Oscilloscope for watching discharges / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

Oscilloscope for watching discharges

Move Thread

LAN_403

Neil

Mon May 05 2008, 07:48PM

Registered Member #1458 Joined: Wed Apr 30 2008, 09:47AM
Location:
Posts: 51

I have seen how some people use oscilloscopes to watch their discharges to see peak amps and the voltage reversal. Im interested in purchasing one and would like anyones thoughts on what to look for and what to stay away from. I have seen one on ebay that is 20 mHz and dual channel and it seems reasonably priced, the model number is YB4328, is this any good?. Also, does anyone have suggestions about the best way to wire up the sensor and how they go about callibrating it. My bank is 5000 volts. Thanks.

Neil.

Shaun

Mon May 05 2008, 08:16PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

For viewing single events like those in a coilgun or other launcher, you will want some sort of storage oscilloscope, analog or digital. Oscilloscopes are normally designed for viewing the exact same event repeated many times per second (thus the oscillo- prefix).

Although all analog scopes I've seen have a "single-sweep" function, all they do is flash the waveform on-screen as it happens. This is not what you want.

An analog storage oscilloscope is a regular electron beam hitting a phosphor screen, just like a normal oscilloscope. However, it has two extra devices inside so certain waveforms can be "preserved" on screen (or at least my Tek 466 does).

First, a function known as "variable persistence": An internal IR light is shined on the phosphor which causes it to glow for a longer period of time after being excited by the electron beam. This way the waveform can be preserved for several tens of seconds in my case.

Second, the "save" function: A second electron gun, called a "flood gun", shines a low-intensity beam of electrons on the entire screen. If a waveform is present, the excited phosphors in the waveform, which are positively charged, will attract that second beam and can remain readable for a long time (ive had them last over 10 minutes).
-------------

Actually catching the waveform this way will probably take a couple tries, and if you can find one cheap I would recommend a digital storage scope. The scope you mentioned is probably not a storage scope, so while you still may be able to read the waveform for the brief time its on screen, you wont catch any details.

rp181

Mon May 05 2008, 09:36PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

just wondering, how can the ocissiliscope handle such high voltage and current discharges?

Steve Conner

Tue May 06 2008, 10:48AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

It can't. You have to use voltage dividers, current transformers, Rogowski coils, etc, to reduce the signals to a level that the scope can handle safely. You'll find lots of discussion on this in other threads in the forum.

Backyard Skunkworks

Tue May 06 2008, 07:30PM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

Just got me thinking... Couldnt you use a computer sound card as a scope then? Just record the signal as audio and figure out some way to analyze it with specific voltage or current values.

Dago

Tue May 06 2008, 07:40PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

Backyard Skunkworks wrote ...

Just got me thinking... Couldnt you use a computer sound card as a scope then? Just record the signal as audio and figure out some way to analyze it with specific voltage or current values.

A computer soundcard is very slow and is not useful any any higher frequency measurements.

Barry

Thu May 08 2008, 04:59AM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

Dago wrote ...

A computer soundcard is very slow and is not useful any any higher frequency measurements.

A sound card would be limited to audio frequency sampling rates. I'm guessing that means 44 kHz or less, which is equivalent to intervals of 22 usec or longer. This can be very useful for many coilguns; my single-stage coilguns use a pulse of 1 - 5 msec.

I think you should try it and see. Just be wary of any chance for high voltage levels to leak back into your sound card. Wouldn't want to have an expensive accident.

Another option is hardware-assisted PC scopes such as the Picoscope

Good luck, Barry

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