Re: [TCML] Measuring Isecondary: Current transformer too close to primary?

[jhowson4@xxxxxxxxxxx]

The distances may be small, but the peak currents inside the primary are quite large. And more importantly the change in current is also quite large as it is high frequency enhancing its ability to induce voltages. 

I wonder if some mu metal foil from an old oscilloscope would serve this application, hmmm 



Thanks, 
John "Jay" Howson IV 


"Why thank you, I will be happy to take those electrons off your hands." 

----- Original Message -----
From: "Andreas Hahn" <andreas.hahn@xxxxxxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> 
Sent: Saturday, September 1, 2012 5:00:31 PM 
Subject: Re: [TCML] Measuring Isecondary: Current transformer too close to primary? 

That's a valid point -- though the transformer is quite small relative to 
the distances involved (just under 1.5cm diameter toroid, vs 5cm+ distance 
to the nearest primary lead). But yes, magnetic shielding would seem to be 
the solution... 


On Sat, 1 Sep 2012, jhowson4@xxxxxxxxxxx wrote: 

> Wouldn't the fields from the primary canceling out be dependent on those fields being uniform though? 
> 
> The primary is a spiral, so you have some non uniformity from that effect (offset circles) 
> But more probable is the primary inner lead, which would probably run "roughly" parallel to the wire coming from the base of the secondary. 
> Add on top of that the fact that primary currents are usually orders of magnitude higher than that of the secondary. 
> Seems reasonable to me that the proximity of the primary would be a major concern. 
> 
> Perhaps you can put the current transformer inside a hunk of thick iron pipe to try and eliminate some of these magnetic effects? 
> 
> 
> 
> Thanks, 
> John "Jay" Howson IV 
> 
> 
> "Why thank you, I will be happy to take those electrons off your hands." 
> 
> ----- Original Message ----- 
> From: "Andreas Hahn" <andreas.hahn@xxxxxxxxxxx> 
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> 
> Sent: Saturday, September 1, 2012 2:58:02 PM 
> Subject: [TCML] Measuring Isecondary: Current transformer too close to primary? 
> 
> Looking through the archives for current transformer theory, I found this: 
> http://www.pupman.com/listarchives/1999/February/msg00081.html 
> "I was using a current transformer and (this time) a usual scope 10:1 
> probe. 
> As I was about 40 cm from the primary, probably the magnetic field induced 
> by the primary was stronger than the field induced by the secondary base 
> lead passing through the same transformer. 
> The result was that I measured an attenuated version of the primary 
> current, NOT the secondary current." 
> 
> Is this actually possible? Since the primary windings do not pass through 
> the current transformer toroid, my understanding is that any fields from 
> the primary would cancel out, and therefore little or no influence from 
> the primary should show up in the secondary of the CT. 
> 
> 
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