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Registered Member #2273
Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37
Hey guys,
I am building a Geigercounter with this shematic:
Because I get bored of the tack-tack-tack in the speaker, i want to connect the Geigercounter to a counter decade with the cd4026. This device makes allready a great job. But the problem is: Where do I connect the counter input to the geigercounter himself? Do I need another device between them?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Hello Philip,
I would suggest using an AC-coupled Schmitt trigger to square up the pulses, and eliminate noise, before passing the conditioned data on to the next stage.
I have not been able to find 74315 in the LND catalogue, and wonder if an error has got in somewhere.
Registered Member #2273
Joined: Thu Aug 06 2009, 07:02PM
Location:
Posts: 37
Hello,
I am not using the LND 74315 but this one here: It's fine for alpha radiation, it has a nice mica window.
And i think i fixed the problem: I hooked up the counter input to the collector of T1 in the schematic. But i have some other Problem now. When I use a 3 stage multiplier as in the schematic the speaker is klicking very fast, also without any radioactive source. But with every klick the counter counts 1 higher. When I scale down the multiplier to 2 stages I have one klick in about 8 seconds. (which is caused by the cosmic radiation i guess) But the voltage at the output is to low for that the counter unit reacts. I mean you can here a klick, but the counter don't counts.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
hv-friekie wrote ...
When I use a 3 stage multiplier as in the schematic the speaker is klicking very fast, also without any radioactive source.
The LND 712 recommended operating voltage is 500V, but your circuit diagram shows 1kV being fed to the anode. This over-voltage will produce uncontrolled avalanches, and continuous conduction which will damage the tube.
As for your counting problem, I have suggested that you condition the output pulse from the tube with a Schmitt trigger to make the pulses more compatible with digital circuits.
LND 712 is a miniature stainless steel tube designed for dosimetry and radiological protection - it has been made so that it will not be too sensitive and cause false alarms. The sensitivity of a GM tube depends, in part, on the volume of the gas it contains, and there isn't much gas in a 712 which has an effective length of 38.1mm and an effective diameter of 9.1mm. The bigger the tube, the more of it there is for particles and rays to hit.
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Problems with Geiger-counter
