What is the best method to measure spark gap frequency? / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

What is the best method to measure spark gap frequency?

1 2 next

Move Thread

LAN_403

ifryd

Mon Mar 05 2012, 05:16PM

Registered Member #4215 Joined: Wed Nov 16 2011, 09:45PM
Location:
Posts: 32

Hello

I want to measure frequency of impulses of the current passing during the discharge of the capacitor. I know subject was described here but I would like to clarify few things:

http://4hv.org/e107_plugins/forum/forum_viewtopic.php?130915.post

Basically I thought about four options applying to my project:

a) detection by microphone
b) Hall effect sensor
c) direct method basing on voltage measurement across wire
d) light sensor next to spark gap

Now question is which solution would be the best? What do I need?

Is hall sensor capable of measuring current impulse of ten nanoseconds?

What solution would be the easiest to apply and the most reliable? Do you have any experience with measuring spark gap frequency?

Adam

Hall effect sensor + low pass filter + impulse width expander ?

Carl Pugh

Mon Mar 05 2012, 05:32PM

Registered Member #1064 Joined: Tue Oct 16 2007, 05:04PM
Location:
Posts: 42

Have you tried holding oscilloscope probe up in the air with probe not connected to anything.

Proud Mary

Mon Mar 05 2012, 08:13PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Rogowski coils are sometimes used as current transducers in the nanosecond regime - but first you have to create the 10 ns discharge you want to measure!

Forty

Tue Mar 06 2012, 03:15AM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

Battery + photodiode + oscilloscope would probably work well. That's the method I used to measure the rpm of a rotating mirror with a laser bouncing off it (for the Foucault method of measuring c)

ifryd

Tue Mar 06 2012, 12:47PM

Registered Member #4215 Joined: Wed Nov 16 2011, 09:45PM
Location:
Posts: 32

Rogowski coils are sometimes used as current transducers in the nanosecond regime - but first you have to create the 10 ns discharge you want to measure!

Yes I think Rogowski coil is a way to go! Thank you... As far as I see it is simple coreless coil with integrator. I wonder if this single first loop is necessary and how it influence output signal?

Proud Mary

Tue Mar 06 2012, 03:14PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Here is a paper that may give you some ideas. It won't accept direct links, but if you Google

"Design of a current transducer with a magnetic core for use in measurements of nanosecond current pulses"

you will go straight to it, and can download it free in pdf.

It looks quite involved, but I find that there's always something you can take away and use in even very difficult papers, that makes them worth reading.

If you're prepared to sacrifice having a time resolution quite so short as 10 nanosecs, then I think Forty's simple optical solution would suit most people's needs.

I don't think the circuit you've shown up top could produce such short pulses as it is. You have a 0.5Î© resistance in series with your gap, so what must the total circuit capacitance be (including gaps etc) to have a time constant of 10 nanosecs? (Ï„ = RC)

Tip: the secret of getting pulse sharpening gaps to work is to massively overvolt them.

teravolt

Tue Mar 06 2012, 05:20PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

curent transformer

ifryd

Tue Mar 06 2012, 09:29PM

Registered Member #4215 Joined: Wed Nov 16 2011, 09:45PM
Location:
Posts: 32

Thank you Proud Mary for the great article. Your posts are very informative.
Let me quote one thing from the article:

Pellinen et al consider that if the time
constant Ls/R in the equivalent circuit is shorter than the pulse
width of the primary current, the current transducer acts as
a â€˜differentiating coilâ€™ with the disadvantage of frequency
dependence; in the opposite case, it is a â€˜self-integrating
coilâ€™ with the advantage of frequency independence [4].

whole article:

I think all about Rogowski coil is that it is self integrating coil which is beneficial for observing high pulse discharges.

For the detection of discharges it would be easy to use photo-diode but few things are not clear for me.
For example how strong is light from spark gap and will it polarize diode enough? Of course it would be the best to test it in laboratory,
Also I wanted to put there strong magnets for quenching so I don`t know if I find place for diode...
Anyway these two options are simple to apply and I think one can get good results from using them.

If we talk about time discharge of course time depends from (T=RC).
I also doubt I could get from my circuit discharges of 10ns. Anyway as far as I remember from literature spark gaps can trigger with maximum time of about 9ns. That`s why I wrote maximum possible time for spark gap.

To sum up:

a) detection by microphone (can be slow and harder to apply)
b) Hall effect sensor (can be slow)
c) direct method basing on voltage measurement across wire (protective problems)
d) light sensor/ detector next to spark gap (easy to apply)
e) Rogowski coil (self integrating accurate coil)

BTW.
If you want to put link delete from it "hyperlink url". I found it helps for me otherwise links don`t work.

teravolt

Tue Mar 06 2012, 10:41PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

did you want to see the pulses and there content or ere you trying to tune your tesla

ifryd

Tue Mar 06 2012, 11:12PM

Registered Member #4215 Joined: Wed Nov 16 2011, 09:45PM
Location:
Posts: 32

I just wanted to measure frequency of the firing spark gap. I don`t know how much power I will get from my fly-back transformer and what will be the frequency of discharging capacitor through spark gap...

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob