Detector Depth Test Results

[Ed144]

I've been detecting for both nuggets and artifacts in Arizona. There are many detector options available and I wanted to come up with a way to test and compare detector performance. I installed a detector test range in my back yard that consists of two PVC tubes angled into the ground. My goal is to get some sort of repeatable metric of detector performance that would enable comparisons of VLF, pulse induction, coil sizes, coil types, programming and target type. I've borrowed a few different detectors for the tests or had friends visit and run the tests with their detectors.

It is very difficult to achieve repeatable results that can be used for comparison. There are many variables that need to be controlled. My approach was to consider a target a hit if it was very weak but clear, and to use roughly the same level of target recognition for each test. These test results are subjective and at best have a repeatable accuracy of +/- 10%. The overall goal was to chart test results such that trends in performance could be seen that made sense. Some of the data seems erratic and may need further testing. The data is a work-in-progress and will be updated as other detectors or coils are available.

One of my next goals is to attempt to create a test that might simulate a non-ferrous target hidden among ferrous litter. Perhaps a coin glued adjacent to a couple of nails on a wooden paint stick. I'll be testing XP Deus 2 programming changes to see what might be possible.

I am not a detector expert so I may need correction on some of the trends I am seeing: The pulse induction detectors perform well compared to VLF detectors for most target sizes over about 0.2" diameter. As expected the highest frequency VLFs have the most sensitivity to the smallest targets. The smallest target size the pulse induction detectors hear seems to be set more by the detector timing design rather than coil size. The old Tesoro Lobo Super-Traq is surprisingly good if one replaces the stock coil with a larger Cors or NEL coil.

The details of the test configuration, targets, etc is on the last page of the data. Any comments, suggestions or ideas will be most welcome. Ed, near Tucson, Az.

 

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[cudamark]

The main problem with such tests is the absence of ground interference and the incredible variety of that matrix. Many detectors that air test just fine, are horrible in bad ground or salt water beaches. Conversely, many detectors that don't air test particularly, do quite well under certain ground conditions. Another thing hard to measure exactly is the recover speed of the processor. In target rich ground, that can be more important than coil size along with it's relative sweep speed. I found the best way to compare detectors in a specific area, is to actually swing them all over a target in the ground you plan on detecting and compare signal strength, depth reading (if it has that feature....just one feature why I didn't like the D2), target I.D. stability, EMI rejection, etc, and then dig the target to see which detector did the best overall job. One detector that might work great at one site, might be terrible at another, so, testing can take forever for one person to do. Getting feedback from folks all over the world and under all sorts of sites and conditions are more valuable to me than air tests.

 

[Ed144]

Thanks Cudamark for the comments. I may rebuild my test range. The small tube is angled into the ground at about 34 degrees. It needs to be much longer so that small targets can be glued to a wooden yard stick and slid underground until the target is lost. The larger tube should be used only for large targets. It too needs to be longer. The entire test range needs to be moved to a location that has no EMI so the pulse induction detectors can be better tested.

The ground I'm testing in is typical of the Arizona desert. There is magnetite throughout. One can move a magnet in the dirt and pick up material. I agree with you regarding detectors and target differences. I've seen weak responses from a pulse detector on a very old ferrous target and a VLF detector showed a clear response, and vice versa.

 

[releventchair]

Soil/substrate humidity?

 

[pepperj]

Thanks Cudamark for the comments. I may rebuild my test range. The small tube is angled into the ground at about 34 degrees. It needs to be much longer so that small targets can be glued to a wooden yard stick and slid underground until the target is lost. The larger tube should be used only for large targets. It too needs to be longer. The entire test range needs to be moved to a location that has no EMI so the pulse induction detectors can be better tested.

The ground I'm testing in is typical of the Arizona desert. There is magnetite throughout. One can move a magnet in the dirt and pick up material. I agree with you regarding detectors and target differences. I've seen weak responses from a pulse detector on a very old ferrous target and a VLF detector showed a clear response, and vice versa.

First thing I want to point out is the set up.
You're putting a target in a tube.
Certain detectors just don't do well with air.
Air tests they will detect a given target at a given distance.
Let's say 6 inches.
Now that same type target can be detected in a undisturbed ground.
I can dig the target and it disappeared.
It's either in the loose soil that's in the hole, or just in the next inch or so of soil.

This has happened lots of times over the years.
Minelab explorers hated air between the coil and the ground.
The Deus 1 & 2 have both lost the signal after digging the hole.

I can't give a reason for this but air effects the detection of targets.

So I don't hold much faith in air testing nor certain test gardens.

The only thing is if a person air tests/rubs the items, and the detector doesn't respond in any setting. That pretty well says it won't work digging that target while out detecting.

Gluing a couple of nails beside something actually proves what more than it detects it or not.

No test will prove what a real site will show.

 

[Ed144]

Releventchair: Packed dry sand, dirt, gravel and small rocks in my back yard. Fine magnetite mineralization distributed throughout. Also about 1" of "SaddleBrooke Tan" crushed rock on top. Fairly typical of the Arizona deserts near my home. It is winter here so the humidity was higher than normal, about 28%. Please note that the depths are all relative to my test range setup and will not correlate to data from another range. The data should be fairly consistent across all the detectors and coils tested, except when EMI degraded the pulse detectors. A couple of photos are attached.

 

[releventchair]

Releventchair: Packed dry sand, dirt, gravel and small rocks in my back yard. Fine magnetite mineralization distributed throughout. Also about 1" of "SaddleBrooke Tan" crushed rock on top. Fairly typical of the Arizona deserts near my home. It is winter here so the humidity was higher than normal, about 28%. Please note that the depths are all relative to my test range setup and will not correlate to data from another range. The data should be fairly consistent across all the detectors and coils tested, except when EMI degraded the pulse detectors. A couple of photos are attached.

A few inches is enough for me from the looks of that!
Oh , a guy uses a hammer and screwdriver near Green Valley just to plant a plant...

Spring is the most popular time to detect in my area.
Wet ground.
Very different that dry.
Until you compare...It's not east to explain.

Your tests if at 25% should differ from saturated.

One springtime site I had water in two inch deep targets holes.
Copper cents were ringing up as iron. (High iron content in soil/water.

Wet ground ang big objects...How deep you want to dig? Wet ground and coin on edge vs flat coin..... Next how long the coin has been there will matter.

But experimenting is good!
Duplication, a challenge at times.

 

[Ed144]

Pepperj: I agree, but it is what I could come up with for some comparison testing. I've been volunteering with an archaeology project detecting for artifacts about 480 years old. The "aura" around some of the artifacts is unlike any modern junk detected. One small lead ingot of about 2"x4"x0.5" was heard on my Axiom at about 22" depth in sand but a VLF detector could not see it. Another time the Axiom showed a faint questionable target near a log. When checked with the VLF it was a clear response. If I had more room in my yard I'd bury a number of different targets at various depths and carefully document their locations.

 

[releventchair]

Pepperj: I agree, but it is what I could come up with for some comparison testing. I've been volunteering with an archaeology project detecting for artifacts about 480 years old. The "aura" around some of the artifacts is unlike any modern junk detected. One small lead ingot of about 2"x4"x0.5" was heard on my Axiom at about 22" depth in sand but a VLF detector could not see it. Another time the Axiom showed a faint questionable target near a log. When checked with the VLF it was a clear response. If I had more room in my yard I'd bury a number of different targets at various depths and carefully document their locations.

The Aura/Halo varies.
By material. Time. Moisture. Ambient varied conditions from E.M.I. - to a given units programming and mode.

 

[cudamark]

That's another problem with most test gardens. The target just hasn't been there long enough to duplicate a virgin target that has produced a "halo" around itself. That natural effect makes a target seem bigger and gives a better return signal than one without that halo. As has been mentioned, add an air pocket, or, break up that halo and the target can disappear. A bit more digging and the target will now sometimes be right in your spoils pile.

 

[Carl-NC]

The angled pipe test is about as good as you can do for what you are trying to accomplish. My preference is a 30° pipe so that the slide distance-to-depth ratio is exactly 2, and to keep targets a bit flatter. Ferinstance, with a 45° pipe a coin will produce a signal strength that is 71% of that of a flat coin, whereas with a 30° pipe it is 87%. Not a big deal, but something to keep in mind. The slight amount of air presented by the tube doesn't make too big of a difference but you do want to minimize its effect by using a pipe no bigger than what you really need. I would have a very small pipe (1/4"-1/2" ID) for lead shot targets, a 1" ID pipe for coin targets, and something bigger for relics and the like.

Angled pipes don't work well for target separation/recovery testing because you can't reasonably vary target spacing or set staggered depths. While using a real soil matrix is necessary for testing target depth, it is not really necessary for testing target separation. You can get decent comparative results doing this in air. Below is a simple test jig I use for this. If has two tiers for targets at 3" and 6", and I use a metronome to set a consistent sweep speed.

 

[Ed144]

Thanks Carl. 30 degrees would be a good choice. Thanks for the test jig design. It could be set to many different offset options. Maybe two or three 1" tubes sloped into the ground at 30 degrees. The tubes could be offset vertically by 2" or so. The coin target would be in the top or highest tube with masking ferrous below it. One could also have tubes offset horizontally. I need to find a new place in the yard for Test Range Bravo.

 

[sprailroad]

Wow. Sometimes when I "overthink" things I enjoy, I no longer enjoy them nearly as much. When I go out to "swing a coil", it boils down to, "If I'm meant to find something I will, if not I won't. You just can't cover every square inch of planet earth. Just ONE step to the left, or just ONE step to the right can make a lot of difference, no matter what detector or how many test gardens or how much "tweaking" of the detector settings you do. It's a hobby I've enjoyed for 40+ years? with NO regrets what- so- ever. Listen, keep testing, keep adjusting, detectors are now indeed mini-computers, and many really enjoy that. All is good but remember what it was got you into this detecting thing. The thrill of never knowing what you might find and where, and the pleasure of the "time out" you enjoy out there "somewhere" swinging that coil, and I will add, some of the people that share this same passion that many of us have developed over time, be it people you have detected with or others such as people on the Treasure Net. Hey, have fun with it and enjoy.

 

[Ed144]

I attempted to gather data on the XP Deus 2 13"x11" FMF coil today. It is interesting and certainly better than the 9" round on larger targets. Testing in General program seemed to give good data. When I switched to Gold Field program it appears that I can hear the buried empty tube. When I sweep across the tube from one side to the other I receive a faint repeatable hit I would dig. I poked around in the dirt some but it seems to occur along the length of the tube, at all tube depths. Further testing is on-hold until I can resolve this issue.

 

[Chilli]

Im talking gold here.
I have places that detect the best in dry ground in hot weather.
I have places that are better when wet and cold.
Some places when the clay pockets get wet in winter drive you crazy as they sound like metal targets. Here, on our Victorian goldfields there is no hard and fast rule as to what soil moisture or temperatures are best.
PI sensitivity can greatly vary depending upon coil size and coil configuration.
Least sensitive a DD, better a Mono then best a Spiral or Flat wind coil.
Naturally the smaller coil in each of those types is a touch more sensitive but at the sacrifice of overall depth.
There is a big difference too between some PIs. Take a Whites TDI, its pulse but doesn't come within a bulls roar of a GPX. Garret ATX won't compete either.
One could use those and compare them to say a VLF and think there isn't a huge difference, a difference but not huge. Throw in the mix a 6000, or 5000 with flat winds, or an SDC and the gap widens.
But that's my views of them here where I live. Maybe something to ponder, maybe not