Anyone familiar with SMD ferrite beads. I measured one with a capacitor reader and it came up as .3 ohms. Is that a valid value or it there an equivalent. 120OHM etc…
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no help, but to thank you for asking.
I’ve wondered how to tell if ferrite beads are doing their job. I mean, they just sit there, right, fluxing away. No idea how to measure if they’re doing it right, other than see if the SNR is “better”, right?
They are just little coils of wire… inductors. They will read as very low resistance and are read in microhenries.
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That’s a very strange way to sell/measure them.
They are normally sold in measurements like .56uh
They normally aren’t critical in values unless they are in some kind of RF circuit. They are often used on arcade game boards as small power filters and fuses.
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Inductors have ac resistance (impedance) and a standard multimeter will not help. Further this impedance value is for a specific frequency, and will have different values.
Your best bet is to use the new LCR meter to obtain the inductance of the bead.
You can then calculate its reactance at the frequency you want to filter out. This value will help estimate the filtering and/or cleaning up noise.
http://www.electronics-tutorials.ws/accircuits/ac-inductance.html
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For ferrite beads, the impedance specified in the datasheet in ohms is for a given frequency, usually 100MHz. The frequency is specified in the datasheet, but also there should be a graph that shows the impedance over a frequency range which is probably more useful. Here’s a typical datasheet for example:
I’d think an ESR meter could give a useful reading but only in the case that it uses a frequency which is of interest to you. One of the meters we have uses 100KHz and the other is probably similar. At least for the ferrite bead I linked, and apparently the one you measured, the inductive property isn’t much relevant at that frequency and so the impedance is simply the dc parasitic resistance which is nearly zero.
Another way to measure one (and to get a graph of impedance over frequency) would be with a network analyzer or a spectrum analyzer, which we don’t have just yet, but with only a little more effort you can obtain similar results with an oscilloscope and function generator which we do have. Our frequency generators probably top out at 20MHz which again may or may not include your frequencies of interest.
Graphing the response yourself is particularly interesting because you can use the same equipment and a similar procedure to characterize the effect of the ferrite bead in your actual circuit and see what it’s really doing or not doing.
The following article is a good introduction and overview of ferrite beads, even if you don’t read it to the end. As with anything, you can go as far down the rabbit hole as you like.
http://www.analog.com/en/analog-dialogue/articles/ferrite-beads-demystified.html
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Our newest LCR meter will perform its measurements at 100Hz, 120Hz, 1KHz, 10KHz, and 100KHz. Just an FYI
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There is an assortment of SMD ferrite beads and SMD capacitors in the Electronics Lab. Look at the first metal shelf on the right as you walk into the Lab, probably the second shelf from the top. Then look for some small blue plastic binders. These components are all properly marked with the vendors part numbers. Check the vendors website and it will give you the parameters. Good luck.
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