fix Si22G GM tube count to uSv/h conversion factor

[ThomasWaldmann]

See XXX FIXME in the source code.

[ThomasWaldmann]

Related:

https://www.pocketmagic.net/tube-si-22g-c%D0%B8-22%D0%B3-sensitive-geiger-muller/

https://www.uradmonitor.com/topic/hardware-conversion-factor/ https://github.com/radhoo/uradmonitor_kit1/blob/master/code/geiger/detectors.cpp

http://arduino-geiger-pcb.blogspot.com/2017/03/conversion-rates-for-soviet-made-geiger.html

http://home.agh.edu.pl/~bartus/index.php?action=efekty&subaction=arduino&item=33

[ThomasWaldmann]

From current source code (cps -> uSv/h):

const float GMZ_factor_uSvph_SBM20 = 1/2.47;      //   for SBM20 (== 0.404858)
const float GMZ_factor_uSvph_SBM19 = 1/9.81888;   //   for SBM19 (== 0.101845)
...
Dose_Rate = Count_Rate * GMZ_factor_uSvph;

Note: Count_Rate == cps.

[ThomasWaldmann]

based on uradmonitor (cpm -> uSv/h and cps -> uSv/h):

SBM20: 0.006315 // 60 == 0.3789 SBM19: 0.001500 // 60 == 0.0900 Si22G: 0.001714 // * 60 == 0.10284

[ThomasWaldmann]

based on arduino-geiger-pcb (cpm -> uSv/h and cps -> uSv/h):

SBM20: 1 / 220 == 0.00454545 // 60 == 0.272727 SBM19: 1 / 928 == 0.00107759 // 60 == 0.0646554 Si22G: 1 / 792 == 0.00126263 // * 60 == 0.0757578

[ThomasWaldmann]

So, 3 geiger counters and 3 quite different sets of conversion factors. Which ones are correct?

As a general note: https://en.wikipedia.org/wiki/Sievert

Obviously, calculating Sv from CPM (CPS) is not trivial at all and depends on quite some factors a GM tube does not measure at all (it only measures events, it does not measure radiation energy, it does not detect kind of radiation [assuming it can detect multiple kinds]).

[rexfue]

I think it's always just an estimate. The factor depends on too many influences. Juergen will tell us the factor for Si22G in the next days.

[ThomasWaldmann]

There should be also a comment above these lines, where these values come from / how they are calculated.

[ThomasWaldmann]

@WwwBoehriDe (guess this is you, Juergen?), can you have a look?

[WwwBoehriDe]

Hi, yes, I am working on that. I can find two values - quite confusing. Bu I think I will come back to this this week.

[ThomasWaldmann]

Note: because this is yet not fixed in master and we had the Si22G tube, we've seen 5x too high nSv/h values on the correctly counting geiger last Sunday at shackspace.

Lesson: use factor 0.0 next time to be obviously wrong/unsupported rather than displaying confusing/disturbing values.

[ThomasWaldmann]

Note: the code right now has factor 0.0 for the Si22G (see previous comment).

[ThomasWaldmann]

Yet another idea! :-)

If we use a -1.0 conversion factor, the output code could check for negative values and emit ??? or unknown instead of the value.

[ThomasWaldmann]

What we can expect, check this against MultiGeiger displayed values.

https://odlinfo.bfs.de/DE/aktuelles/messstellenliste.html

City and Gamma-Radiation uSv/h 22.11.2019 22:45 Asperg: 0.113 Böblingen: 0.114 Esslingen: 0.103 Löchgau: 0.112 Sindelfingen: 0.110 Stuttgart: 0.111 Tübingen: 0.097

[WwwBoehriDe]

I am working on that. There are two differnet values in the internet. The next day I want to make a comparing measurement next to the Sindelfingen ODL-Station (I hope I can find it :-( ).

[ThomasWaldmann]

@WwwBoehriDe did you already try finding it? the map on the bfs site seems to be rather precise.

[WwwBoehriDe]

Hi, yes, I did measure and compare it directly at at the governments ODL-Station Sindelfingen. So I was able to calculate the correct value for the Si22g. There was no good value in a datasheet :-(. The Constant for the Si22g geiger tube I measured is: 44205 Counts per uSv...

So the Resulting factor for the sofware is: 0.08143875127248 (uSv/h) per (Counts per Second)

[ThomasWaldmann]

Ah, great. And it's even in between the other 2 known values. :-)

I'll update the code...

[ThomasWaldmann]

See #94.