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uRADMonitor â€“ Online remote radiation monitoring station

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radhoo

Fri Oct 12 2012, 07:55PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Proud Mary wrote ...

CPM is always true, but there are many and complex variables converting CPM into a dose rate, as you know, and if it was my project, I would not bother.

Yes, this is probably the best option, given my limited tools at this moment.

Proud Mary

Sat Oct 13 2012, 10:00AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I have just realised that a GM tube will be perfectly good for observing most background radiation because the three main terrestrial components of background gammas are K-40 1462 keV, Bi-214 1760 keV from the U decay series, and Tl-206 from the Th decay series. Smaller contributions to total background come from Pb-212 239 keV, Bi-209 609 keV, Tl-208 908 keV and Bi-214 1120 keV

As you know, the most serious non-linearity of energy response in uncompensated GM tubes occurs below 150 keV - and most of that below 100 keV - so none of the background emissions I've listed above will be seriously affected, nor will the majority of cosmic rays.

The most seriously affected - and, in many ways, the most interesting - part of the background gamma spectrum that will fall within the GM tube's most non-linear energy response region is skyshine - the radiation scattered by the air above both natural and man-made sources like particle accelerators, reactors, and high-level waste dumps. Most skyshine falls below 500 keV, and most of that below 100 keV. However, unless you live near a uranium ore body, or a nuclear facility, or we have another Chernobyl event, skyshine will not be a significant part of data gathered by a GM tube!

So, I would say that CPM to Î¼Sv/hr conversions using manufacturers data based on either Cs-137 or Co-60 will not be too inaccurate to be of use across the natural background gamma spectrum. An integration period of four hours should be used for reliable gamma background assessment.

radhoo

Sat Oct 13 2012, 04:43PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Those are some very pertinent and useful observations, Proud Mary, thank you for highlighting that. After all , the device will work as a natural background observer, nothing else.

Here is the diagram for the current version 3.3.103:

Source code is also available here:

I need to build a box, and put everything together. Here's how it looks like now:

This is what you've been connecting to via the webbrowser.

Not only the box , but some changes in the software to make it export data to my blog, instead of working as a webserver. Also I need to make it support DHCP, so it would work in any switched LAN with simple plug and play. Then at the other end - on my blog's server, the exported data will be stored in a SQL data base and presented as a nice chart, with various selectable parameters. Lucky that I'm trained as a software developer... still this will take a few more days.

Proud Mary

Sat Oct 13 2012, 05:45PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

This is a marvellous project, Radhu, really very good!

Just in case you thought I was asleep, you have made a little capacitor - 3pF at a guess - between the black and white wires going to the GM tube, but it would only become significant at the very high counting rates I hope you will never experience around your home.

radhoo

Sat Oct 13 2012, 09:42PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Indeed it is preferred to shorten the wires as much as possible, and I will do that by connecting the tube's anode directly to the PCB, via a very small connector.

Proud Mary

Sat Oct 13 2012, 09:49PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Is there some reason why C7 is so large - 20 nF?

radhoo

Sun Oct 14 2012, 09:14PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

I used the scope to view the pulse shape for several values. Initially I used a smaller cap, of a few hundred picos, but I changed it in the last version. Do you have any concerns regarding this value?

Some news: I managed to successfully initiate a Tcp/ip connection from the Geiger counter to a PHP script on my blog. It's late now, but I have everything in place to start exporting data.

Proud Mary

Mon Oct 15 2012, 07:28AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

wrote ...

I used the scope to view the pulse shape for several values. Initially I used a smaller cap, of a few hundred picos, but I changed it in the last version. Do you have any concerns regarding this value?

Some news: I managed to successfully initiate a Tcp/ip connection from the Geiger counter to a PHP script on my blog. It's late now, but I have everything in place to start exporting data.

The larger the capacitor, the slower will be the rise and fall times of the pulse. I would have expected to see a capacitor of 20 - 100 pF here - but perhaps just out of habit, because it will not make much practical difference at background counting rate speeds using a single GM tube.

radhoo

Thu Oct 18 2012, 09:42PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

You're a gold mine - providing all these direct hints, many thanks for this suggestion resulting in yet another improvement.

I had added a few scope pics, to illustrate the differences in pulse length, in regards to the capacitor used:

Here are 3 sets of 3 pictures, first row is with background radiation, second is with a weak Am241 source, and third is with a Cs137 source. First column shows a signal collected with a 33pF capacitor, second corresponds to a 150pF capacitor, and third column is for the 20nF capacitor.

Update,
Sensors and microcontroller software are finally working together. This project was full of obstacles, almost every single step came with bugs and issues, but eventually my determination prevailed. Here's the data received on my server, comments added after //
id=1 // this is a simple id, in case I will build more of these devices
cip=192.168.2.153 // the local device IP obtained by DHCP - no network config required!
vol=400 // the voltage on tube
duty=74 // 7.4% inverter's duty cycle responsible of the 400V produced - used in regularization
pulses=2463 // number of pulses counted since start up
s1t=22 // ds1820 sensor, this is temperature in degrees celsius
s2t=24 // dht11 sensor, temperature in degrees celsius
s2h=75 // dht11 sensor, relative humidity
s3l=19 // photodiode sensor, luminosity
td=0 // number of days since start up
th=0 // number of hours since startup
tm=16 // numer of minutes since startup
ts=41 // seconds from startup
cpm=72 // CPM for the last 5 seconds , just for debugging purposes

absolute CPM would be 2463 / 16.6 ->148 cpm . a bit high I'd say

...
pulses=4166
th=0
tm=38
ts=11
absolute CPM: 109.63 cpm , it is getting closer to expected dose rate.

radhoo

Thu Oct 18 2012, 10:20PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Sensor board:

I made it with the 2cm little tubes, so I can mount it with the openings downside, to prevent rain from getting to the electronic components, and still keep the sensors in good contact with the air, to measure temperature and humidity.

Dose update:
pulses=7176
td=0
th=1
tm=14

CPM: 96cpm

Hope to have the chart software ready by tomorrow. I also need to build some kind of waterproof case for the entire setup.

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