uRADMonitor - Online radiation monitoring station

[radu.motisan]

Ok, now it's raining. Dose jumped to 0.13uSv/h . Will it stop here?

[MS3FGX]

Excellent project and stellar documentation. Definitely a very worthy cause as well, a distributed network of such sensors could provide some very interesting data.

With recent events such as Fukushima, it's obvious the public needs a reliable way to ascertain the risk of radiation without blindly accepting whatever the authorities are claiming.

[radu.motisan]

Yes, it's a good tool to keep an eye on the actual radiation level. I do have plans for building a distributed network. As I can't build a large number of devices myself, I plan to offer the entire details online, so other enthusiasts can easily implement this dosimeter. I can offer the source code, and the server side component to centralize all the data.

At this point I'm happy to see how stable it runs : despite the random desintegrations , the ambient dose debit is nice and stable at the 0.12uSv/h value. This shows the electronics perform as expected.

[radu.motisan]

Another update, 3.3.130:

SERVER:
- added new graphs: pressure (bmp085) and temperature 3 (bmp085)
CLIENT:
- dht11 sensor replaced with dht22
- bmp085 sensor added
- new sensor PCB board
- new sensor board sun shield
- additional code for the new sensor and i2c bus connectivity
- atmega168 replaced with atmega328p

Moving from the mega168 to 328p was smooth, with no issues. A little problem is with the previous Humidity data, recorded with DHT-11, that seems to have a different scale than what I am getting from the DHT-22.

Circuit diagram, 3.3.130


The new BMP085 sensor temperature data:


And the BMP085 pressure data, in Pascals:

[radu.motisan]

The device attracted considerable local attention and got to a few newspapers, and I even got an invitation to a TV show, where I had the chance to present some of the details behind uRadMonitor.
http://www.youtube.com/watch?v=OhuANUFjQc8
(Video is in Romanian)

I might need to improve this project even further, including the energy compensation of the tube, higher volume detector, and proper calibration.

[radu.motisan]

I'm proud to announce this update, Project featured on the HackAday front page: http://hackaday.com/2012/12/07/online-r ... g-station/

Thanks guys, yet another motivation for me to make it even better.

The last few days have indicated that rain does raise the dose, because of Radon washout.

Also we're now getting into winter's negative temperatures, so this is the first negative range test for my temperature sensors, except testing them in my fridge, back in octomber.

[radu.motisan]

There have been two anomalies in the radiation readings.

First, January 31, 2013, lasted for 7 minutes, and reached a maximum of 3781 cpm, compared to the normal average value of 81.

The last one happened this night, February 08, 2013, lasted for 8 minutes (strange similarity), and reached a peak of 5175cpm.

The debug data for both , shows normal system functionality, including the voltage measured on the geiger tube, which remains in normal parameters during these events. The other sensors (3x temperature, 1x humidity, 1x barometric pressure, 1x luminosity) show normal readings.


<b>Debug data</b> for the first is available here: http://www.pocketmagic.net/2013/01/urad ... ts/#130131


Debug data for the second event is here: http://www.pocketmagic.net/2013/01/urad ... ts/#130208

Wish I knew what was happening. I plan to add an alarm feature to the monitor station, since the events last for considerable time, I can just use my other equipment to take measurements, but also add a second backup/redundant detector to the monitor station.

Any other suggestions?

[radu.motisan]

I have attached the maximum resolution charts, built with the data I have. What's interesting is that temperature has increased during the event with 0.5 degrees. Keep in mind that the peak happened during a cold winter night, with no sources for additional heat: except perhaps a little extra radiation, passing a bit of its energy to the air, as heat? All three temperature sensors running in parallel have recorded an increase:

February 8, 2013:

1cpm.png (84.96 KiB) Viewed 378 times

2temp1.png (70.88 KiB) Viewed 378 times

January 31, 2013:

3cpm.png (56 KiB) Viewed 378 times

What's strange is that the anomalies have the same shape and time length.

[radu.motisan]

The recent atypical measurements raised a few questions on the nature of the events: malfunction of the detector (specifically the Geiger Tube due to age) or a legitimate manifestation of a radiation phenomenon: http://www.pocketmagic.net/2013/01/urad ... n-reports/
Some bits of additional info, even if redundant, should share some light on the Geiger detector, as used in the uRADMonitor system. For a start, here is the current circuit diagram:

The R7 10M anode resistor is a quality component, mounted correctly without fingerprints, dust or humidity. Should this resistor malfunction in any way, one result could be avalanche discharges in the Geiger tube. This resistor has been checked recently and it meets the requirements.
Resistor R5 is used in a voltage divider , by the microcontroller to continuously measure the voltage across the Geiger tube, using one of its ADC (analog to digital) ports. In just a few words, for 400V set on the tube, the voltage divider will return 3.96V ( 400V x 47/(4700+47) ). The micro-controller is set to use a relative voltage of 5V (Vref). The ADC port that measures the tube voltage, has a resolution of 10bits, so for a maximum of 5V on PC3/ADC3, the software would read the max value of 2^10 = 1024. For 4V we would get the proportional value. By doing so, the measurement of the anode voltage is extremely precise.
Should the voltage on tube be lower than the preset threshold (400V), the duty cycle factor of the inverter's PWM is increased, in small steps, until we reach the target voltage (in a given tolerance, initially set to 5V and now changed to 2V). If the voltage on the tube is too high, we do the opposite and decrease the duty factor. In a few words, this is a known regularization mechanism that works well, fact confirmed by the logs, showing several months of constant voltage tube values.
Some time ago, there was an issue with R5: After some use, it "burned" and got interrupted. As a result, the voltage measurement could no longer be done, and the software saw the voltage on tube as being 0. As a result, the duty cycle began to rise, resulting in uncontrolled high voltage generation, way above the tube's safety limits. Luckily, this high voltage also resulted in microcontroller temporarily failure, and so the PWM generation stopped . This in turn, also stopped the dangerous voltage from being applied to the tube (except for the first few miliseconds). R5 has been replaced with a better quality resistor.
I was recommended the following useful resources:
1. An investigation into the causes of short lifetimes of geiger-muller tubes used in aircraft oil gauging systems
2. Test Procedure for Geiger-Mueller Radiation Detectors
3. Geiger Mueller Counting
This valuable resources are a must-read, proving their utility especially for understanding failure causes that can result in avalanche discharges and erroneous readings . Because of the recent atypical radiation measurements recorded by uRADMonitor, I need to evaluate every possibility including a malfunction of the tube.
Test Procedure for Geiger-Mueller Radiation Detectors (2), proposes a 15% slope as the cut off between good and bad tubes: "In general, the value of the slope must be less than 15 % to consider that the detector is in good conditions." This seems to be a very large figure when you think of really good new GM tubes having plateau slopes of less than 3%.
I ran a few measurements with the current setup. SBM-19's operation interval is 350-475V. For my particular tube, I got unsatisfactory readings for 350V, but good performance in the 375-450V interval, despite its age.
The measurements has been performed during several hours, to acquire sufficient data for computing average values.
Voltage on tube / CPM (with natural background radiation)
349.33 / 65.88
375.64 / 78.62
399.65 / 79.98
424.71 / 80.18
449.51 / 79.68
Complete measurement details in attached PDF document:

sbm_19.zip

(81.17 KiB) Downloaded 13 times

To test the tube's performance indicator as presented in "Test Procedure for Geiger-Mueller Radiation Detectors",
I set N1 = 78.62 , V1 = 375.64V , N2 = 79.68 and V2 = 449.51V
For P = 100 * ((N2 - N1)/(V2-V1)) * (100 / ( (N1+N2) / 2)) we get: 1.81060853% much under the 15% limit proposed in the paper.
The device has been set to 375V (in software), as compared to 400V used from October 2012 until now.