Power quality monitor -- cheap?

On a sunny day (Thu, 22 Feb 2007 01:54:17 -0500) it happened "John Gilmer" wrote in :

There is a little catch here. The PC case is normally connected to mains ground, and we want the quality of the line between zero and phase, then without a transformer we also grab all the noise and stuff between ground and zero. That could show some peaks in some cases..

R1 |

---------------------- live --------===------------------------| soundcard line in | | [ ] R2 | |____________| soundcard ground

--------------------- zero------------ not | connected | | | PC case

--------------------- ground (safety) -------------------------|_____________

If that is your concern you didn't bring enough to the table. The primary is more like 13kv in most places.

That doesn't mean an isolation transformer "won't provide any isolation what so ever". Just that it has a voltage breakdown limit, like every other transformer and electrical device that connects to the power system. I don't know what kind of transformer your neighbor used, but there are some available with breakdown at least equal to the optoisolator that you proposed.

WIth regard to this thread, an isolation transformer serves a very significant purpose. Without it, an open neutral connection to the sensing resistors or an open resistor, would put the entire computer at line potential with respect to the earth. This could damage the mother board or something connected to it, or cause an electrocution. An isolation transformer will prevent this from happening by isolating the line voltage from the computer. If you disconnect the neutral from the transformer primary, there will be no voltage on the computer.

Ben Miller

--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com

grab

True.

If your sound card can record stereo, you can make channel 1, "Neutral" and channel 2, "Hot."

On a sunny day (Fri, 23 Feb 2007 21:41:59 -0500) it happened "John Gilmer" wrote in :

Exactly, do a differential. So then split the tracks, and substract with my substract wave program (Linux):

reload the result in a good sound editor, do a FFT.. what not. One could even listen to it ;-)

060709040709070206000101 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit

If a 4800 or 7200 V overhead crossed with the sec>>

So rent one.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

Thanks for the suggestion.

Sorry, I should have added "to build or buy, used". But I thought that was evident.

--
John English

Why not just call the power company and see if they'll loan you one?

Good Luck! Rich

Rich Grise sez:

Y'know, I never thought of that. For this one problem, it's a decent suggestion. But I'd like to have one just to rule out dirty power on a regular basis...

thanks,

--
John English

Rent one.