[time-nuts] NIST isolation amplifiers

Charles Steinmetz csteinmetz at yandex.com
Wed Nov 26 19:39:28 EST 2014

Dave wrote:

>The magnetic field in the core due to the current in the windings is 
>proportional to current times number of turns.  If there are more 
>than one winding, add the currents.  Yes, 2 x 20mA certainly exceeds 
>30mA.   The core will be driven closer or into saturation and the 
>inductance will be decreased.

Right, that's how you calculate ampere-turns.  But the question is, 
when MCL says "DC: 30mA" with no elaboration, does that mean 30mA 
through one winding, 30mA in the same direction through two windings, 
or 30mA in the same direction through all three windings?  (Whereas, 
30mA through one winding and 30mA through another equal winding in 
the *opposite* direction creates no net magnetic field because the 
flux cancels.  This is the case, for example, if two windings are 
used as a CT primary for a push-pull amplifier with Vcc applied to 
the CT.  "No net field" presupposes perfect matching -- in practice, 
there will be some residual imbalance.)

Best regards,


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