Book Excerpt : " Iron Bias "

[cjc]

Book Excerpt: "Iron Bias" 
(Settings X 6 + long press, “+” or “-“ to adjust, “Detect” to exit).
The need for an Iron Bias setting on the Equinox derives from the operating characteristic of a high gain detector. While the Equinox’s sophisticated electronics act to inhibit inconsistent responses like iron, at the same time because there is so much Sensitivity going down into the ground there is still the possibility of iron falseing taking place. This involves iron objects that have very unusual properties such as a spike nail upended, or something large enough to mimic a non-ferrous response by overwhelming the machine’s circuits and coming in at the top of the discriminate range (termed “wraparound”) While these are usually recognisable by target testing (cross sweep for one), at the same time there is a need for a control that regulates the level of consistency in a target which is assigned the audio (rougher or broken tone) of iron. This feature is also useful to relic hunters or anyone wanting to hunt for coins in dense iron. You have the choice of trying to knock the iron out by way of the Equinox’s software, or opening up the machine to get cleaner, fuller responses on iron in order to hear what’s mixed in with it. 
In effect, “Iron Bias” is a filter. Whereas the ground’s signal represents a large, unstable, response, a good target can be seen as a small, narrow and consistent response. “Iron Bias acts to mediate the “line” where this distinction is made. This doesn’t just include iron—but any object which contains multiple metals. So “Iron Bias” can be used to change responses from bottlecaps, corroded coins—anything that’s not “clean” metal such as silver, copper aluminum or gold. It’s worth noting though that with some targets that are comprised of both iron and non-ferrous metal, “Iron Bias” may act to “clean up” the signal—making it sound better. This is similar to the way that many rusted targets will sound better after several passes of a BBS detector (Sovereign / Excalibur) coil. The machine’s built-in bias is removing the inconsistent parts of the signal. Conversely, a lower setting can emphasise the alloying of an unwanted target--effectively “breaking it up.” 
It’s worth noting though that because all metal in the ground “mixes” with it’s signal (corroded or not), using high levels of “Iron Bias” acts to reduce detection of all targets. 
Understanding how “Iron Bias” works is an important lesson in how detectors work. In effect, they don’t just “punch down” though the ground to detect a metal target. Instead, what a detector does is to assess both the ground and any metal that’s in it and then separate the two—based upon this consistent / inconsistent scale. This is the scale that an “Iron Bias” control operates on. 
“Iron Bias” can also be used a tool to moderate the effects of “black sand” by changing the machine’s response to the large, scattered inconsistent response it produces and promoting any “clean” metal targets that are mixed in with it. It also has the potential to stabilize the detector in “black sand” by reducing the Sensitivity to this erratic signal. This may require a higher or lower setting depending on the conditions.
When many hunters want to get the maximum depth with the Equinox, they take the “Iron Bias” right down to “1” or “2.” With this setting it’s generally agreed that frequent “Ground Balancing” of the machine helps to reduce the response to iron. 
The “trade-off” here though is that you will still be “fooled” by more iron false signals. 
From: "The Minelab Equinox: From Beginner to Advanced" 
by Clive James Clynick

Thanks for a great forum Steve!

cjc

 

[Jackpine]

Using iron bias definitely has its plusses and minuses.

Tom

[SittingElf]

Thanks for posting this. I'm convinced...and ordered!

[cjc]

On 4/16/2018 at 6:48 AM, SittingElf said:

Thanks for posting this. I'm convinced...and ordered!

Hope you like it--Im going to send one to Steve and see what he thinks as well.

Regards,

clive

 

[GB_Amateur]

2 hours ago, cjc said:

On 4/16/2018 at 6:48 AM, SittingElf said:

Thanks for posting this. I'm convinced...and ordered!

Hope you like it--Im going to send one to Steve and see what he thinks as well.

Ordered mine yesterday.  I'll write a review for the detectorprospector.com/forum if no one beats me to it (or if I don't agree with the ones that do ).

 

[Chase Goldman]

Clive 

Good explanation of iron bias but I wish you spent a little more text addressing the potential tradeoff of utilizing iron bias as the quoted phrase below is rather vague.

On 4/15/2018 at 8:37 AM, cjc said:

It’s worth noting though that because all metal in the ground “mixes” with it’s signal (corroded or not), using high levels of “Iron Bias” acts to reduce detection of all targets

Specifically, empirical testing by Equinox users here, has shown that even low levels of iron bias tends to preclude unmasking of desirable non-ferrous targets hiding amongst thick iron.  So there is not just a depth impact to using iron bias as implied in your write-up, there is a target separation impact as well.  Your statement above does not contradict these test results but it also doesn't provide a clear caution to the reader of specific situations where applying iron bias might not be optimal.  The "no free lunch" axiom I apply to any sophisticated filter features MD manufacturers incorporate into their detectors like the "Silencer" filter setting on the Deus almost always applies.  After all, ML apparently shied away from iron bias default settings other than zero for most modes. 

Now that I am getting used to the Equinox target audio clues, I now like to run it at or near the default for a given mode, and that means I am mostly running it at 0 even under circumstances where the iron is spread out.

Appreciate your feedback as you are obviously very knowledgeable on the topic based on the book excerpts you have graciously provided for our perusal.

Thanks.

[cjc]

On 4/18/2018 at 10:38 AM, Chase Goldman said:

Clive 

Good explanation of iron bias but I wish you spent a little more text addressing the potential tradeoff of utilizing iron bias as the quoted phrase below is rather vague.

Specifically, empirical testing by Equinox users here, has shown that even low levels of iron bias tends to preclude unmasking of desirable non-ferrous targets hiding amongst thick iron.  So there is not just a depth impact to using iron bias as implied in your write-up, there is a target separation impact as well.  Your statement above does not contradict these test results but it also doesn't provide a clear caution to the reader of specific situations where applying iron bias might not be optimal.  The "no free lunch" axiom I apply to any sophisticated filter features MD manufacturers incorporate into their detectors like the "Silencer" filter setting on the Deus almost always applies.  After all, ML apparently shied away from iron bias default settings other than zero for most modes. 

Now that I am getting used to the Equinox target audio clues, I now like to run it at or near the default for a given mode, and that means I am mostly running it at 0 even under circumstances where the iron is spread out.

Appreciate your feedback as you are obviously very knowledgeable on the topic based on the book excerpts you have graciously provided for our perusal.

Thanks.

That's true, Chase it's not much of a warning especially when you compare any bias setting to something that's wide open in the iron like an Impact.  I do give a more direct warning about using the pre-set of "6" in either of the Beach modes and suggest looking for other ways to accomplish stability or in iron definition.  It's a "cheat" like Auto Sens on the CTX--no substitute for good audio recognition and target testing.  

Thanks for your feedback first I've had!  Want a comp?  Shoot over your address. 

regards

clive

[fredmason]

If an "almost idiot" may ask...If frequent ground balancing is good, why isn't auto gb as good or better?

and thanks to all that wring the guts out of these machines!

fred

[Chase Goldman]

Fred, do you mean tracking GB?  Auto GB is like a manual ground grab but without having to hit the +/- buttons while you pump or sweep.

If you meant continuous tracking, there are situations where continuous tracking does not work well, specifically when there is not enough ground mineralization to get a decent ground grab.  In that case, the GB algorithm is essentially guessing what GB should be and may give you a bad reading.  Under conditions of low mineralization it is best to attempt a single ground grab (manual or auto) or just set GB near the mode's GB default setting which is typically zero. 

Multi IQ does a pretty good job compensating for an imprecise ground phase setting, so unless ground phase is varying by more than 10 to 15 points (which typically indicates variations in ground mineraluza tion) there actually is no need to do frequent rebalancing.  Let your ears decide whether you should rebalance as ground noise, especially in All Metal mode, will tend to increase if the machine's ground phase setting is significantly out of balance with the actual ground phase. 

For situations where there is highly variable ground phase due to mineralization, black sand, or variations in beach salinity, don't be afraid to put the machine in tracking GB.  As long as there is enough mineralization or salinity variation for the machine to detect and grab onto, tracking works well with no noticeable downside.

HTH

[fredmason]

Thanks Chase;

I don't think I have been anywhere in the West that lacks mineralization...and, yes I meant continuous Ground tracking....

thank you

fred