Sensitivity Adjustment

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Ceres
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Joined: Sun Mar 03, 2019 11:40 am

Sensitivity Adjustment

Postby Ceres » Sun Mar 03, 2019 11:47 am

Is it’s possible to adjust the sensitivity of the counter? For instance, say I want to use a tube sensitive to background radiation but be able to variably adjust the sensitivity/CPS/M. Any easy way to accomplish this?

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mightyohm
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Re: Sensitivity Adjustment

Postby mightyohm » Mon Mar 04, 2019 9:00 am

I can think of a few ways to do this:

  • Change Geiger counter tubes based on what you are trying to measure. Tubes with a larger cross section will be more sensitive. Tubes with a thinner wall or constructed with materials that pass more and lower energy radiation (like mica windows) will also be more sensitive. Conversely, tubes like the SI-3BG are very small and have a very small cross section, so they are less sensitive than the SBM-20.
  • If you start with a sensitive tube, you can add shielding materials to make the tube less sensitive as needed. This will also change the energy levels that reach the tube, so it's not quite the same thing as changing the tube's cross section, but might be close enough.
  • Adjust the integration time in software (or in firmware, as needed) - longer integration times will yield higher counts for a given radiation level, and shorter integration times will avoid overflows at very high rates.

Ceres
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Joined: Sun Mar 03, 2019 11:40 am

Re: Sensitivity Adjustment

Postby Ceres » Tue Mar 05, 2019 1:07 pm

Thanks for the response Jeff. I am trying to use it as a source of random clocking for musical purposes and have seen it implemented this with adjustable rate by potentiometer elsewhere but I’m unsure how they accomplished this. It does not appear the module has onboard arduino or software means of doing this but I’m not a 100% sure. Do the detections appear at different voltage levels? Maybe an analog adjustable threshold detector would work in that case.

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mightyohm
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Re: Sensitivity Adjustment

Postby mightyohm » Tue Mar 05, 2019 5:56 pm

Are you trying to increase or decrease sensitivity?

Ceres
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Re: Sensitivity Adjustment

Postby Ceres » Thu Mar 07, 2019 8:32 pm

I would consider either but I think decreasing would be easier. I’m willing to choose a tube based on if it is easier to increase or decrease. In other words I am open to all avenues.

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mightyohm
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Re: Sensitivity Adjustment

Postby mightyohm » Fri Mar 08, 2019 10:20 am

Try a SI-3BG tube - it's much less sensitive than the SBM-20 and there are lots of them on eBay. Alternatively you can place some shielding around the SBM-20.

Ceres
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Joined: Sun Mar 03, 2019 11:40 am

Re: Sensitivity Adjustment

Postby Ceres » Sun Mar 10, 2019 12:50 pm

I apologize, I’m not communicating this very well. I don’t want a fixed sensitivity. I would ideally like to be able to turn a potentiometer and get faster or slower clock rates based off the same tube, the larger variation from slow to fast the better. Imagine you were using the background radiation as a variable clock source. Sometimes you want approx 1 click per minute, sometimes you want approx 70 clicks per minute but you still want the randomness of using a Geiger as the source. Does that make sense?

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Re: Sensitivity Adjustment

Postby mightyohm » Mon Mar 11, 2019 8:44 am

Now I understand what you are trying to do. Geiger tubes aren't designed to work in this way, but you can try reducing the voltage to the tube - at some point the sensitivity will start to drop off. You can try adjusting VR1, but most likely you'll have to increase R8 as well. You could replace R8 with a variable resistor (maybe a 100 ohm potentiometer) and see if this achieves the effect that you are looking for.

Ceres
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Joined: Sun Mar 03, 2019 11:40 am

Re: Sensitivity Adjustment

Postby Ceres » Wed Mar 13, 2019 6:44 am

I will try that. Thanks so much for your input and patience!


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