Attention Tom Permeability Of Ferrite Rods Vs Ground Balance????

Hi,, Hey Tom or anyone else that may know the answer to these questions please feel free to reply...I have read that some metal detector companies use a ferrite rod to set their ground balance on their metal detectors....Well in theory I know it would work but I'm wondering where do they get the rods? Is it the permeability of the rods that determine where it's going to ground balance at? I have worked in the electronics field for eons and have a ton of ferrite rods laying around....I have flat ones round ones big & small ones and no matter which one I choose they all ground balance out the same on a digital readout metal detector...I need some way to change a ferrite rod or whatever to a ground balance number that I choose,, like let's say a 72 or 85 etc.. Does anyone got any experience in this field or have you ever experimented on this subject? Any suggestions? What am I missing here??....Thanks....JJ

I think that is the idea - they are all the same, all equivalent to neutral ground. While it is true that at higher frequencies (100KHz to 1 GHz plus) some will get 'lossy', they all seem much the same at 10KHz.
If you are deliberately trying to make some 'calibration-standard fake dirt' you would need to start looking at powdered iron materials like carbonyl iron, etc, possibly 'blended' with ferrites.



Edited 2 time(s). Last edit at 03/05/2012 04:27PM by Pimento.

If it is pure ferrite then it is completely non-conductive and will have a zero phase shift, shape shouldn't matter. Some people have used the ferrite cores from AM radios.

Yes, the sample of standardized calibration 'test-standard'.......... is a ferrite disc in the shape of a washer.

You have probably noticed that you have to be careful with positioning of the ferrite sample, if it is too close to the transmit or receive coils, it can unbalance the coils' null. I would suggest using a number of smaller pieces of ferrite, evenly spread over an area similar to the search-coil size.
Carbonyl-irons are used in RF circuits, particularly toroidal cores, and are also used in switched-mode power-supply transformers that operate at lower frequencies, eg. 20 - 50KHz. These are usually toroids, as well. Micrometals is one manufacturer of such cores, website below. Again, small samples, spread apart, would be more likely to give results. One place you may be able to salvage a suitable core from is 60Hz power-line filters, which are obviously optimised for low-frequency operation. You could also try plain 'chemistry-lab' iron filings. Or.. perhaps just use a gallon or two of real dirt. You could 'dilute' it with sand to make it less magnetic.
[www.micrometals.com]



Edited 2 time(s). Last edit at 03/05/2012 06:20PM by Pimento.