Simplest Way to Measure Bs, Br and Hc of an Unknown Iron Core?

[TimFox]

The method was tedious, involving manual reversal of the coil current and noting the maximum excursion of the galvanometer.
The next student to do the lab experiment used a rudimentary analog computer to do the integration.

[KerimF]

I am surprised that no one liked to ask me about the known basic formulas from which the 3 formulas on post #10 were derived and let the measurement be simple (relative to the conventional known methods).

Perhaps no one here is ready to believe they are valid because they are not known or approved by any scientific site.

The irony is that a new idea, by definition, starts always from one person in the world, unless a few individuals may think of it in the same period of time, in different regions on earth.

[Conrad Hoffman]

I have never seen one of these in the wild, and the photo of the head isn't very good, but the manual may offer some useful information:
https://www.ietlabs.com/pdf/Manuals/GR/1670-A%20magnetic%20test%20set.pdf

The patents can also be looked up but I don't know if they offer more info.

[TimFox]

Note the wide range of units discussed in the "Introduction" of the G-R manual.
Present-day SI units for magnetic variables are listed there as "MKS, rationalized (MKS-R)".
Rationalized vs. non-rationalized involves a factor of 4 pi, besides the orders of magnitude from cm vs m, etc.

[KerimF]

I have never seen one of these in the wild, and the photo of the head isn't very good, but the manual may offer some useful information:
https://www.ietlabs.com/pdf/Manuals/GR/1670-A%20magnetic%20test%20set.pdf

The patents can also be looked up but I don't know if they offer more info.

Sorry, I am not sure what I am supposed to learn from reading this PDF. Does it explain a simpler method than the one I use?

[Conrad Hoffman]

GR was very good at explaining the fundamentals underlying the designs of their equipment. They were usually rigorous in accounting for subtle errors. I've found I always learn something from them though many people are smarter than me and don't need more information.

[KerimF]

Note the wide range of units discussed in the "Introduction" of the G-R manual.
Present-day SI units for magnetic variables are listed there as "MKS, rationalized (MKS-R)".
Rationalized vs. non-rationalized involves a factor of 4 pi, besides the orders of magnitude from cm vs m, etc.

The units I am familiar to are of MKS, Tesla (for Bs and Br), A/m (for Hc), Weber (for ‘Φ’, the Magnetic flux) and H/m (for μ0=4*pi*1e-7).

[TimFox]

Those are SI, and our voltmeter calibrations agree with it.
However, there are many more sets of units that have been or are in use in physics and engineering, even English units (line/in², etc.) and one should be aware that they exist.

[KerimF]

GR was very good at explaining the fundamentals underlying the designs of their equipment. They were usually rigorous in accounting for subtle errors. I've found I always learn something from them though many people are smarter than me and don't need more information.

The needs of an adult determine his professional knowledge in life. The different needs of humans let their knowledge complement each other.
In other words, the lack of knowledge about something is simply the lack of interest about it, for one reason or another, no matter if the person, in question, is genius or not.

In my case, I like to learn (or discover) what I can apply in real and be useful to me in a way. But I may like to hear some other things just to pass my free time or for fun.

[johansen]

I have found that cheap microwave oven transformers start to saturate at 1.2T but they run them at 1.7 to 1.9.

They are gain oriented, allegedly. The I piece comes from two E pieces.

As such most of the core is oriented correctly but the short segments are not, hence the soft saturation.


Anyhow just wind a coil and measure the power consumption after subtracting copper losses

[KerimF]

Those are SI, and our voltmeter calibrations agree with it.
However, there are many more sets of units that have been or are in use in physics and engineering, even English units (line/in², etc.) and one should be aware that they exist.

I work with the MKS units, but I am also aware of all sorts of other units since, once a while, I need to convert them to MKS ones while solving new equations and getting new formulas at work.

[TimFox]

@KerimF
Another common unit for magnetic flux density B is the Gauss.
1 Tesla = 10⁴ Gauss.
However, Gauss is a unit in non-rationalized cgs, so the corresponding unit of magnetic field H is the Oersted, but in vacuum B = H, different from in rationalized units.
You will find Gauss used often, since the Tesla is rather large and the Earth's field is very roughly a Gauss.
Tabulations of magnetic materials often use Gauss and Oersted, so you should understand them as well as Tesla and A/m².

[KerimF]

I have found that cheap microwave oven transformers start to saturate at 1.2T but they run them at 1.7 to 1.9.

They are gain oriented, allegedly. The I piece comes from two E pieces.

As such most of the core is oriented correctly but the short segments are not, hence the soft saturation.


Anyhow just wind a coil and measure the power consumption after subtracting copper losses

Good remark, thank you.
I will try to test a coil whose core is made by the E pieces only and see the difference. Obviously, its new structure will not be practical at all. It will just help verifying your remark.

And the power consumption (real power) can be measured rather easily by a scope having the Ch1*Ch2 function (which I have).

[KerimF]

@KerimF
Another common unit for magnetic flux density B is the Gauss.
1 Tesla = 10⁴ Gauss.
However, Gauss is a unit in non-rationalized cgs, so the corresponding unit of magnetic field H is the Oersted, but in vacuum B = H, different from in rationalized units.
You will find Gauss used often, since the Tesla is rather large and the Earth's field is very roughly a Gauss.
Tabulations of magnetic materials often use Gauss and Oersted, so you should understand them as well as Tesla and A/m².

I am sorry for giving you the impression that I don't understand well all the other units you mentioned.
You are right that most tabulations of magnetic materials are given in Gauss and Oersted. And I used to convert them to Tesla and A/m

If I am not wrong, you give me the impression that I have to make another version of my 3 formulas and let it be suitable for Gauss and Oersted (what about the length unit?).

[TimFox]

Technically, Gauss should be used with cm.
Note that Gauss and Oersted form a non-rationalized system, so the equations are different from the rationalized system such as rationalized MKS (SI) using meters, where there is a dimensional difference between B and H.

[KerimF]

Technically, Gauss should be used with cm.
Note that Gauss and Oersted form a non-rationalized system, so the equations are different from the rationalized system such as rationalized MKS (SI) using meters, where there is a dimensional difference between B and H.

To check if the new 3 versions are right, their results, for the same coil, should be:
New Bs, Br (Gauss) = 10000*old Bs, Br (Tesla)
New Hc (Oersted) = 4*pi*1e-3 * old Hc (A/m)

[KerimF]

The 3 formulas of Hc, Br and Bs on post #10 are for the MKS units (A/m, Tesla and m).

The following 3 formulas are for the non-rationalized cgs units (Oersted, Gauss and cm):

HHc [Oersted]= Khh * I_Bzero
where
Khh = 4*pi*N/LLm/10
LLm, in cm

BBr [Gauss] = Kbb * V_max * cos(wt_zero) / w
where
Kbb = 1e8/N/AA
wt_zero = arcsin(V_Izero / V_max)
w = 2*pi*F
AA in cm2

BBs [Gauss] = (Mhh - HHc) / (Mhh / Mbb - HHc / BBr)
where
Mhh = Khh*I_max + HHc
Mbb = Kbb*V_max/w - Khh*I_max

[KerimF]

To complete the topic of this thread professionally, I will answer the question that no one asked me:
What is the well-known work on which your 3 formulas were based and derived?

Its answer is simple to those who are familiar with LTspice simulator.
They are derived from the work of John Chan in modeling a non-linear coil.   

To those who don’t have LTspice, I attached a PDF of the LTspice help page which is related to John Chan model.
His two formulas, one for the positive BH branch and the other for the negative one, are the Bup(H) and Bdn(H) respectively.

Obviously, if someone will be able to prove that any of my 3 formulas is not valid, he simply proves me that John Chan model is also not valid.

Regards,
Kerim