit, why is the highest calibration point at 1000, i.e. all 3 calibration points are in the bottom ~1% of the possible range???
And since you factory default calibration is 0.0065 µSv/h / CPM where was this take from or how was this determined?
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| Distelzombie |
Posted - 04/07/2017 : 09:02:03
Maybe to mimic energy compensation?
On the other hand, it could be used to conquer the lesser sensitivity when the gas gets ionized. (what other tubes use flushing gas for.)
There once was a firmware bug and I asked ZLM a out this. This thread includes his answer to your question: ://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4204
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