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Determining y intercept of BH loop

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BobM3

Mechanical
Mar 27, 2005
670
Given an BH curve for a material, like low carbon steel, is it possible to predict how far into saturation you would need to go to produce a particular amount of residual flux density?
 
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If the part was saturated, by default the Y intercept will be the remanence of the material. It'll follow what is sometimes called the major hysteresis loop.

If you want something lower than the remanence, then things get a bit trickier. You need to know the permeability & magnetic history of the steel.

Can you give a bit more explanation of what you are looking for?
 
I'm investigating different ways to sense speed in a high speed motor. One way would be to use a hall effect device and a magnetized "toothed" wheel. For prototyping I'd like to build something cheap and fast. I know how much B I need to trip the sensor. I need to come up with the material and how much amp turns I need to magnitize it.
 
Are you trying to magnetize just one "tooth" or all of them (in an alternating N-S pattern)?

Depending on the geometry of the "toothed" wheel, you might be able to sufficiently magnetize the part by (carefully) pressing a rare-earth magnet onto the tooth.
 
It's just a two toothed "gear", each tooth 180 degrees apart.

So it doesn't matter how far into saturation you go to leave you with the remanence value? You must have to go a significant amount past the "knee" though, correct?
 
Yes, it doesn't matter as long as the part is saturated. Since you are only doing a fast & simple experiment, it'll be difficult to tell if you saturated the part. You'd need some method to measure the complete hysteresis loop to tell how far beyond the "knee" you are.

The only option I can think of is to magnetize the part, measure the magnetic output, then increase the magnetizing pulse by 10% (or some other, arbitrary value) to see if you get a higher reading. Keep increasing the magnetizing pulse until you see minimal to no increases in magnetic output on the steel. At that point, you can be reasonably sure the part was saturated.
 
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