# Not sure about Manufacturers response

• posted

I ask Laird EMI Products a question about a graph of Z regarding their Ferrite beads made to choke coax. Each bead has between 9 and 62 ohms Z. (depends on geometry) Here's the graph on page 3.>

I ask if they have a graph that separates the R and XL. Thinking Z is a phasor of XL and R.

They responded;

I?m not sure any of this applies. Ferrite cores have no inductance, and the ?resistance? is the ?impedance? (Z value). Really all there is for these parts is the Z value impedance.

Does anyone think the Z is all R and no XL?

Mikek

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Obviously, a sales person who has no formal (or even informal) training in electrical engineering.

Jon

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Kramers?Kronig relation gives R and X from a plot of Z.

Tim

```--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design ```
• posted

I suspect this is a math thing and I don't understand it. I see no way to take a graph of Z and get R and XL from it without more info. If you could explain further it would be helpful. Mikek

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I don't have a program to implement it, but you will find it happens naturally when you build a model that fits the Z curve. Give it a try in Excel or MATLAB/Octave, or just here,

(use an overlay program to get the curve-to-be-fit to show on the graph).

Tim

```--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design ```
• posted

Example:

Enter those values and compare the graph with the datasheet. Try setting the Trace plot type to Real or Imaginary, instead of Magnitude.

Tim

```--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design ```
• posted

Well, if you are poking a short length of wire through a bead, the R is going to be really small. With a coax passed through, the R of the center conductor is going to be a little different from the shield, but both should still be fairly small (fraction of an Ohm for a few inches). So, it is all Xl, which is likely to be tens to hundreds of Ohms for small, one-turn toroids.

Jon

• posted

Which R?

DCR is not the parameter of interest, relating to ferrite beads. ;)

Take a look at the equivalent circuit I gave in another response.

Tim

```--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design ```
• posted

If you note, Z does not go up by 10x when f goes up 10x. It's lossy. If you put it on an LCR meter, it registers resistance more than inductance.

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Thanks,
- Win```
• posted

On Nov 20, 2017, Winfield Hill wrote (in article ):

I haven?t been following this thread, but have a comment/observation: Many handheld LCR meters are wildly inaccurate on low-Q inductors because they measure the magnitude of the impedance and assume that it?s all due to reactance.

Joe Gwinn

• posted

Of course, and this is the whole reason for the OP's question. The R is the R of the user-supplied conductor(s) the user puts through the ferrite item, and is going to be quite small. So, all that matters is the XL, which they give in their charts. The ferrite doesn't alter the R at all, all it adds is XL.

Jon

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Yes, despite Q, I am sure on a good impedance bridge, you would see some inductance, but R close to zero with these items.

Jon

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• posted

Not at all. The ferrite is lossy so it adds significant R (at high frequency). There is a reason that ferrite beads are rated in ohms.

• posted

^^^

And it's not just that it's |impedance| at 100MHz, but it's largely resistive around that frequency.

But how can you get from ~0 ohms to ~100 ohms, over some frequency range? By taking on inductive reactance. Rising impedance --> inductance; falling impedance --> capacitance. This is the Kramers-Kronig relation.

You CANNOT have a one-port, that is real, causal, and has nonminimum phase, or a frequency-dependent _resistance_ (all real). Rest assured any place you see something that's implied to be otherwise, it's a lie, and a poor one at that. :)

Tim

```--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design ```
• posted

I would expect that to be frequency dependent as well as drive dependent. These ferrites are designed to be lossy, but i would expect less loss if the drive is below some specified level (and so one should see an Xl at least as much as an air-core version).

And one should expect good operation in some specified frequency range; perhaps a capacitive term above its (specified) frequency range.

• posted

HOW in the #\$(W!#& heck did the text become grey and thus less readable?

• posted

I think they mean the shunt resistance of the ferrite.

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This email has not been checked by half-arsed antivirus software```
• posted

This is not my area of expertise, but won't skin effect have a large influence in the MHz range with a solid wire through a ferrite bead? There is a note on page 4:

" All impedance values for high frequency cores are NET ; NET impedance is impedance of the ferrite core only All impedance contribution from the test wire and fixtures has been removed. "

That would indicate that they measured the impedance of the wire without the ferrite bead at various test frequencies, and did a vector subtraction from that measured with the bead.

Paul

• posted

Probably your newsreader has interpreted everything after the "--" as a .sig.

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