9/9/26 Report - Some Factors That Affect Metal Detector Readouts. The Complexity of Target ID.

 

Written by the TreasureGuide for the exclusive use of the Treasure Beaches Report.

Left to Right: Large Aluminum Token,  Smaller Aluminum Token, Copper Token, 40% Kennedy Half, 80% Kennedy Quarter, washer.

I planned to do this post a couple days ago, but I didn't get all the good screen photos I wanted. The delay worked out, as is often the case, because I saw something else which changed my focus.

In my previous post I commented on a YouTube video that demonstrated one fellow's "trick" to save time metal detecting. After seeing that video, I stumbled upon another YouTube video explaining the use of the Manticore graphic target-ID display, and although the video was excellent, when the fellow was demonstrating how to use the Manticore display to make dig/no dig decisions in the field he came across a target that gave him a confusing signal. He couldn't determine what the target was, and fortunately, he dug the target.  It turned out to be a coin standing on edge and down about four inches. 

I've done posts and even a video or two in the past on how detectors respond to coins standing on edge rather than lying flat.  The fellow could have used that information.

I've shown several times how the position of coins and other items in the ground affects metal detector signals.  If the coil sweeps parallel to the edge of a coin that is standing on edge, for example, you won't get nearly as strong signal as you would if you were sweeping the coil perpendicular to the edge.  You get a very different signal depending upon whether you sweep one way or another across a coin standing on edge.

Items like that provide a very good signal when sweeping in one direction but produce a very different signal when the coil is swept the other way.  That does not happen for round coins lying flat on the ground.  A good strong signal can get very weak or disappear completely if you change the direction of your coil movement when a target is not round.

The fellow in the video was doing a great job of demonstrating the use of the Manticore display to identify some of the buried targets, but when he got a signal from a coin on edge, he could have gotten a better idea of the buried target if he did something a little differently.  If he only swept the coil in different directions, he would have seen a strong signal when sweeping in one direction but the signal would be much weaker or even disappear if he swept at another angle. That is something I've talked about for decades.  

Below is the screen display for the large aluminum token shown in the photo at the top of this post when token was lying flat on the ground.  As you can see on the display shown below, it produced a very nice signal with a strong and stable conductivity number no matter which direction I swept.  That is the kind of display you'll see when a coin is lying flat.

Large Aluminum Token Readout When Flat.

However, below is the display when the same token was stuck in the ground so it stood on edge.

Readout From Same Aluminum
Token On Edge.

It is the same target, but you see a very different conductivity number and the target ID map looks very different.  Just looking at the two displays, would you ever guess that it was the same target?  I think not.  

When swinging parallel to the edge of the large aluminum token standing on edge, the readout shows a much lower conductivity number AND shows a very different display on the ID map.  In both cases, though, the object showed up on or near the center line..  

I'm only showing one single snapshot though.  You might see a trace or tail leading one way or another from the center line.  The spot might be as well defined as I'm showing here.

When the token was on edge, it presented a smaller surface area to the coil.  If you slanted the token from standing straight up, maybe leaning it at a 45 degree angle, you'd get a stronger signal.  You'd also probably see a trace or tail from the main spot.  I suggest doing your own experiments with that.

I did some tests with the other tokens but won't present all the displays for each of those.  I was going to do that, but as I explained above, changed my focus of this post.  

Below is the short version for some other observations.

The big aluminum token produced a higher number than the smaller aluminum token and the copper token.  Size matters.  Larger objects of the same metal will produce higher numbers than smaller ones if the shape and orientation is the same.  Standing the object on end or even tilting it some will have an effect.  Standing the object on end reduces the surface area presented to the coil, which has the same effect as reducing the size of the object.

The copper token produced a lower conductivity number than the aluminum one.  Anything strange about that?

Copper has a higher conductivity than aluminum.  But there are other factors.  First, many objects have alloys.  They aren't pure.  That is true of pennies as well as many other objects.  Alloys affect both composition and conductivity of targets.  A copper alloy is not the same as an object of pure copper.  Obviously, I didn't test the composition of either object.  The copper token is also smaller than the large aluminum one.  That makes a difference.

All of the coins and tokens showed the dame dramatic effect on the metal detector display when they were stood on end.  

A 90% silver Kennedy half lying flat produced a conductivity number that was about one or two points higher than a 40% silver Kennedy half.  The difference in metallic composition was reflected in the conductivity numbers but the difference was very small.  

  

All of the items shown in the above photo produced relatively high conductivity numbers were shown on the right side of the center line on the Manticore ID map.  I'd consider the range to be relatively small, and nothing in comparison to the difference caused by standing the coins and tokens on end.

I've shown in many posts the effect of target shape on metal detector signals.  For example, long thin targets will often show produce double blip signals when swept over the length (end to end) of an elongated object, such as a nail.  For more about that see The Treasure Beaches Report Direct From Florida's Treasure Coast.: 5/30/11 Report - Memorial Day Issue - Signal Nulling & Glass Detective Work.  

Many things can cause a deviation in a detector's conductivity number and other displays.  Errors will be made.  As I've said many times before, you won't learn about many of the errors made on coins that were never dug.  You never find out about those types of errors.  Most people are happy to simply avoid more junk targets even if it means missing some very good targets.  

 Quite a few years ago I did some tests that revealed relationships between both the surface area and mass of the conductivity numbers produced by different targets.  Here is that link.

Treasure Beaches Report: Pt. 2. (2020 and Beyond). : 2/8/23 Report - Testing Metal Detectors on Dollar and Half Dollar Coins. The Effect of Surface and Mass.

This post took me a long time to finish.  I must have started it about five times.  I couldn't include everything, but tried to include most of what I thought was important.  There are really a lot of factors.  I haven't even touched on some of them.

If you really want to ID a target without digging it up, I recommend at least sweeping over the target from a variety of directions.  As I explained in my previous post, it might be quicker at times to simply dig.  

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There is nothing promising on either the NHC map or the surf charts.

I spent a lot of time on this post and still don't feel like I did a good job.  It was hard to focus and organize because there are a lot of factors.

Good hunting,

TreasureGuide@comcast.net