Deadtime in Geiger Muller Tubes

[andreacos]

articolo Deadtime in Geiger Muller Tubes - George Dowell.pdf

[cmug]

Hello
I wan’t to examen the deadtime of my SMB-20 GM-tube
I read about the two source method. ([External Link Removed for Guests]) But difficult to do at my home because I have no good measurement equipment and I have not two good sources to investigate this.
I read (most of the time in theory) that you can measure deadtime also with an oscilloscope.
That seems more easy. So I tried. For SMB-20 datasheet : deadtime 190µs
But I found circa 3 µs
Did not find an good practical explanation how to do this. So I've come up with a measurement setup myself.
This circuit I used (end of this text)

My results:
Voltage 0,2 V /div (1:10 probe) ; Time base: 1 µs/div
I measure —>> V piek = 10 Volt and pulse width circa 3 µS
For SMB-20 datasheet : deadtime 100µS

What did I do wrong that I get so different figures compare to datasheet ?

(sorry I'am from The Netherlands and I can't write Italian, but I know lots of you can read my question in English)

[eliocor]

You are measuring the pulse width, not the dead time....
Please take a look at the following document (NIST): [External Link Removed for Guests]" onclick="window.open(this.href);return false;
and to figure 2: you can see that a new pulse can happen only after some time a previously pulse has happened.
A similar picture can be found at: [External Link Removed for Guests]" onclick="window.open(this.href);return false;

Some other (maybe) interesting links:
[External Link Removed for Guests]" onclick="window.open(this.href);return false;
[External Link Removed for Guests]" onclick="window.open(this.href);return false;
[External Link Removed for Guests]" onclick="window.open(this.href);return false;
[External Link Removed for Guests]" onclick="window.open(this.href);return false;
[External Link Removed for Guests]" onclick="window.open(this.href);return false;

myers1956.pdf

[marconmeteo]

Perfect, eliocor was faster (and more complete than me) to respond, so take a good read to references that indicated you.

[cmug]

Grazie mille
Thanks for your fast replay. I already start with reading the artikels.
What strikes me, incidentally, that nowhere in the artikels is shown how you connect the oscilloscope (with a real electric diagram).
With High Voltage and relative low input impedance of an scope, you make fast an mistake.
OK my interpretation of the scope image is certainly not good.
Later I do same measurement with my oscilloscope on my computer.

[eliocor]

Please take a look also to the attached document (which strangely enough, it reminds me some other alien posts...*)

*) wink wink nudge nudge... say no more, say no more!

[cmug]

Thanks again for al the information you've send (I have not read it all yet, to many)
But after reading an part, I think I knew what to do, and looked for other settings on my oscilloscope.
Think I did now the right measurement.
And found on my new scope the persistence mode. The Scope displays a single, modified scope view in which old waveforms remain on the screen in faded colors while new waveforms are drawn in brighter colors.

Now I get an image like I found on [External Link Removed for Guests] (page 26) or on [External Link Removed for Guests]
See the White scope drawing on Attachement
and
I measure now ~ 190 µs ; what is the same of the datasheet.
Black screen picture from scope: This is my scope image ( horizontal 200 us / div )

[marconmeteo]

Hi cmug, very good work !!

[cmug]

Grazie!

[cicastol]

Knowing GM dead time it's not really useful , you need to know the resolving time, this take accounts for all variable such supply voltage,anode load resistor, stray capacitance of the coaxial cable ecc.
The only method is the two source.