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uRADMonitor â€“ Online remote radiation monitoring station

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radhoo

Sun Sept 16 2012, 10:12PM

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

The current circuit diagram, version 3.3.100:

radhoo

Sun Sept 16 2012, 10:28PM

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

Update 3.3.101

I finally fixed the instability problems, the network module / PWM interference, and most of the issues I've mentioned before.
The problem was improper filtering in two key points:
1. The inverter's driver needed a little protection from those spike backs. For this I used two resistors at the inverter's driver base , and a little choke between the transformer's primary and the positive rail. This solved the spike backs:

Notice the PWM waveform still seems a little shaky at the top.
2. Voltage regulators (5V and the 3.3V), needed a few electrolytic caps

Now the PWM looks much better, and the circuit performs as expected, seems like the Ethernet module was greatly influenced by all the variations and improper filtering.
Here is the new schematic, v3.3.101:

I expect to have this ready soon, now that I'm back on track with this project :)

Proud Mary

Mon Sept 17 2012, 08:12AM

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

Circuit v 3.2

C5 and R3 shunted by P will add to the anode capacitance, and so increase dead time and tube conduction current. What is its time constant?

C6 also looks wrong to me, as it will prevent a rapid voltage rise across R4 when the GM tube conducts, and spoil the pulse shape.

Meter circuit: You may find a range switch allowing the selection of other values of C - other time constants - in the rate meter circuit will make the instrument more useful.

radhoo

Fri Oct 12 2012, 04:43PM

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

Hi Stella,

The added capacitance between the anode and ground, parallel on the tube, is indeed against all recommendations, but the Russians used it in their Kvarts-01, this being the original source for the piezzo buzzer idea, see circuit diagram on:

The resulting undesired consequences should be:
- an increase of the dead time, proportional to the time needed for the parallel capacitance to charge
- reduced tube life, because it will need to handle the discharge of the parallel capacitance as well
- multiple impulses if the parallel capacitance is reasonable big: the tube voltage doesn't drop under the quenching value, so successive ionizations are possible, thanks to the high voltage level, stored in the parallel capacitance
- modification of the plateau's geometry , including shortening the plateau length or slope increase

I have already dropped all the three components you've mentioned, because I do not need them for the digital version 3.3.x, where the goal is to have a clean, simple connection between the signal collecting point at the cathode, and the microcontroller entry pin. Feel free to check the 3.3.X diagram, but I also need to publish an update with my recent results.

Nevertheless, even with the undesired parallel capacitance, the impulses still look as expected:
Geiger Pulse 1

I'd say it's not that bad, at least on a first impression.

radhoo

Fri Oct 12 2012, 04:55PM

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

Some news. Got the new little board up an running, featuring an Atmega168 micocontroller instead of the original Atmega8, because the TCP/IP stack was already consuming 7KB of our Atmega8's 8KB total flash memory. Besides the network stack, I need to drive the HV inverter, check the HV value for regularization, count the time and the pulses, do some logic on those values, and so on... additional programming that would not fit in the Atmega8.

What should have been a simple task, since the 168 has the same pin layout like the Atmega8, ended up as a mess, wasting two days of my time. I will structure the findings and indicate the critical issues, in case others will walk this path.

In the end, it works... not yet in the final form, as I need to build charts and store the data, add sensors, and lots of bells and whistles, BUT, here is how it looks like:
Atmega168 Geiger Counter SBM19

The software computes a CPM value based on a 5seconds time constant and displays the corresponding Sieverts/Hour dose in regards to the SBM-19 Geiger tube characteristics. In red, I computed the longer-term CPM value manually.

The board is currently up and running for a stability test, and can be accessed over the internet, here. Give it a run, and let me know what you think!

Proud Mary

Fri Oct 12 2012, 06:37PM

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

Great work, Radhu!

I think perhaps you should extend the integration time when measuring very low dose rates like background <1 Î¼Sv/hr. Every time I look it is different. Maybe see how level you can keep it with 5 and 10 minute measuring cycles?

radhoo

Fri Oct 12 2012, 06:42PM

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

Hi Proud Mary, good timing! I was hoping you'll get to see the link and give it a run.

Sure, I will increase the integration time, this was made so only to make testing easier.

I have completed the work for a few sensors, that will work together with the tube: temperature, humidity and luminosity. I will add an atmospheric pressure sensor too, if it gets here in time. Curious to see what will the long term data show.

What do you think about the tube I've selected for the task? The SBM-19?

Proud Mary

Fri Oct 12 2012, 07:18PM

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

I haven't tried SBM-19 myself, but the 0.1% slope looks good, and the working voltage range makes for an easy life. If I was building a geophysical observatory, I'd run that tube directly from rectified mains voltage, and have one less thing to break down.

Geomagnetism is a very interesting property to measure in conjunction with background radiation.

Is your CPM/Î¼Sv conversion calibrated against Cs-137 or Co-60? Remember that the conversion figure will be totally meaningless below ~ 100 kV, when all GM tubes have large non-linearity of energy response. You can wrap Sn foil around the tube (or part of it) to compensate for this, but then you will have a loss of sensitivity, as you know.

radhoo

Fri Oct 12 2012, 07:33PM

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

Not yet,

Unfortunately energy response compensation is a big issue at the moment and I don't have an immediate solution for solving it. My Cs137 source is not suitable to perform such a calibration, not to mention the rest of the equipment required. So all I can do is use literature sources and put some good tips into practice.

Another option is dropping the geiger tube and using a scintillation probe instead. I'll post some interesting pics in a few minutes.

Besides the energy response compensation shield, the conversion cpm->usv/h is not a priority, since I can always build the graph using CPMs and leave the conversion to the readers. CPM data will still be valuable by itself. Another option is post-processing the CPM data provided by this device. That allows endless calculations without actually changing the detector.

Please see the picture attached. Original link:

Proud Mary

Fri Oct 12 2012, 07:49PM

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

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.

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