john sullivan
New member
when the threshold stops momentarily. does it stop detecting until the threshold comes back on?
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wondering
- Thread starter john sullivan
- Start date
MNCoinhunter
Active member
Ugh...Elton...no offense, but that sentence contradicts everything I have been reading in the classroom forum for the last two months. John Sullivan, could you be a little more specific? Are you detecting wide open in All Metal or are you using some discrimination? When you say it stops momentarily, do you mean just for one second, or for longer than that?
TURNMASTER
Active member
Many say you will hear coins ring through the nulling. It can be dis concerting though for sure especially with those LOOOONNG nulls. I do not have enough hours to say conclusively.
Jeff
Jeff
john sullivan
New member
factory setting , digital smart field.maybe 2 seconds at the most
sgoss66
Well-known member
John --
I have been working to understand all of this myself. I will tell you what I believe to be true, as best as I can understand at this point...
The machine does NOT "stop" detecting. When iron (or any other target whose ferrous and conductivity values you have set your machine to discriminate out) is present under the coil, the machine responds by "nulling" the threshold. You can think of nulling as simply your machine saying "I sense a target under the coil, but you have chosen to discriminate this target, so instead of producing an audible signal -- which is what I'd otherwise be doing right now, I will simply null the threshold." When your machine sees a non-discriminated target, it will then respond audibly.
But, iron in particular is somewhat of a special case. Iron has a particularly strong influence on detectors (due, as I understand it, to its magnetic properties), and as such, iron will often "overpower" the signal from any other nearby (possibly good) target. This "overpowering" issue can happen with ANY type of metal; for instance, a pull tab four inches above, and directly on top of, a dime, may "hide" the weaker/deeper dime signal, and thus your machine will likely "see" -- mostly or even completely -- the signal from the pull tab. However, iron is particularly good at "overpowering" nearby signals. This tendency of iron in particular to "hide" or "mask" any signal from nearby targets is referred to as "iron masking."
So, when iron is under your coil, and your threshold nulls, it certainly may be difficult for your machine to see other, adjacent targets, as these targets will often give a weaker signal than the nearby iron is giving -- but still, your detector has not "shut off." It is still sending and receiving. But, as long as your coil is receiving that strong electromagnetic field associated with the iron, there are two things occuring with your detector -- 1.) the threshold will continue to "null," and 2.) it will be more difficult for the machine to see any other good targets nearby. The "nulling" is an EFFECT of iron being present (and this IRON may cause your detector to miss adjacent, good targets); however, the nulling itself is not the CAUSE of any missed targets.
Obviously, there is a point where the effects of the iron (depending upon its orientation, location, etc. relative to a separate "good" target) diminsh, to the point that your machine can again begin to "see" the signal from a nearby, good target. I believe that this is when you will hear that good target's signal "break" the null, and report to you.
The bottom line is, IRON is what makes your machine "miss" good targets, NOT the "null" itself. The null is just alerting you to the presence of iron (or, again, ANY target you have set the machine to discriminate). When nulling occurs, and it is long and sustained -- lasting for more than just a second or two, then that suggests the presence of more widespread and/or larger iron, as opposed to a one or two second null which suggests a smaller discriminated target.
As a detectorist, nulling can suggest to you that "iron masking" is possible at that point (i.e. there is a chance you are missing some good targets). According to NASA Tom Dankowski, iron masking (combined with depth limitations of detectors) likely "hides" around 80% of all "good" targets in the ground! (Please read this EXCELLENT article... http://www.dankowskidetectors.com/behindthemask.htm ) However, this is just the nature of the beast, NOT an issue that is specific to Explorers. As I understand it, the only things you can do to "fight" the masking issue and hope to find more of those "hidden" targets are A.) move your coil more slowly, to give your machine a better chance to "see" the good target; B.) switch to a smaller coil, which means there will be less iron under the coil at any one time, thus less "masking," and more ability to see the nearby "good" targets, and C.) DIG AND REMOVE THE IRON, so that obviously, the iron's ability to hide a good target has been eliminated! Obviously this is not practical when the iron is pervasive, but digging some of it may help. Meanwhile, slowing down your sweep speed, and switching to a smaller coil are options that some of the more experienced guys on the forum have recommended.
Hope this helps, and if I have made any mistakes here, someone will correct it I'm sure...
Steve
I have been working to understand all of this myself. I will tell you what I believe to be true, as best as I can understand at this point...
The machine does NOT "stop" detecting. When iron (or any other target whose ferrous and conductivity values you have set your machine to discriminate out) is present under the coil, the machine responds by "nulling" the threshold. You can think of nulling as simply your machine saying "I sense a target under the coil, but you have chosen to discriminate this target, so instead of producing an audible signal -- which is what I'd otherwise be doing right now, I will simply null the threshold." When your machine sees a non-discriminated target, it will then respond audibly.
But, iron in particular is somewhat of a special case. Iron has a particularly strong influence on detectors (due, as I understand it, to its magnetic properties), and as such, iron will often "overpower" the signal from any other nearby (possibly good) target. This "overpowering" issue can happen with ANY type of metal; for instance, a pull tab four inches above, and directly on top of, a dime, may "hide" the weaker/deeper dime signal, and thus your machine will likely "see" -- mostly or even completely -- the signal from the pull tab. However, iron is particularly good at "overpowering" nearby signals. This tendency of iron in particular to "hide" or "mask" any signal from nearby targets is referred to as "iron masking."
So, when iron is under your coil, and your threshold nulls, it certainly may be difficult for your machine to see other, adjacent targets, as these targets will often give a weaker signal than the nearby iron is giving -- but still, your detector has not "shut off." It is still sending and receiving. But, as long as your coil is receiving that strong electromagnetic field associated with the iron, there are two things occuring with your detector -- 1.) the threshold will continue to "null," and 2.) it will be more difficult for the machine to see any other good targets nearby. The "nulling" is an EFFECT of iron being present (and this IRON may cause your detector to miss adjacent, good targets); however, the nulling itself is not the CAUSE of any missed targets.
Obviously, there is a point where the effects of the iron (depending upon its orientation, location, etc. relative to a separate "good" target) diminsh, to the point that your machine can again begin to "see" the signal from a nearby, good target. I believe that this is when you will hear that good target's signal "break" the null, and report to you.
The bottom line is, IRON is what makes your machine "miss" good targets, NOT the "null" itself. The null is just alerting you to the presence of iron (or, again, ANY target you have set the machine to discriminate). When nulling occurs, and it is long and sustained -- lasting for more than just a second or two, then that suggests the presence of more widespread and/or larger iron, as opposed to a one or two second null which suggests a smaller discriminated target.
As a detectorist, nulling can suggest to you that "iron masking" is possible at that point (i.e. there is a chance you are missing some good targets). According to NASA Tom Dankowski, iron masking (combined with depth limitations of detectors) likely "hides" around 80% of all "good" targets in the ground! (Please read this EXCELLENT article... http://www.dankowskidetectors.com/behindthemask.htm ) However, this is just the nature of the beast, NOT an issue that is specific to Explorers. As I understand it, the only things you can do to "fight" the masking issue and hope to find more of those "hidden" targets are A.) move your coil more slowly, to give your machine a better chance to "see" the good target; B.) switch to a smaller coil, which means there will be less iron under the coil at any one time, thus less "masking," and more ability to see the nearby "good" targets, and C.) DIG AND REMOVE THE IRON, so that obviously, the iron's ability to hide a good target has been eliminated! Obviously this is not practical when the iron is pervasive, but digging some of it may help. Meanwhile, slowing down your sweep speed, and switching to a smaller coil are options that some of the more experienced guys on the forum have recommended.
Hope this helps, and if I have made any mistakes here, someone will correct it I'm sure...
Steve
john sullivan
New member
thank you. very thorough
MNCoinhunter
Active member
Thanks Steve...
sgoss66
Well-known member
Elton --
There IS a recovery time -- once a target is "seen," there is a short amount of time until the machine can "reset, just as you say. It's not seconds, though. Put your machine in AM and listen to the rapid-fire signals. It can recover pretty quick. Didn't mean to "challenge" you, just wanted to share what I believe is true.
Thanks!
Steve
There IS a recovery time -- once a target is "seen," there is a short amount of time until the machine can "reset, just as you say. It's not seconds, though. Put your machine in AM and listen to the rapid-fire signals. It can recover pretty quick. Didn't mean to "challenge" you, just wanted to share what I believe is true.
Thanks!
Steve
greasecarguy
New member
Well, I am no expert, but i will tell you that last week I dug a penny attached to a large piece of iron.... dead center of the larger iron piece . I have dug silver coins in the same hole with nails, and i have dug a silver dime with a large iron stake lying on top . I think moving slow, you can hear the goods sometimes but not always.
Go to area were you get the nulling for long time and throw some coins down and sweep them or bury a few a couple inches under and sweep.I know in hot areas were i get nulling for 3 or 4 sweeps at a time i still hear coins come through dont know if i miss any though.
dewcon4414
Well-known member
Elton.... i think you are talking about screen recovery to new targets. You can slow your screen just by using to much sensitivity. The coil works much like a sponge when it hits a target ANY target its like squeezing the sponge... coil shut down. Most of those null do come from disc targets. The machine recovers faster than you think and if you are moving slow and working targets you will get a tone if its in a position for id way before the screen reacts. Its the stages the process is set for. When coil shut down occurs you have a loss of depth... but not total loss.
sgoss66
Well-known member
hey greasecarguy --
Yep -- the "sometimes and not always" part I think is the key. Strangely, iron RIGHT ON TOP of a coin, touching the coin, is easier for a detector to see, than the iron RIGHT ON TOP of the coin but, say, two inches above the coin. Nails in the same hole -- I've done that to. It IS possible sometimes. However, an iron stake on top of a silver dime? That one, I am puzzled! All I can say is, GREAT JOB on that one!
Ohio fred -- throwing the coins ON TOP of the ground is a much easier test for the detector (even with iron below ground), than it would be to take that same bed of iron, and put the coins UNDER -- DEEPER THAN the iron. Again, as I understand it, it has to do with the LOCATION and ORIENTATION of the iron, relative to the coin. These machines do a good job -- maybe as good as any -- in finding good stuff adjacent to iron. I'm simply saying that iron masking hides coins, and "nulling" hints at the presence of iron, and thus the potential for masking. As Bryce, Steve(MS), and others have said, slowing down and moving to a smaller coil can help. Just wanted to throw those thoughts out there. That "behind the mask" article from NASA Tom that I linked, was an eye-opener for me.
Steve
Yep -- the "sometimes and not always" part I think is the key. Strangely, iron RIGHT ON TOP of a coin, touching the coin, is easier for a detector to see, than the iron RIGHT ON TOP of the coin but, say, two inches above the coin. Nails in the same hole -- I've done that to. It IS possible sometimes. However, an iron stake on top of a silver dime? That one, I am puzzled! All I can say is, GREAT JOB on that one!
Ohio fred -- throwing the coins ON TOP of the ground is a much easier test for the detector (even with iron below ground), than it would be to take that same bed of iron, and put the coins UNDER -- DEEPER THAN the iron. Again, as I understand it, it has to do with the LOCATION and ORIENTATION of the iron, relative to the coin. These machines do a good job -- maybe as good as any -- in finding good stuff adjacent to iron. I'm simply saying that iron masking hides coins, and "nulling" hints at the presence of iron, and thus the potential for masking. As Bryce, Steve(MS), and others have said, slowing down and moving to a smaller coil can help. Just wanted to throw those thoughts out there. That "behind the mask" article from NASA Tom that I linked, was an eye-opener for me.
Steve