B-H measurement 1

[Sgalb]

Would someone please enlighten me on how a B-H curve is generated for an unknown material? Also, for the relative permeability number that one sometimes finds published. Thank you.

 

[EdStainless]

The general method involves placing the sample into a magnetic circuit with a probe or coil to measure the field levels. Then energize the coils in the circuit and saturate the sample, then reverse field and drive it through the second quadrant. The measured applied (external field) is the H and the field in the sample is the B.

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Plymouth Tube

 

[MagMike]

Sgalb: Regarding your question about relative permeability,
this is the permeability of free space. Its value depends on which unit system you are using.
In cgs units, relative permeability is 1.0
In SI units, relative permeability is 12.57e-7 Henries per meter

Is is possible you meant recoil permeability? This is different and refers to the slope of the straight line portion of the normal (not intrinsic) BH curve in the 2nd quadrant. This one is only used with permanent magnets.

Mike

 

[Sgalb]

EdStainless: Thank you. Can I generate a B-H curve using experimental apparatus or does it need to be done to some standard on standardized equipment? I have an LCR meter, several coils, and a gauss meter.

MagMike: I guess I'm still comming up to speed in this area of physics. Maybe I meant absolute permeability. I'm doing some eddy current work and understand that conductors such as copper and aluminum have permeabilities the same as free space, thus the relative permability become 1 for a skin depth calculation. On the other hand, ferro and ferri magnetic materials have permeabilities greater than 1 and they also increase the inductive reactance load Xl on a sensor coil because they concentrate field H and increase flux density B. Comment?

 

[MagMike]

Sgalb: You'll also need a bipolar power supply to energize the coils positive & negative. I'd suggest a fluxmeter (or integrating voltmeter) to measure the field in the search coil (the one that surrounds the magnet). You'll also want to have the test material in a closed magnetic circuit.

For truly accurate measurements, I recommend sending the parts to a lab. There are a number of good ones in the US that'll charge a reasonable fee, they've been mentioned in a threads before.

Regarding permeabilities: I had a class in NDE many years ago that included eddy current testing. From what I remember of those days, your description/understanding of the permeabilities in aluminum, copper, ferri- and ferromagnetic materials is correct. I think we called it maximum permeablitiy back then. I don't recall the term absolute permeability, but things may have changed.

Mike

 

[Sgalb]

Thank you Mike and Ed, regards.

 

[EdStainless]

Send it out for testing. It is interesting, but not worth the effort.

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Plymouth Tube

 

[Sgalb]

Ed,

Thanks. Would you have a couple of company names of the top of your tonge in the U.S. I could look up? A few of the key words I tried on Google and this forum didn't connect with any solid hits.

I doing a research experiment and am not sure if I can characterize a sensor response and call that evidence or if I need to quantify the properties accurately so I'd like to get a quote.

 

[MagMike]

Here are two places in the US that can measure the BH loop for you:

KJS Division of Magnetic Instrumentation:

http://www.kjsmagnetics.com/test.htm

MagnetPhysik:

http://www.magnet-physics.com/

Sample geometry is important. I'd recommend calling them up to find out what shape/dimensions would work.

Mike

 

[Sgalb]

MagMike,

Most appreaciated,

Regards

 

[Bronzeado]

Hi folks,

Regarding large power transformers (above 100MVA) how the B-H (saturation) curve is obtained?

Best regards,

H. Bronzeado

 

[EdStainless]

You should start another thread Bronzeado.
But since we are here I'll comment.

They build a sample stack of laminations around test coils. Then they drive one coil with signal generator (known EMF) and the other coil is used to measure.
On big units this is done on small pieces cut from the actual laminations.


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Plymouth Tube

 

[Bronzeado]

EdStainless,

Thank you for the advise.
I will start a new thread.

All the best,

Herivelto Bronzeado