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Just What Is Iron Bias??


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While this topic is hot and on our minds, I'm going to make a request.  Could someone with detailed technical & engineering knowledge write up a report explaining Iron Bias at an intermediate-to-advanced user but still layman's level?  The kind of description I'm requesting is one similar to what was done in Randy Horton's excellent monograph Understanding Your X-TERRA which contains an interview with Minelab scientist&engineer Dr. Laurence Stamatescu (starting on page 79) where he melds the right combination of technical info and easy to follow wording.

Maybe there has already been such a writeup that I'm not aware of, but although I appreciate what has been posted here on the forum on this subject I'm still confused/confounded as to what is going on and how to best utilize it.  I don't seem to be alone on that.  One of my many gaps in understanding is whether or not all detectors have an effective (but fixed) iron bias setting, with only a few giving the user the option of dialing it in for best performance.  Related: when iron bias on the MInelab Equinox is set to zero (in either F2 or FE), is there still some kind of iron bias occurring?  Knowing how a detector works transfers over to optimizing it's use and I'd like to do more of that instead of just locking iron bias on one value for all applications and conditions (or blindly accepting factory defaults) -- what I (and apparently most users) do now based upon ignorance.  (Well, I'm ignorant on this subject -- not trying to associate that with any of you.  😏)

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Hopefully somebody at Minelab takes note and puts out a paper. I honestly do not delve much into deep technical details these days, as the answer is inevitably proprietary. And I'd possibly not understand it anyway. :smile: I just need to know what a control does, and running it to extremes and a few simple tests reveals a lot. For me it is a filter that literally shifts the bias on where the detector draws the line between ferrous and non-ferrous responses. All detectors draw this line, but most can’t be adjusted at the guts level, but by manipulating the ferrous break point via target id. This is deeper than that, but still, it has to exist in all detectors at some level. Otherwise you are describing an all metal circuit, no differentiation between ferrous and non-ferrous.

FT users do not like digging ferrous, so their machines have an extra bias against ferrous, and therefore will call more non-ferrous items incorrectly. NokMak uses this to advantage, by revealing non-ferrous items FT detectors generally miss at presets. Most U.S. detectors are like this, and you have to accept negative numbers to capture the missed non-ferrous. Rather than shift the numbers, iron bias shifts the underlying filter. Lower numbers allow more ferrous through, but also more non-ferrous, higher numbers suppress the ferrous, but at the risk of losing ferrous. It’s a trade.

More on Iron Bias, with video

https://www.detectorprospector.com/forums/topic/1378-european-detectors-versus-us-style-detectors-on-target-masking/

9FC11310-F876-48C7-91FE-079AF7FC1E06.jpeg

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That was my understanding too, that instead of shifting all the I.D. numbers to a new "normal", you just shift the underlying dividing point between ferrous and non-ferrous. Kind of reminds me of the old school yard dare, where you draw a line in the dirt and challenge someone to cross it. If they back down and not cross, you drew it in the right spot. If they step over the line, you back up and draw another line and then dare them to cross that one. If they do, it's either a third line or a fight!

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In many detectors you will hear this called 'bottle cap' reject.    If your detector has a bottle cap reject filter you have a FE bias setting available to you.  If you have both bottle cap reject and a hot rock filter you basically have a dual FE bias/FE mineral  filter that you can tweak for iron bias at both ends of the 180 degree spectrum.

Tom Dankowski thinks the normal FE Bias filter on the Equinox 800 was too high and didn't let him go low enough into the iron...so he worked with Minelab for the FE2 setting.   He polled the FE / FE2 user settings people were using all last fall.

HH
Mike 

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I don't guess you can blame the guy.   Even though its a lot of work it is nice to be affiliated with a detector and say you helped develop it and bring it to market.  I know I've gotten to say, 'we' a few times myself. 

My one big wish for Tom was that he lived somewhere where there was dirt.  

HH

Mike

 

 

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I don't blame him at all. I've been doing it for over twenty years. :smile: I'm especially proud of the little bits of me in TDI and Equinox. I did product reports on F75 and many others, but prefer the projects where I had or have engineering input. Can't be calling the kettle black! :laugh:

Yeah, the low mineral tests are useless for me. Tom is a brilliant man, and we have always got along great. Some of his articles are genuine classics. But I have to chuckle when he drops into his unique version of "geek speak"

 

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