Rotating Magnetic Field's and Inductors.

[TinselKoala]

Webby:

TK posted a "down-up" double pulse.  So let's say that was for a north-out rotor magnet.  The zero-cross of the double-pulse is the exact TDC of the rotor magnet.   So when the south-out rotor magnet passes the sensor coil you would get an "up-down" pulse.  That gives you all the information you need to know where the rotor angle is after you correlate it with the EMF induced in the drive coil.

That's right. The zero-crossing happens at the instant that the flux in the coil changes from increasing to decreasing, as the magnet moves past the "magnetic dead center" (which may not always be the exact mechanical dead center, due to asymmetries in the magnet's actual polarization wrt its physical geometry, but will usually be "close enough for govt. work" as they say.)

The interesting thing here is that the coil + rotor is slaving to an external signal generator pulse train.  That's in contrast to what we normally see were the rotor magnets themselves or optical markings on the rotor generate the timing.  So knowing the precise sync mechanism would be interesting because it's a thing that you don't see every day.

My trace was produced by a magnet moving past a -non-energized- coil, in fact the coil was not connected to anything except the scope probe. Everything you see in the trace is the result of induction according to Faraday's Law correlated with the motion of the magnet, first approaching, then receding from the coil. Examining what happens to the sign of the product (E) when the signs of the various components of the right side of the equation change, tells you what to expect from the scope trace, and experiment confirms the predictions from the formula. As you can see.

The video I posted earlier demonstrating the little circuit that detects changing magnetic flux also confirms this "double pulse" or rather, flipping of the sign of the induced voltage, since the circuit only responds to one polarity of the pulse. With one pole of the magnet facing, the circuit responds when the magnet is moving away, and with the other pole facing, the circuit responds when the magnet is approaching.

The real way to do it would be to use your DSO and then roll up your shirtsleeves, get some graph paper and a pencil, and construct a real timing diagram, or do the computer equivalent with some kind of graphical program and load in DSO captures, etc.

MileHigh

That's right.

[TinselKoala]

Here's another scope trace of what happens when a magnet is swung past a non-energized coil. Would anyone care to guess what kind of magnet I used here?

[TinselKoala]

A donut shaped one?

Bingo. Move to the head of the class !!

[gotoluc]

Would anyone care to guess what kind of magnet I used here?
Can anyone make a magnet like this?

[gotoluc]

Did you rotate the pole 90 degrees

You've been following my research but this one is not made from a magnet turned 90 degrees.
Care to try again or let others have a shot at it?

Luc