Jump to content

Recommended Posts

Seems this thread has diverged; @Valens Legacy implies that the equinox should detect magnesium containing bones such as teeth or walrus tusks, while @Steve Herschbach points out that non-conductive items will generally be invisible to the EM search of a detector unless they coincide with a void that alters the ground signal. At the very minimum I can report that the equinox does not in fact detect my cat in any obvious way, even at the highest sensitivity. I think a third possibility exists; perhaps snakes are not generally detectable, which is what you would expect, but these snakes were tagged somehow, perhaps for research and tracking purposes. 

Link to post
Share on other sites

Why is my credibility detector sounding off louder than my metal detector?

  • Haha 1
Link to post
Share on other sites
5 hours ago, ShintoSunrise said:

I think a third possibility exists; perhaps snakes are not generally detectable, which is what you would expect, but these snakes were tagged somehow, perhaps for research and tracking purposes.

Interesting hypothesis.  I did a bit of web searching and snakes are sometimes tagged with RFID chips.  Here is a general overview of that technique (not limited to snakes).

Link to post
Share on other sites

The presence of a metallic element does not mean there will be a response to a metal detectors.  Most minerals contain metallic atoms but most minerals don't set off a metal detector.  Take halite for example.  Halite's common name is rock salt -- a compound made up of a metal (sodium) and a non-metal (chlorine).  Common table salt is a pure form whereas rock salt typically has contaminants mixed in.  I just ran my Equinox over a chunk of halite maybe half the size of a golf ball.  In order to run at high gain (24) I had to use single frequency since I'm at home with lots of EMI around, even in my back yard where I did the test.   All channels notched in and 10 kHz, 15 kHz, 20 kHz, and 40 kHz (EMI quiet frequencies here) all gave no reaction with coil swing about 1 inch or less over the sample.

Metal detectors respond to two things -- ferromagnetic materials and conductors.  The mineral magnetite is an example of a ferromagnetic non-conductor and is well known to cause a signal in an IB/VLF detector.  Metal detectors are sensitive to conductors because the transmitted changing magnetic field from the detector causes an eddy current of charges to flow in the conductor.  In metals those charges are free electrons ('free' in the sense that they aren't bound to any atom).

Ions in solution are also free to move -- that's part of the mechanism in a battery.  Disolve halite in water the sodium and chlorine atoms (sodium carrying one less electron than when neutral and chlorine carrying one more -- thus meaning each one has a net charge) are available to move in solution.  Thus wet salt (e.g. a wet saltwater beach) causes problems for an IB/VLF metal detector.  That's also why some sensitive detectors sound off when you wave your hand closeby (mentioned by Jeff McC.) -- conductive ions from salts on your less than perfectly dry skin.  Damp salty ground in deserts is another example of false signals that IB/VLF's can pick up.

There is a practical limit for something that conducts to be sensitive to a detector, though.  Lightning often strikes trees because they are the least resistive path to ground in a particular location, but I don't think trees set off a metal detector, at least in general.  I swing over large roots and in my soil I don't get signals unless there are metals hiding in or under them (and that does happen occasionally 😁).

Steve H. mentioned ground voids as setting off a detector because the ground balance was matched to solid ground of more/less uniform mineralization and a void is effetively an anomaly -- some of the ground being missing.  I recall reading (can't remember exactly where) Charles Garrett mentioning this in one of his books -- that tree roots can lead to false signals since the root itself displaces ground.  I think you need rather highly mineralized ground for this to show up, though.  As I noted above, in my moderate (2-3 bars or mid-scale on the Fisher F75 and Fisher Gold Bug Pro) ground I don't get falsing going over roots.  Ditto when swinging over mole trails.

 

 

  • Like 3
Link to post
Share on other sites
11 minutes ago, GB_Amateur said:

The presence of a metallic element does not mean there will be a response to a metal detectors.  Most minerals contain metallic atoms but most minerals don't set off a metal detector.  Take halite for example.  Halite's common name is rock salt -- a compound made up of a metal (sodium) and a non-metal (chlorine).  Common table salt is a pure form whereas rock salt typically has contaminants mixed in.  I just ran my Equinox over a chunk of halite maybe half the size of a golf ball.  In order to run at high gain (24) I had to use single frequency since I'm at home with lots of EMI around, even in my back yard where I did the test.   All channels notched in and 10 kHz, 15 kHz, 20 kHz, and 40 kHz (EMI quiet frequencies here) all gave no reaction with coil swing about 1 inch or less over the sample.

Metal detectors respond to two things -- ferromagnetic materials and conductors.  The mineral magnetite is an example of a ferromagnetic non-conductor and is well known to cause a signal in an IB/VLF detector.  Metal detectors are sensitive to conductors because the transmitted changing magnetic field from the detector causes an eddy current of charges to flow in the conductor.  In metals those charges are free electrons ('free' in the sense that they aren't bound to any atom).

Ions in solution are also free to move -- that's part of the mechanism in a battery.  Disolve halite in water the sodium and chlorine atoms (sodium carrying one less electron than when neutral and chlorine carrying one more -- thus meaning each one has a net charge) are available to move in solution.  Thus wet salt (e.g. a wet saltwater beach) causes problems for an IB/VLF metal detector.  That's also why some sensitive detectors sound off when you wave your hand closeby (mentioned by Jeff McC.) -- conductive ions from salts on your less than perfectly dry skin.  Damp salty ground in deserts is another example of false signals that IB/VLF's can pick up.

There is a practical limit for something that conducts to be sensitive to a detector, though.  Lightning often strikes trees because they are the least resistive path to ground in a particular location, but I don't think trees set off a metal detector, at least in general.  I swing over large roots and in my soil I don't get signals unless there are metals hiding in or under them (and that does happen occasionally 😁).

Steve H. mentioned ground voids as setting off a detector because the ground balance was matched to solid ground of more/less uniform mineralization and a void is effetively an anomaly -- some of the ground being missing.  I recall reading (can't remember exactly where) Charles Garrett mentioning this in one of his books -- that tree roots can lead to false signals since the root itself displaces ground.  I think you need rather highly mineralized ground for this to show up, though.  As I noted above, in my moderate (2-3 bars or mid-scale on the Fisher F75 and Fisher Gold Bug Pro) ground I don't get falsing going over roots.  Ditto when swinging over mole trails.

 

 

Great analysis and I agree 100%. Very difficult here to explain why the equinox would detect a snake as a matter of course without introducing metal detecting concepts that don't jive with either physics or our daily experience; I'm going to stick to my tagging hypothesis unless someone else jumps in with another explanation. I saw in another post someone stating their equinox was detecting crabs at the beach; I can only guess that is explainable by unseen tagging or the void hypothesis. At least if I had a snake handy I could settle this right now but unfortunately I am fresh out! 

  • Like 3
Link to post
Share on other sites
5 hours ago, GB_Amateur said:

that tree roots can lead to false signals since the root itself displaces ground.  I think you need rather highly mineralized ground for this to show up

Seen it myself many times.

  • Like 2
Link to post
Share on other sites

When I first gave a response to the question I did a search on the internet and came up with the information I had given. Several articles stated the same thing that I had read also. I did not think of the void that the snake had made, and it sounds like the best answer to the question.

Here is a small part of what I had read from one of the articles.

"Mineralized tissues, such as bone, teeth, antler and horn, are important elemental storage sites in animals. These tissues contain necessary elements, both major, such as calcium (Ca), phosphorus (P), magnesium (Mg) and sulphur (S), and trace elements, such as iron (Fe), zinc (Zn), manganese (Mn) and cadmium (Cd). Most elemental research has focused on the major elements, especially Ca, P, Mg, due to their crucial role in bone metabolism [1]. However, other elemental evaluations and comparisons across tissue types and species are required to more fully understand their biological function."

That is why I made my comment thinking that if a snake was coiled up in such a small ball that it might be possible for a detector to maybe pick it up.

Since I am new at detectors I hope this explains why I gave the answer that I gave.

 

  • Like 1
Link to post
Share on other sites
16 hours ago, ShintoSunrise said:

Very difficult here to explain why the equinox would detect a snake as a matter of course without introducing metal detecting concepts that don't jive with either physics or our daily experience; I'm going to stick to my tagging hypothesis unless someone else jumps in with another explanation.  (emphasis mine)

This is another key point in the investigation of this strange occurrence.  On this forum alone there are millions of hours of detecting experience.  (Not everyone has read this post, but still a lot of combined experience by its viewers.)  Further, a story like this will propogate in the community -- at club meetings, in hardcopy magazines (when we used to have those 😁), on Facebook, on other internet pages and forums....  My participation in this hobby has been mostly confined to reading in the distant past and recently (last 5 years) on the internet, mostly here.  Has anyone seen/read of a similar occurrence?  (You did mention crabs.)

You pointed out that the signals you received were in the pulltab range although you didn't say how tight they were.  If 'sharp' (meaning in space -- not an extended target) and fairly consistent in TID, that would be further evidence of a uniform metal object such as possibly a passive integrated transponder (PIT) tag you hypothesized previously.  (I don't know if those actually have enough conductor to set off a detector.  Could a detector's signal set them off?  Again, more info needed.)  Large animals sometimes are tagged with larger but simpler things -- there was a thread here about bird wildlife tags a while back -- but I doubt those would be used on snakes.

I understand your feelings about accidentally killing one.  But on the plus side, if you decide to avoid this signal in the future at least you'll save yourself digging a lot of worthless pulltabs.  😏

  • Like 2
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Similar Content

    • By GB_Amateur
      This is a topic relevant to every(?) form of detecting -- ground coverage.  I'll list several questions concerns I've had but any replies of course aren't limited to these, nor do they need to address  any of them.  Just tossing out some ideas to prompt further discussion.
      1) What methods and efforts do you apply to ensure full ground coverage in the cases where that is one of your goals?
      2) Is your sweep a straight line path or an arc?
      3) How long is your sweep?
      4) How much do you overlap consecutive sweeps in the direction you walk?
      5) How much do you overlap side-to-side swings when following parallel paths (e.g. when walking two side-by-side swaths in the same direction how much does the left end of one path overlap the right end of the next path or vice-versa)?
      6) Have you ever measured your coverage?  How well do detectors with GPS (e.g. Minelab GPZ-7000 and Minelab CTX-3030) monitor ground coverage to this detail?  Have you used other devices to measure ground coverage.  E.g. I can imagine a drone with camera could provide useful data.  Are there smartphones app that would help quantify coverage?
       
    • By nebulanoodle
      Just dreaming...
      What'dya think? Minelab technology going on the next moon mission?
      X6 must be space-worthy.
    • By AUgetter
      If this question has been addressed elsewhere, I apologize in advance and hope someone can give me a link for it.  I have noticed that other companies besides Minelab are coming out with PI detectors for less than $3K.  How do these detectors compare to the best Minelab detectors for Gold and also relic hunting?
    • By JCR
      On the Anfibio Multi (and I think Kruzer & others) there is a definite step in sensitivity between 39&40 Gain and again between 69&70 Gain. Is this a change in the Internal Threshold? In a way this would be the inverse of the way the F75 adjusts sensitivity according to Mike Hillis.  Regardless, it is a very good set up in difficult sites. Most NM users know about the difference in response speed between 89 & 90 Gain on 3DI. This is different. I had read about these steps in a forum post that quoted Alper of NM. I can't seem to find that post now that I want to re read it.
    • By jasong
      https://patents.google.com/patent/WO2021016649A1/en?assignee=minelab&scholar&oq=minelab&sort=new
      This is the most out of this world Minelab detector patent I've ever read. There is so much here, some very sci-fi like, I don't even know where to start. My takeaway is they seem to be positioning themselves for a drone based detector eventually (main details in this patent could be easily transferred to a drone based platform - IMU, GPS, magnetometer, heads up display, FPV, remote control, robotic/vehicle mount, etc) . That is 100% a guess. But in the meantime, there is some interesting, novel items in the pipeline that we might actually see on a machine in closer future?
      No clue if this is a coin machine or gold machine or if it's something they are actually working on right now or just trying to get control patents on such things for the future which may or may not arrive. One thing is for certain, Minelab is BUSY in the engineering department. A few of the highlights:
      Heads up display over glasses/head mounted display (aka augmented reality). Settings, target visualization, shading of detected/not detected areas (I asked for this specifically 5 or 6 years ago here, awesome to see it in a patent now). Plus a camera showing the coil (why would you need that if not operating remotely as from a drone?) The detector has a camera, IMU (accelerometer) and magnetometer to determine position with accuracy. The IMU tracks the position of the coil in real time in relation to both the ground and the target, and combined with the camera video feed will provide a "visual" of the target in the ground through the glasses/head display, as in form of a heat map which increases accuracy with each pass of a coil over the target. A GPS tracks the machine position to properly map the IMU/coil visual target data on the ground and let's a user see the mapping as they detect. This data is recorded for future historical use and can be shared.  Centimeter accuracy with the visual target heat mapping. Potential operators/users include entities other than humans such as "robots" and "an AI (artificial intelligence) using a metal detector" and this line: "The metal detector may be handheld, mounted on a robotic arm of a vehicle or a robot."  Wireless connectivity to computers and phones, transfer of files containing settings configurations from instructors or expert users Remote control of the metal detector through apps on laptops or phones Ability to upload maps, including detecting data, historic human activity, buildings, or other items that seem to indicate custom mapping capability Internet connectivity, potential control through the internet (again, why if not for a drone type device?) "Teamspeak" to other detecting members in the area wirelessly Visual/spatial discrimination Accurate depth measurement Synthesized audio mode, eliminating noise completely and allowing the detector to "recreate" a synthetic audio stream based on data from prior swings Delayed audio processing (enhanced audio) mode or real time audio mode, ability to seperate multiple close targets, reason for this I venture a guess why below ---> This patent actually seems to be describing a completely new method of RX in a detector. Which is actually similar in some ways to the wacky idea I had years ago of reducing EMI/ground noise by emulating a radio telescope array. But in this case they appear to be describing a fairly ingenuous method of doing something similar with only one coil by monitoring RX of the same target at different points in the swing (with the IMU tracking these points) and combining all those RX signals. In this way (and this is my guess, the patent doesn't explain this), you can form a sort of comparator, gradiometer, or interferometer to seperate the wheat from the chaff, so to speak. If that's what they are doing, then I find it to be brilliant. If not, then I just gave them one hell of an idea to patent for the future. 
      That probably sounds like jibberish to non-engineers. But I want people to understand the brilliance in simple terms. Consider this: EMI is random. At any given point in your swing you'll get noise here, but not there. So if you compare two points in the same swing, you will hear noise one point but not the other point because the "zap" already ended. But you might hear a good target at both points in the swing since it's not random like EMI, it's always there in the ground. So, you can effectively eliminate EMI by comparing what signal is not there at two very close points in the swing, and keep the target since it's always there.
      Similarly, with ground, the ground changes as the alluvium changes since soil is inhomogeneous. But a target is still the target. So, a similar method can be applied to the ground.
      In theory, you could use ideas like this to essentially get rid of the Difficult type timings and keep your gains boosted high, and deal with EMI/ground in this way instead which does not require reducing sensitivity. A totally new, novel approach to RX in a metal detector. The audio processing is very slightly delayed because they are using that time to compare measurements at a few different coil positions before letting the audio processor signal that there is a target present. That's my guess. If that isn't what they are doing, then someone else should patent that and thank me for it later when Minelab buys it. Either way, they have something totally new in the RX department here. And the future of detecting looks bright and interesting to me still.
    • By WhiteRabbit
      Hello, now here’s an opener that might just get me banned on my first post!
      Bear with me, my intentions are pure :)
      Does anyone know if it would be possible to jam an MD signal? The reason I ask is to combat the evident problem we have in the UK with “nighthawks”, illegal detectorists.
      Over here, any landowner can grant permission for detecting on their land (with caveats, known historic sites are protected by law). What often happens is that such a permission is granted and a detectorist innocently sets about his / her business. Someone less scrupulous spots this person and assumes there may be something important there, so shows up at night with a couple of friends and the landowner awakens to a field / lawn full of holes, then bans metal detecting.
      Historic sites are also looted.
      Just an off the wall question, how tricky would it be to build a device to block this on a piece of land? Anyone any ideas?
×
×
  • Create New...