Author Topic: Geiger Counter Pulser Circuit  (Read 6673 times)

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Offline dexters_labTopic starter

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Geiger Counter Pulser Circuit
« on: March 05, 2015, 09:58:54 am »
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?

Offline SeanB

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Re: Geiger Counter Pulser Circuit
« Reply #1 on: March 05, 2015, 07:14:36 pm »
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.
 

Online Fraser

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Re: Geiger Counter Pulser Circuit
« Reply #2 on: March 05, 2015, 11:20:37 pm »
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.
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Offline dexters_labTopic starter

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Re: Geiger Counter Pulser Circuit
« Reply #3 on: March 06, 2015, 08:26:51 am »
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

Offline dexters_labTopic starter

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Re: Geiger Counter Pulser Circuit
« Reply #4 on: March 06, 2015, 09:24:02 am »
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?

Online Fraser

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Re: Geiger Counter Pulser Circuit
« Reply #5 on: March 06, 2015, 03:52:29 pm »
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 06, 2015, 03:57:30 pm by Aurora »
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Offline vindoline

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Re: Geiger Counter Pulser Circuit
« Reply #6 on: March 06, 2015, 05:32:21 pm »
There are some additional circuits here: http://www.qsl.net/k/k0ff//0%20GEOelectronics%20KITS/Pulsers/
 

Offline dexters_labTopic starter

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Re: Geiger Counter Pulser Circuit
« Reply #7 on: March 06, 2015, 07:33:33 pm »
awesome, i am sure i'll have something working from that lot

Offline dexters_labTopic starter

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Re: Geiger Counter Pulser Circuit
« Reply #8 on: March 11, 2015, 03:59:19 pm »
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


Online Fraser

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Re: Geiger Counter Pulser Circuit
« Reply #9 on: March 11, 2015, 05:21:47 pm »
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 11, 2015, 05:24:37 pm by Aurora »
If I have helped you please consider a donation : https://gofund.me/c86b0a2c
 

Offline dexters_labTopic starter

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Re: Geiger Counter Pulser Circuit
« Reply #10 on: March 26, 2015, 11:13:38 am »
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?

Offline vindoline

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Re: Geiger Counter Pulser Circuit
« Reply #11 on: March 26, 2015, 11:56:22 am »
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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