The applied signals are equal and opposite (assuming the turns are close together relative to the distance the field is measured at), so the sum is zero.
What are you looking to do?
Tim
-- Seven Transistor Labs Electrical Engineering Consultation Website:
if by center you mean the start of the winding you'll get the same field as from a single winding, only twice as strong.
the coil would get hotter. and a non-alternating magnetic field would be produced.
-- umop apisdn
Yes, you are wrong.
I think a DC offset would provide a fixed field the alternating field would be superimposed on.
In this case the magnetic fields will only add. This can not give a new frequency. You may be thinking of multiplying the fields. For example, if you had an alternator where the rotor was turning at frequency X and you varied the field coil at frequency Y you would end up with frequency X+Y in your output.
-- Rick
You might get a better response by posting this to the group sci.electronics.design-by-magic :-)
-- Regards, Adrian Jansen adrianjansen at internode dot on dot net Note reply address is invalid, convert address above to machine form.
You have it backwards, I think. He's driving the OUTSIDE of one coil with the + signal, and the INSIDE of the other coil with the - signal, so the currents in the two coils will be (more or less) the same.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
I believe that Tim is mistaken. Well, in this case I _know_ that _some_ Tim is mistaken, because I believe that Tim Williams is mistaken. In fact, I can be certain that some Tim _W._ is mistaken. See my other post, but I believe the effects will add, not subtract.
In that case then you want to drive both the inside and the outside with the same signal.
Your language is confused. If we forget, for the moment, the wacky coil arrangement and just consider a single flat coil (i.e., twist the wires together in the center, and drive your zip wire with your +signal and your
-signal), then the polarity of the field will, indeed, reverse at 200Hz -- this is just a really confusing and indirect consequence of feeding 100Hz AC to the coil.
The much more direct and easy to understand consequence is that you'll have a magnetic field that follows a 100Hz sine wave (assuming you're shoving a sine wave into the thing).
That's hard to tell...
If one or both of your signals are DC offset, then the magnetic field will have a DC component to it.
Clearly you're trying to do _something_. Perhaps if you pull back a bit from the bark and tell us about the tree you're pursuing, if not the whole forest.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
It would make the coil more attractive. At least to anyone made of iron.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Oops, yeah.
I had a 50% of being right, and sometimes, that happens. :^)
Tim
-- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
The idea was to have one winding of the coil fed CW and the other CCW so their fields would oppose. IOW one is N when the other is S.
But by putting one signal 180 degrees out of phase, I believed the field polarity would alternate.
For example, if the frequency was 100Hz, the rate of alternation would be twice this. As one winding is energised,the other falls off, and vice versa.
Please correct me if I am wrong.
Then I was wondering how this would be affected if one of the signals had a DC offset.
Mark Granger
Excuse me if I posted this before. I was having trouble with my news server. It did not appear in my news reader or Google groups, so I am trying again.
Behavior of Spiral Coils
I would like to wind a flat spiral coil out of thin zip wire. This will give me two separate windings side-by-side.
One signal, any audio frequency, will be fed into one winding at its outer end. The other signal will be fed from the center of the second winding. The remaining ends are grounded via a common load resistor.
The signals are the identical, except that one is 180 degrees phase shifted (anti-phase). According to my understanding, this will produce a magnetic field that reverses polarity at twice the frequency of the applied signal.
I am then wondering what change would happen between the windings if one of the two signals was given a DC offset.
Can anyone please comment on this, or otherwise advise on the arrangement described above?
Mark Granger
in air, magnetic fields are linear, which means superposition applies. Which means you can solve the problem for one source, then solve the problem for another source, then ADD the two together. Your description discombobulated my brain [doesn't take much] but remember you will NOT get any new frequency fromanything you do like you described. And fields are a vector addition.
If you want a 'circularly' polarized field, take two equal coils and mount them concentrically in quadrature, Envision a world globe with a Greenwich meridian coil and an equator coil. Now drive each coil not in 180 phase but 0 phase and 90 phase THEN you will get a circularly polarized magnetic field extending out from your coil systeem. It will act EXACTLY like hanging a permanent magnet and spinning it at the frequency of choice.
Given the bifilar winding, my thinking was that while the current in the CW winding is increasing, the current in the CCW winding (driven by the antiphase signal) would decrease. That would mean one polarity would dominate.
When the situation is reversed, the other polarity would dominate.
Both signals swing positive relative to ground BTW.
This seems logical to me. Maybe I didn't explain it well enough.
I am not sure what you mean by + and - signal. Both have the same swing, one is just inverted.
In the configuration I described above, it would seem that the added DC offset would result in current opposition that would inhibit the emitted field.
This is really just an experiment to help me understand spiral coils. You can do those sort of strange things once you retire.
Mark Granger
Having read some of the other responses I am left wondering if you were looking at a Magnetic Amplifier or even a Magnetic Modulator . It would be clearer if you were to identify your aims.
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You need to learn more about physics and electromagnetics.
1) a flat spiral coil out of thin zip wire is going to be troublesome to implement if the wire pair plane is flat on the winding plane: -- oo --- oo ----- (looking into the wiring plane and seeing 2 turns). The reason is that the inner-most wire of the pair is gong to be compressed, and the outermost wire is going to be stretched. Simple physics. 2) Your understanding concerning the magnetic field is totally incorrect. Visualize the magnetic field of just one winding all by itself. Then do so for just the other winding. Use the simple physics and electromagnetic principle of superposition OR just add them at every place. Note they more-or-less cancel. AC, DC, one on the other, whatever. Same principle. Go back to the textbooks.
Why don't you simulate this in any program such as LTspice? I think you have some fundamental misconceptions.
and add them. See what the sum produces.
I'll point out the simple statement that addition of sine waves of the same frequency always produce another simple sine wave of the same frequency with the amplitude possibly being zero. Look up linearity. There should be nothing non-linear about your coils.
-- Rick
I must be thick, but I don't see how they can cancel at the point when one signal is at maximum voltage and the second (anti-phase) is at zero.
The second has effectively sends no current through its respective winding.
And additionally, at any given time the current in the two windings is unequal, so cancellation would not be complete.
Did you read my OP?
Mark Granger
The situation you describe here is phase quadrature. sin(wt) & cos(wt). They don't cancel and you get a field of sqrt(2)sin(wt+pi/4)
*Antiphase* means exactly that the voltages are Vsin(wt) and -Vsin(wt)The fields would then almost exactly cancel out or double depending on how the two coils were wired together.
You can work out the resulting linear super position of two (or more) magnetic fields of the same frequency (or different frequencies for that matter) from the mathematical identity:
sin(A) + sin(B) = 2sin((A+B)/2)cos((A-B)/2)
Yes. You make very little sense.
-- Regards, Martin Brown
incorrect.
place.
You need to look at the values of a sine function as the input value increases over a few dozen radians. Zero is not where you thought.
?-)
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