Geiger Counter Pulser Circuit - Page 1
Forum section: electronics / beginners

author: dexters_lab
author_rank: Unknown
timestamp: March 05, 2015, 09:58:54 am
content: 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=specificationsMine 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.pngIdeally, 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 oncan anyone offer any help or advice?

author: SeanB
author_rank: Super Contributor
timestamp: March 05, 2015, 07:14:36 pm
content: 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.

author: Fraser
author_rank: Super Contributor
timestamp: March 05, 2015, 11:20:37 pm
content: 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

author: dexters_lab
author_rank: Unknown
timestamp: March 06, 2015, 08:26:51 am
content: thanks guysi 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

author: dexters_lab
author_rank: Unknown
timestamp: March 06, 2015, 09:24:02 am
content: ok just found this...from about 3/4 the way down the page here the author describes the circuithttp://www.techlib.com/science/geiger.htmlso 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?

author: Fraser
author_rank: Super Contributor
timestamp: March 06, 2015, 03:52:29 pm
content: http://www.qsl.net/k/k0ff/01%20Manuals/Mini%20Instruments/MINI-MONITOR%20900%20With%20Scintillator%20Probe%20Version/Mini+900+Scint.pdfNote comment regarding paralysis time correction. It is different for scintillator probes and Geiger Muller tubes.Aurora

author: vindoline
author_rank: Unknown
timestamp: March 06, 2015, 05:32:21 pm
content: There are some additional circuits here:http://www.qsl.net/k/k0ff//0%20GEOelectronics%20KITS/Pulsers/

author: dexters_lab
author_rank: Unknown
timestamp: March 06, 2015, 07:33:33 pm
content: awesome, i am sure i'll have something working from that lot

author: dexters_lab
author_rank: Unknown
timestamp: March 11, 2015, 03:59:19 pm
content: ok, so i am just waiting for a few components to arrivejust 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 abouthttp://www.qsl.net/k/k0ff//0%20GEOelectronics%20KITS/Pulsers/Robert%20G8RPI%20Pulser%20Info/G8RPI%20Pulser%202013(1).pdf

author: Fraser
author_rank: Super Contributor
timestamp: March 11, 2015, 05:21:47 pm
content: 0V to 6V clock signal output from CMOS ICResistive Divider with variable element (potentiometer) to set output level (normally set to approx 1 Volt)Capacitive coupling to voltage limiter (diode)Capacitive coupling tohigh voltageoutput (and signal input) of Geiger counter.OK ?This circuit takes no account of Paralysis or Dead time.Aurora

author: dexters_lab
author_rank: Unknown
timestamp: March 26, 2015, 11:13:38 am
content: 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?

author: vindoline
author_rank: Unknown
timestamp: March 26, 2015, 11:56:22 am
content: 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