Author Topic: Geiger Counter Pulser Circuit  (Read 4142 times)

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Offline dexters_lab

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Geiger Counter Pulser Circuit
« on: March 05, 2015, 08:58:54 pm »
one of my geiger counters has an analog meter scale and is calibrated in uRontgen for use with it's specific geiger tube, i would like to change the scale face to read in CPM (Counts Per Minute) so i can use it with any tube.

Means i need to connect something up to the GM tube input on the meter and simulate a GM tube and pulse it, increasing in frequency until it goes full scale on the analog meter so i can plot out a new scale in CPM.

These devices are called pulsers and are commercially available, but just dont ask how much they cost:
http://www.ludlums.com/component/virtuemart/pulse-generator-29-detail?activetab=specifications

Mine does not need any kind of voltage readout, pulse amplitude or anything fancy like that.

you can see a typical HV drive / detection circuit on the mighty ohm counter schematic here:
http://mightyohm.com/files/geiger/geiger_sch_fixedR5R6.png

Ideally, i would like this to go upto 400-500khz so i can use it with my current ludlum too (which peaks out at 420,000CPM on it's current x100 scale)

i do have a rather poxy function gen i could use or i could write some code for a uC to provide the signal, it's just the driver circuit to actually pulse the GM input i need help on

can anyone offer any help or advice?
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Offline SeanB

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Re: Geiger Counter Pulser Circuit
« Reply #1 on: March 06, 2015, 06:14:36 am »
Simplest would be a resistor to load down the voltage somewhat so the PSU does not kill itself, then a simple capacitive pulse coupling to the input from the pulse generator, with a series 1k resistor. The high voltage resistor will need a separate ground connection, and you just use a 5-10V pp signal from the function generator, preferably with the pulse width adjusted to give a narrow positive pulse.

10M high voltage resistor as load, and a 100n in series with 1k as simulation side. That should be good enough for most tubes.
 

Offline Fraser

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Re: Geiger Counter Pulser Circuit
« Reply #2 on: March 06, 2015, 10:20:37 am »
As SeanB has explained, this is a common test done on such units. If you Google for Mini Monitor 900 you will find the user manual that also includes the exact process to input a function generator signal for testing purposes.
Aurora
 

Offline dexters_lab

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Re: Geiger Counter Pulser Circuit
« Reply #3 on: March 06, 2015, 07:26:51 pm »
thanks guys

i have googled and googled but any kind of user or service guide for the mini 900 is proving elusive, though in the process i did find details on what looks like a later version of the Mini Instruments 6-70 unit i did a teardown on a few months back, including details on its probe, which is handy!

If you have seen the manual somewhere that had a typical setup for doing this without the purpose build pulser, can you send me the linky?

either way, it looks like i will need a proper function gen, what i have just isn't going to cut it
"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." - Douglas Adams
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Offline dexters_lab

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Re: Geiger Counter Pulser Circuit
« Reply #4 on: March 06, 2015, 08:24:02 pm »
ok just found this...


from about 3/4 the way down the page here the author describes the circuit
http://www.techlib.com/science/geiger.html

so if i took everything to the right of the 2.2nf cap i should be able to drive this with a pulsed output from a uC?
"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." - Douglas Adams
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Offline Fraser

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Re: Geiger Counter Pulser Circuit
« Reply #5 on: March 07, 2015, 02:52:29 am »
http://www.qsl.net/k/k0ff/01%20Manuals/Mini%20Instruments/MINI-MONITOR%20900%20With%20Scintillator%20Probe%20Version/Mini+900+Scint.pdf


Note comment regarding paralysis time correction. It is different for scintillator probes and Geiger Muller tubes.

Aurora
« Last Edit: March 07, 2015, 02:57:30 am by Aurora »
 

Offline vindoline

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Re: Geiger Counter Pulser Circuit
« Reply #6 on: March 07, 2015, 04:32:21 am »
There are some additional circuits here: http://www.qsl.net/k/k0ff//0%20GEOelectronics%20KITS/Pulsers/
 

Offline dexters_lab

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Re: Geiger Counter Pulser Circuit
« Reply #7 on: March 07, 2015, 06:33:33 am »
awesome, i am sure i'll have something working from that lot
"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." - Douglas Adams
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Offline dexters_lab

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Re: Geiger Counter Pulser Circuit
« Reply #8 on: March 12, 2015, 02:59:19 am »
ok, so i am just waiting for a few components to arrive

just so i'm not blindly making something can someone explain how the circuit works?

i understand the divider, crystal etc generating the different clock outputs, it's more the section from the divider to the GM input i'm interested in learning about

http://www.qsl.net/k/k0ff//0%20GEOelectronics%20KITS/Pulsers/Robert%20G8RPI%20Pulser%20Info/G8RPI%20Pulser%202013(1).pdf

"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." - Douglas Adams
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Offline Fraser

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Re: Geiger Counter Pulser Circuit
« Reply #9 on: March 12, 2015, 04:21:47 am »
0V to 6V clock signal output from CMOS IC
Resistive Divider with variable element (potentiometer) to set output level (normally set to approx  1 Volt)
Capacitive coupling to voltage limiter (diode)
Capacitive coupling to high voltage output (and signal input) of Geiger counter.

OK ?

This circuit takes no account of Paralysis or Dead time.

Aurora
« Last Edit: March 12, 2015, 04:24:37 am by Aurora »
 

Offline dexters_lab

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Re: Geiger Counter Pulser Circuit
« Reply #10 on: March 26, 2015, 10:13:38 pm »
might need a bit more help with this, i built up everything from that schematic from S2 to the right. The pdf mentions VR1 can be a fixed 1k if no pulse height control is needed so thats what i used.

I dont have a clock source just yet, that would have been my next step after checking this works. So i am just trying to get this to work and nothing, i take it i should just be able to pulse 6v or so into R3?
"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." - Douglas Adams
http://www.youtube.com/user/DextersLab2013
http://dexterslab2013.blogspot.co.uk/
 

Offline vindoline

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Re: Geiger Counter Pulser Circuit
« Reply #11 on: March 26, 2015, 10:56:22 pm »
If you have, a simple function generator, you can just inject a square wave into R3 and you should get a small pulse at the output
 


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