[time-nuts] NIST isolation amplifiers
kb8tq at n1k.org
Wed Nov 26 22:11:10 EST 2014
If you look at some of the wire that they use, the rating may be as much a wire rating as a core rating. They use *small* wire !!!
I’ve always assumed that if you go over 30 ma anywhere on any winding you are in trouble. I suspect that DC through the entire winding (ignoring the center tap) is a “legal” thing to do.
> On Nov 26, 2014, at 6:39 PM, Charles Steinmetz <csteinmetz at yandex.com> wrote:
> 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.)
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