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solenoid synchro?

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Eric HertzEric Hertz 04/26/2018 at 20:270 Comments

Still trying to figure out what would happen with the AC-driven unipolar stepper arrangement of the last log... came up with this plausible solenoid-synchro using permanent magnets:

If this works as I imagine, it's very different from merely connecting the two solenoids in parallel, and not connecting an external power source. 

In That case, an external force moving the 'sensor' solenoid's magnet only induces a current when the magnet is moved. When stationary, no current flows, thus, it's entirely possible to have the two magnets in entirely different starting positions. 

Also, the current induced by a small/slow movement would be far too weak to overcome external forces like friction and inertia.

With the AC-driven arrangement, the frequency must be much higher than can actually cause motion... But, if it works as I imagine, the effect of a stationary permanent magnet on a single winding should be a net DC bias. 

Connecting two windings in parallel, then, would tend to cause both magnets to position themselves similarly so the DC bias on each path matches.

This, then, would synchronise the two magnets even if they have differing starting-positions.

Lots of weird effects to consider: eddy currents, ferrous vs air-core, saturation... Then some other interesting ponderances: A larger AC voltage would give a larger DC offset... intriguing. And what if the two coils were in series, instead? (More like the stepper-scenario of the last post... and more like the synchro diagram from Al W.... and making me ponder Y vs Delta configurations for synchros).

Surely not at all efficient, but something, anyhow.

Some reading material with basically the conclusion that it depends heavily on the characteristics of the solenoid and magnets:

https://electronics.stackexchange.com/questions/276988/what-effect-does-permanent-magnet-have-on-an-air-core-coil

https://electronics.stackexchange.com/questions/242082/how-does-inductance-change-with-presence-of-different-directional-magnetic-field

https://www.quora.com/How-does-inductance-change-with-presence-of-a-directional-magnetic-field

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