Change of ferrite core “AL” value with frequency?

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Hello,
On page 51 of the following (below) document concerning the ETD ferrite cores, the table in blue shows two values of the “AL” parameter. (“AL” corresponds to the ‘allowance’ of the ferrite core material).
One value appears to suggest that AL is 4000 when measured at 1KHz, and the other figure for AL is 5760, and suggets that this corresponds to 100KHz.

There is also a graph on page 51 which allows one to calculate the AL value corresponding to a particular core gap size. –however, this graph is quoted for measurement at 1KHz. –What is the point in having a graph for operation at 1KHz?……hardly anybody ever operates ferrite cores at anywhere near as low as 1KHz.

Also, does the AL value really vary that much with frequency?

E series document from TDK:
https://product.tdk.com/en/catalog/datasheets/ferrite_mz_sw_e_en.pdf

 

[ronsimpson]

Inductance meter measure at some frequency.
High end meters can be set to some frequency.
I have a meter that I can set for 1k, 10k, 100k, 1meg.
I would set the meter to something near what matches the application.
I think it is common for meters to run at 1khz.
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I can't see what you are looking but:
I can see where one measurement is made at 1khz at 0.5mA while the other is measured at 100khz and 200mT and the results are (in one case +/-25% while in the other case it is minimum). APPLES and ORANGES

 

[rumpfy]

Data books dont answer all of everybody's questions. With ferrite materials, the range of use exceeds the imagination. A 1 khz test frequency allows one to compare low frequency low level material characteristics. Data is usually supplied for operation at higher frequencies as well. Also, some ferrites are used for low level analog type applications and others are used at much higher flux densities and very high delta flux change.
Some ferrites are used as high frequency low level transformers for say radio receivers. Other ferrites are used as cores in say sine wave oscillators for magnetic recording. Others are used for switch mode power supplies.
Philips invented ferroxcube materials and they own the name "ferroxcube", and they have an excellent set of data sheets for their materials. For each application there seems to be a bewildering array of suitable materials. I recently found the latest publication. It is <FXC_HB2013(philips).pdf>
The file is 10 Mb long and consists of 1200 pages of the best information about ferrites you will ever need. Good luck with the read.

 

[Flyback]

Thanks,
The most major use of ferrites today is SMPS. I mean, everything needs a power supply. I am surprised that vendors don't supply a list of ferrite core gap sizes and corresponding AL values for SMPS type frequencies.
I can work out an AL value for a given gap size using the reluctance method, (l/uo.ur.A for core and gap, then add them, then L = N^2/reluctance), however, there is an error in this, and 3D math is needed to correct it.