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Common Table of Geiger-Müller tubes
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LND
| Name | Type | A/B/G | Voltage | R10a | Conversion Factor | Compatible | Notes |
|---|---|---|---|---|---|---|---|
| LND 712 | Tube | A/B/G | 500V | ? | 0.00233? | - | - |
Frieseke & Hoepfner
| Name | Type | A/B/G | Voltage | R10a | Conversion Factor | Compatible | Notes |
|---|---|---|---|---|---|---|---|
| FHZ 76 | Tube | -/B/G | 500V | ? | 0.00233? | - | 1r/h |
| FHZ 74 | Tube | -/B/G | 500V | ? | 0.00233? | - | 50r/h |
| SBM-20 | 0.00277 |
| SI-180G | 0.00321 |
Discussion
Hi,
what do I get with the above conversion factor * count → mSv?
Do I subtract the dead time per count from the measurement time?
Can you show the calc of counts to the usual representation nSv / h?
I have the FHZ 76V tube
Grüße aus Landshut
ralphi
Yeah, I don't know why, but there is very little actual/credible information about it out there on the net. We've tried to collect and verify what we could and came up with convert-cpm-to-usv-h. In tests, comparing with other counters at LDR, the equivalency results were pretty much the same.
uSv/h seems to be the base for most formulas in use out there, so we've simply adopted it; other magnitudes derive from there.
When in doubt - use the source, luke:
https://github.com/apollo-ng/PiGI/blob/master/software/pyGI/geigercounter.py#L106
(edr = equivalent dose rate)
Any updates, corrections and more insight are always welcome.
Hi Chrono, I find a verified measuring station from “Bundesamt für Strahlenschutz” right in my area. http://odlinfo.bfs.de/DE/aktuelles/messstelle/092741261.html The factor is one shift diffrent –> to µSv/h x 0.000233 or nSv/h - x 0.233 ralphi
Ah, totally missed that, which tube was that?
Hej,
is there a known value for R10a for the sbm20 tube? I don't have access to a gigaohm resistor right now, and thought that someone maybe knows the value. Also, do I always need an additional resistor on the anode of the tube? I am somewhat confused…
Thanks for this great resource,
Timo
Hey Timo,
so far, no R10a value for a certain tube has bubbled up to my knowledge. It was just implemented to accommodate for future, larger productions, where a specific known working board/tube configuration could be replicated easily. If I ever find the time, I can try to measure the values of the trimmers for my tubes as an indication.
If you're in trouble setting the HV, you can also work slowly and work by ear. So far all of my modules were emitting a certain switching “feep” when they were in working voltage range and it stops completely when you're “overdoing” it and voltage breaks down. Having a test source nearby would be the other option to dial it in.
As for anode resistors: I haven't tried without it yet.
Hej Chrono,
Thanks for your answer.
I was thinking about eyeballing it, but I was super worried about “blowing up” and damaging one of the tubes. How big is the danger of doing that?
I´m planning to use either an SBM20 or the SI1G, because I have a specimen of each.
Concerning R3: It should be possible to add another one of those 4.7mΩ smd resis in series to R3 to get closer to the 10mΩ anode resistor, right?
Thanks again for you help,
Timo
I wouldn't worry too much about it, so far they've been pretty robust and even cranking up to the trimmer's limit had no effect on the tubes. At some point the HV just collapses. Also, if you don't want to get a gig-ohm resi, you can always hack around by taking a couple of the highest value resistors you can find at hand, and put them in series. It'll not be precise, but I think I left a calculation example in the hardware section to get a ballpark figure.
Have a look at:
You can see that, additionally to R3 on the board, there is a TH resistor connecting the anode to the pad. You want that resistor to be as close to the anode as possible. I've no personal experience with your tube types, so your mileage may vary.
Is that a personal/hobby project or are you doing something university related with it?
Ok, that makes me a little more relaxed, thanks. Is it okay if the gigaohm-resistor is only a 0,25w one? I would be able to get one of those relatively cheap.
This is for a uni-project, I want to use the PiGi as an entropy source for an electronics project. Also somewhat of a hobby-ish project, for I am just interested ;)
Thanks for your help, Timo
Wondering if any experience with https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F273803466571
Or
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F352595909392
With your board. I got one pre-assembled yesterday. I have two SBM-20 based detectors, so looking for something that can detect alpha as well.
Never tried any of them, but their specs read pretty compatible to PiGIs HV generator so they should work. It'll probably be a little harder to get reliable conversion factors or need some other tube/test source to tune it for equivalency metrics, CPS/CPM should be fine.
there is an interesting discussion of the conversion rate for the si-22g: https://github.com/ecocurious2/MultiGeiger/issues/20 they problematize contradicting conversion rates for this tube circulating on the www. after their own calibration measurements they come up with their own value. it summs up to ~0,001357 if my math is right.
Thanks for the addition