radiation meter November 2011

Equipment, circuits, projects, procedures

Postby arto » Thu Aug 01, 2013 12:00 am

I think improved radiation meter is so unsensitive than man dies
to radioactive radiation before it shows anything ...

I'm very unsatisfied that I spend my money to that humbug

It was too good to be true

It's only value is rubbish...

It simply do not work
'
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Postby thijsbeckers » Thu Aug 01, 2013 12:00 am

I'm sorry to hear you are disappointed.

We have tested our circuit and several sensors at the Nuclear Physics Laboratory of the University of Namur, Belgium (see page 44 in our October 2011 edition - Verification of radiation meter), and the BPW34 proved usable as a sensor. We used 137 Cs with 661 keV Gamma. We also tested a BPX61 with 244 Cm, 5.8 MeV Alpha and 239 Pu, 5 MeV.

This design is excellent for testing various silicon based semiconductors for suitability as a radiation sensor. We provided a single BPW34 as the sensor, but you could, as you probably read on our forums, also experiment with multiple BPW34's, or the trusty old 2N3055.

So it depends on your application/what you want to do with it, but we were able to detect static background radiation from the environment with the BPW34...'
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Postby johnneyboy » Mon Sep 02, 2013 12:00 am

Hello,

I have just built one of the new sensors, sadly it is not counting. Have tried changing the 'level', no difference, over about 15 minutes.

The voltage on pin 2 of the op amp is approx 5.6v.

I have also noticed that if I try to measure the voltage on the sensor, I know this may not be possible due to the high values of the resistors, it starts to count, whilst the probe is placed and removed, this is true for both pins of the sensor.

I have yet to place it in a metal light prof box, but for initial testing in a light prof container, not metal.

My Scope packed up yesterday, so can't have a look at any points Old Techtronics 475

Regards John
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Postby thijsbeckers » Mon Sep 02, 2013 12:00 am

Looks like the uC is working for sure.

It's hard to tell without having the circuit on my desk, but it looks very much like the symptoms I encounter when the sensor/detection circuit is being overloaded. Since the amplification factor of the preamp is so ridiculously high, it is very much prone to this. It happens when the sensor is hit by light and/or when the amp circuit casing isn't grounded properly. I suggest you take care of that first.

Quick & dirty: wrap the amp circuit in thin plastic foil (to prevent short circuiting it) and then in aluminum foil. It doesn't need to be a stronghold! Just a single sheet should suffice (make sure you don't have the aluminum foil with small holes in it!). Ground the foil!
This should let you be able to count background gamma radiation (0.33 cpm).

Good luck!
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Postby johnneyboy » Tue Sep 03, 2013 12:00 am

Hello,

I have wrapped the sensor/opamp circuit in tape, sticky side out. The put aluminium foil around it, and connected it to the ground 0v of the psu. Well from not detecting anything it has gone mad, thousands of hits per second, so how am I still alive and I do not live at Fukushima or Chernobyl

Any ideas?

John
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Postby thijsbeckers » Wed Sep 04, 2013 12:00 am

. Youre getting there...

There's still a few things that could cause this. Is the circuit near fluorescent lighting? Near an old CRT monitor? Phone next to it? Et cetera.

At what level is the threshold?

To bad you can't put up a scope image. That would've made it easier.

BTW, are you 100% sure the alu-wrap is shielding ALL the light from the sensor? And that is is grounded properly (what's the resistance from foil to ground?)

What happens if you turn of the lights? What happens if you touch the shielding (or let go of it)?'
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Postby kibt » Thu Sep 19, 2013 12:00 am

Hi,

Thanks for being available to convene this forum. You've been given a tough job.

I've had the usual noise problem and finally sorted it. Yes the sensor amplifier is very sensitive, far more sensitive than expected. It might make a good photomultiplier sensor (if elektor is keen to go down that path). Given the number of people who have built the device it might be good to put together a follow up article that addresses the main concerns. Now than I have managed to get my device working. I'm moving onto the next issue. I'm happy to put up with around 100mV of noise and decided that this noise level could be compensated by software. The comparator seems to be doing what it is supposed to do - identifying the threshold for the noise, which is at 15 (slightly more than the default). However, during the count it changes anywhere from 20 to 90. I would expect the threshold to stay constant after the initial trigger threshold setting. This is not what I would expect. I'm able to talk to the chip through an rs232 interface so I'm theoretically able to modify the program. Do you have a program listing complete with comments? Plus I might start fiddling with the amplifier to change the sensor threshold prior to software. Is this a good idea? One last question, is it possible to log the response from the atmega88 to look at what its reading. Or does this present too much data?

regards

kibt
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Postby thijsbeckers » Thu Sep 19, 2013 12:00 am

Hi kibt,

Thank you for your sympathy .

kibt... during the count it changes anywhere from 20 to 90.

Thats odd. I've never seen that happening! It should stay at a constant value, as you initially set it. Could there be some sort if interference that's messing with your RS232 connection? Does it still happen if you disconnect the RS232 connection?

kibtI might start fiddling with the amplifier to change the sensor threshold prior to software. Is this a good idea?

Let me know the outcome and I'll tell you if that was a good idea .

kibtOne last question, is it possible to log the response from the atmega88 to look at what its reading. Or does this present too much data?

The sensor data' is available from K4 and the uC is just counting pulses, so I'm not sure what you'd like to accomplish?

Cheers.'
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Postby thijsbeckers » Fri Oct 04, 2013 12:00 am

Hi chllmanthe3,

We started selling kits and modules as a service to our readers. So we assumed whomever bought a kit surely has read the accompanying article and knows up front what they're getting themselves into . But lately more and more customers who have never even heard of the magazine are finding and buying our kits' (the term 'kit' is perhaps a little misleading, 'semi-kit' would cover the contents more accurately).
So we are now posed with the problem that we don't write (construction) manuals for our products. Though the accompanying article (Elektor Magazine November 2011, www.elektor.com/110538) is a nice read and describes the circuit in detail (including schematics), it is by no means a construction manual.
This has been acknowledged and we are now entering the process of reconstructing our ways of working in order to be able to produce and offer proper kits. We still have a long way to go, we're magazine editors, not construction manual writers, so you'll have to excuse us if there are some loopholes with some of our future products.
Also, I don't think we're going to go through the time-intensive process of writing construction manuals for all the existing kits. We simply don't have the manpower to pull that off.

Back to your question. I'm sure that this project, the Improved Radiation Meter, is not too hard to put together. It's all through hole and if you've held a soldering iron once before it's really no big deal. Just make sure you put everything where it belongs (component names are printed on the PCB and the component list can be found on line at the article page I mentioned above, tab 'Components') and don't mess up polarities and the orientation of the IC's. Of course it would be easier and clearly organized if you had the article, which you had if you where a member .
I assume you know its good practice to start with soldering the components with the lowest profile (like resistors) before soldering the higher profile ones?
And lastly, don't hesitate to come back if you have any questions. Hundreds (literally!, we sold more than a thousand kits) have gone before you and we received hardly any complaints...

Good luck and happy soldering!

Cheers!

Thijs'
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Postby chllmanthe3 » Fri Oct 04, 2013 12:00 am

I have a 110538-71 kit.
It has no documentation other than the LCD backlight notice mentioned earlier in this forum.

Is there any assembly instructions or schematics available?
Do I have to buy an "Article PDF" to get info on this, or is there another source?

Thanks so much for your help.
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