The Manticore and thin wire

I had a VERY disappointing time with my Manticore.

A friend has an underground “invisible fencing”. It is a 20 ga. Solid wire that is buried 3 inch to 5 inch deep. He wanted to extend a corner out to make it bigger.

I thought the Manticore would make a quick discovery of the wire so we could dig it up to splice in the new extension.

Luckily I also took my wife’s Equinox 800….because the Manticore would not hit it….i tried changing sensitivity, ferrous limits, tone, and modes. ---- However the 800 had no trouble locating it. Even when we laid the new wire on top of the ground I could barley get a scratch of a signal out of the Manticore. With the best setting on the Manticore and wire laying on ground I could only get the scratchy signal intermittently, not all along it, but the Equinox did, both on top of the ground and buried, and all hits were clear and solid… as expected.

Tom, this is something like the time I told you about That hunt at the old house, where the Equinox immediately found items where I was just at 15 minutes earlier with the Manticore, which hat no distinct hits and I dug nothing. Except after I adjusted the recovery speed and started getting dig signals (with normal/simple tone it was still softer/more scratchy/mushy sounding —not the bang I am hearing with the Equinox).

Don’t get me wrong, I love the Manticore but …. In my ground (and my friends that is 50 miles away) the Equinox does MUCH better!!! However I do feel the Manticore when it does find a target has better intel with the audio. I use normal with either simple or medium.

I don’t know if I got a defective unit – or – if Minelab NEEDS to do some massive update. MY machine in MY soil has been, so far disappointing. I now have 74 hours and I’m still learning it. I could believe user error BUT I have been trying Factory and every other settings I can think of, including multiple factory resets.

RSmith

Apples to oranges here. I have had my Deus ll for 13 months of regular use and am still learning it. 74 hours is a drop in the bucket. Don’t give up hope as the Manticore is a good detector. Just my 2 cents worth.

Gosh. I wished I was there.......and could see/play/adjust....... to see/ID the problem. I'm quite certain that Manticore should do (at least) as well.
Is the wire "copper"? Or "aluminum"?
I wonder if it ID's as a '1' or a '2'....... which may be being Disc'd out as a hot-rock.

Tom; Sorry I forgot to include that information. it was copper wire. The Equinox tid was around 18, and best I could guess by it's chirping, the Manticore tid was around 38

Carolina; I'm not giving up...in fact today I took the Manticore back to a park that i frequent a lot, I hunted for 4 hours and I was able to pull out two wheaties and a silver merc
RSmith

I am stumped. Is there any chance you could send me a piece of that wire?

I think I have the solution:
The wire itself is very hard to detect. The target frequency of 'long & thin' items is entirely dependant on the 'thin' dimension. The length merely affects the strength of signal you get. For 20 AWG wire, the target freq is in the 100 kHz region [edited figure], so no machine is really going to be hot on it.
What DOES matter, is what the wire is connected to. If it formed a large loop, with the ends shorted together, then it's an entirely different type of target, in terms of both signal strength and target freq. If it's not shorted, but is connected to some electronics gubbins, like a HV transformer, then the 'shorting' effect is unknown.
In order to make detection easier, I recommend shorting the two ends of the wire together, to make a loop.

The Equinox (600/800) TID value of '18' suggests a target freq roughly 8kHz, so clearly there's some 'loop' being created, or it would be reading TID = '1'.

Update: Some back-of-envelope calculations show that a shorted loop would have a target freq of around 2.3 kHz, which would ID around '27' on the Eqx 800. So the actual reading of '18' indicates the loop resistance is higher, by a factor of around 3 times. This could easily be accounted for by, for example 5 Ohms of resistance in the electronics module.



Edited 4 time(s). Last edit at 03/24/2023 08:31PM by Pimento.

Little vid I did.
[m.youtube.com]

One more small video. For better understanding.
[m.youtube.com]



Edited 1 time(s). Last edit at 03/22/2023 10:36PM by tnsharpshooter.

Pimento is exacting/correct.

TNSS....... good demo. Yes...... notice the ID of the straight wire is a ID of '1' (sometimes may bounce to a ID of '2'). Which leads me to say........ some detectors have the extreme low non-ferrous conductor targets report as a iron-tone.........due to hot-rocks ID'ing in the exact same range. For Example: On the Manticore........hot-rocks almost always ID as '1'.....and sometimes as a ID of '2'. Soooooo...........some of the Modes of different detectors ...may be factory config'd to audibly ID these low non-ferrous targets as "iron tone". Looking one step further ...... if you have the horseshoe (iron ID) notched out..... you will not even hear (or detect) the long/thin wire.........because the detectors Mode (from the factory) will ID these low (non-ferrous) targets as: 'iron'.
If you short the ends of the wire together....... you have made a continuous closed loop of continuity ....... of which....is highly detectable.

Same principle with rings. For instance........ the Manticore will detect a man's gold wedding band to 2-feet in an air-test. If you take a pair of cutters (dikes) and 'cut open' the ring........ the ring becomes nearly undetectable. . . . even if the ring is still mostly in a circle. , . , . , . , . , . , . as long as the cut ends are NOT touching. (((This is why you almost never find gold rings with the sizing/solder-joint corroded: "open". They are nearly undetectable))).

This is very interesting for those of us with an engineering background who are not EEs. Would you mind showing your calculations? I suspect the math is not complicated, but, do not know which equations or laws you are using. If it's too much to post, please PM me. Thank you.

Pimento Wrote:
-------------------------------------------------------
> I think I have the solution:
> The wire itself is very hard to detect. The target
> frequency of 'long & thin' items is entirely depen
> dant on the 'thin' dimension. The length merely af
> fects the strength of signal you get. For 20 AWG w
> ire, the target freq is in the 120 kHz -> 170 kHz
> region, so no machine is really going to be hot on
> it.
> What DOES matter, is what the wire is connected to
> . If it formed a large loop, with the ends shorted
> together, then it's an entirely different type of
> target, in terms of both signal strength and targe
> t freq. If it's not shorted, but is connected to s
> ome electronics gubbins, like a HV transformer, th
> en the 'shorting' effect is unknown.
> In order to make detection easier, I recommend sho
> rting the two ends of the wire together, to make a
> loop.
>
> The Equinox (600/800) TID value of '18' suggests a
> target freq roughly 8kHz, so clearly there's so
> me 'loop' being created, or it would be readin
> g TID = '1'.
>
> Update: Some back-of-envelope calculations show th
> at a shorted loop would have a target freq of arou
> nd 2.3 kHz, which would ID around '27' on the Eqx
> 800. So the actual reading of '18' indicates the l
> oop resistance is higher, by a factor of around 3
> times. This could easily be accounted for by, for
> example 5 Ohms of resistance in the electronics mo
> dule.

OK,
Some mathematics about targets, for those curious:

Over on the Geotech1 forum, we did a lot of work on target modelling, testing on VLF and PI machines. For the straight solid wire test, we used electrical grade copper wire, various lengths were tested, 19mm ( 3/4" ) a common one, longer wires helped give a stronger signal to measure. The target time-constant was found to increase in proportion to the cross-sectional area of the wire.
An empirical formula we came up with was:

Time constant, TC = 0.029 * %IACS * d²
TC in microsecs; d = wire diameter in mm; %IACS = conductivity of metal sample, on the standard IACS scale.

So for copper wire 20 AWG: d = 0.81mm diam; %IACS = 102.5
giving TC = 1.95 microsec

To convert to corner frequency, f = 1 / ( 2 * pi * TC )

This gives target freq = 82 kHz [ I was a little off in my earlier post ] , hence the ID reading of '1' on the Equinox / Mandingo.

-------

Many targets can be modelled as an inductor, L in series with a resistor, R. Any circulating current in the inductor will pass through the resistor, losing energy, causing the current to decay exponentially. This is how a PI machine sees such a model. For a VLF detector, the inductor-resistor combination causes circulating currents to lag the magnetic field applied to the inductor. The lag is related to L and R. And it's not just a model: a real physical coil, such as those inside a detectors search-coil, with a resistor connected across its ends, will also function as a target.
Either way, the time constant is calculated as: TC = L / R.

Resistance of a wire loop is calculated from the cross-sectional area of the wire, the resistivity of the material, and the length, ie. the circumference of the loop.
The formula is: R = p* l / A
See this page for more details:
[chemandy.com]
For standard sizes, like SWG / AWG / standard metric series, you can use look-up tables, giving Ohms / metre figures, simplifying the maths.

Inductance is more exotic. The correct formula is:

L = u_o * R * ( ln ( 8 * R / r ) - 1.75 )
or
L = u_o * R * ln ( 1.3902 * R / r )

where R is loop radius; r is wire radius; u_o is 4* pi * 10^-7

This page has the formula and an example calculation:
[quickfield.com]

So, for an example animal fence loop:
Assume diameter is 50 metres. Tables give 20 AWG wire as having resistance of 33.3 milliOhms / metre. The loop resistance is then found as 5.23 Ohms.
The inductance is calculated using r = 0.406 mm; R = 25 m.
giving L = 357 microhenry.
Hence TC = L / R = 68 microsecs
and target frequency: f_c = 2.33 kHz

This would ID as about '27' on an Equinox 800, see below.
Notice that the TC is very insensitive to loop diameter. Essentially, if the loop is made 10% larger, the loop resistance increases +10%, and the loop inductance changes by +11%, so L / R is little-changed.

-------

Calibrating the detector target ID scale to a target frequency ( and vice-versa ) is done by using known frequency / time-constant test targets. With enough readings, graphs can be plotted. In the case of the Equinox 600/800 , there is a precise mathematical relationship observed over the entire 00 to 39 range.
Here's the details, on Steve H's forum, including a chart of the results:
[www.detectorprospector.com]

Hence the Equinox ID of '18' would indicate about 8 kHz for the target.



Edited 5 time(s). Last edit at 03/25/2023 07:43PM by Pimento.

I acquired a piece of that wire as requested.
It is raining pretty hard so I cannot bury it here in my soil to test.

I did however, do an air test in side (before everyone jumps in – I know -- ) BUT I did reveal some things.

1- The Equinox 800 reads it as 1,2,3 While the Manticore reads it as a 4,5,6.

2- His soil must have really played with the TID of the Equinox for to have read consistently 16,17,18 (at his place).

3- Tom may have been right with it shifting to 0 or below????? Would the Manticore shift down while the Equinox shifted up?????? ( I do remember hearing a lot of iron grunts and 98,99 readings, but I just figured it was nails from his big deck he had removed 2 years earlier).

4- both detectors ran stable at sensitivity 21. The Equinox would hit it up to 6.5 inches, The Manticore would only hit it up to 5.25 inches

5- The best setups I came up with on this inside test to get max depth on this wire;

Equinox -- Park 2/ recovery 3/ F2=0/ noise cancel/ ground balance (pushed button while setting stationary on a big box)/ sensitivity 21 (highest stable on the Manticore Equinox was stable up to 23) –---- This was also the same setup used at his house------

Manticore – AT-LC/ recovery 3/ ferrous limits 7-3/ long noise cancel/ ground balance (same as Equinox)/ sensitivity 21–---- This was also the same initial setup used at his house------

Tom if you will email me your address, I will gladly mail the wire to you for your testing.

Some talk has been about the loop being closed ----- it definitely was open---- they broke it while tearing down the deck and they did not know where it was cut. He also wanted to enlarge the dog space so we detected back both sides from the old deck site enough to enlarge that corner.

RSmith



Edited 1 time(s). Last edit at 03/24/2023 10:11PM by RSmith.

Randy........ I just sent you a PM

As I try to Master this Manticore (Tame this beast) I looked over my original post and noticed I left out some important information. While posting it I originally had a lot more written, but when I went to hit the submit button it deleted everything. When I re-wrote it, I mistakenly left some info out thinking I already had it in there.

While I was at his house trying to locate the wire, the only settings I felt were intermittently hitting on it was to bump the recovery speed up to 6 (from 2) / AT-LC / ferrous limits 7-3 / sensitivity 21 / tones I used normal and simple

The Equinox 800 was park 2 / speed 2 / IB F2=0 / 50 tones

The Equinox 800 TID was 16,17,18 ---- Manticore TID was (best I could tell) 34,35,36

I now have 88 hours on the Manticore. I am beginning to feel more confident with it, and I feel the tones (if all settings are correct) are much more revealing than on the Equinox 800. From my short experience with it on the soils in my area … it appears to me, so far, that the setting that makes the most difference is the recovery speed.

At some places a recovery 2 it bangs hard and with defined sounds that lock you up saying dig me, even on deep targets. At other places 2 gives only soft mushy sounding hits …. Something that don’t make you stop in your tracks to double check.

Then there are places like where we were finding the wire, requires Speed of 6 …. But at a park I was at today with 6 the signal is so choppy it sounds like a bad target and needs a speed of 3 for the best sound.

It appears, to me, that both too high and too low give you a sense that there is nothing there to dig.

Is there a fast way to figure which speed setting to use? The way I have been doing it lately, is to set it around 4 until I find a good sounding, deep target … about 4 or 5 chevrons deep , then I stand there playing with it going from 2 to 6 trying to fine the best sound. I then find 3 or 4 more to be sure, or get an average------- there has to be a better faster way.


Tom; The wire is on the way---Thank you

RSmith

Randy......... understand. I'll let you know when I receive the wire sample.........and........my testing results.

There are SO many variables in the real-World that...... each/every target will have a very specific set of 'fine-tuned' settings requirements.....that will differ from every other target. What you are looking for...is an overall 'aggregate' for settings that work the best in MOST applications.
How high the mineralization is ....in your specific dirt, may dictate how high the Recovery Speed needs to be.
The amount/volume of nails also dictates what Mode AND how high/low the Recovery Speed needs to be.
The decomposition status of the nails....dictates how high/low the Iron Bias settings need to be.
The TYPE of EMI dictates which Mode should be used.........nearly regardless of what type of targets you are hunting.
Your learning-curve SPEED.....dictates how moderate-or-aggressive your settings should be.

I wish I could give a simple 'fix all' answer; yet, there are too many variables.

In my dirt/applications/sites....... it is rare that I deviate from a Recovery Speed of 2. If the area is extremely trashy..... I will change my coil-sweep-speed (to 1/3......or even 1/4 normal sweep-speed)....before I change my Recovery Speed settings. In high sink-rate//sandbar Florida....... max depth is critical; hence...... nearly needing to stay at Recovery Speed of '2'.

(((Hmmmmmmm. All of this data should have been on the Manticore thread!!!))).

Randy.......... I just received the thin solid-core (20-Ga) wire. I should be able to test it..... probably within the next 24-48 hours. Will advise.

Randy.......... I just did 'some' preliminary testing of the wire with Manticore. As a stretched-out (one straight length)....... it ID's as 4 or 5 on Manticore........ depending upon which Mode the unit is in. My (initial) concern was: The wire would ID as a '1' (or a 2)...... which would mean.......,,,,,,,some of the Modes may Disc out the wire...... because some of the Modes treat ID's of 1 (or 2) as: hot-rock/Coke.
In many of the Modes....... with Sens on 25.......the distance/depth is about 5" with Manticore. (Response Speed = 2).

Randy....... I think I found your issue.
I just tested your (supplied/mailed) solid-strand wire again..... with Manticore. I placed Sens on 21.....and All Terrain - Low Conductors Mode. Ascertained very good depth on your wire..... with Recovery Speed on '2'. When I switched Recovery Speed to '6'....... the wire became nearly undetectable!!!

IF you are comparing Manticore Speed '6'............ to EQX Speed '2'........,,,,,,,,, you will see Manticore fall flat on its face.
IF you are comparing Manticore Speed '2'............ to EQX Speed '6'........,,,,,,,,, you will see EQX fall flat on its face!
Air test..... AND with real dirt!

Weak conductors will have a severe loss in depth/performance....when you start increasing Recovery Speed. This holds true for EQX, Deus-2, Manticore.......etc..........

Try it with your detectors. Keep Sens the same...... and stay in the same Mode. Change ONLY the Recovery/Reactivity Speed...... and see what happens!!!

NASA-Tom; Thank you for testing …. Yes I agree with your findings. My indoors testing I did before mailing you the wire was just as you described. My start out recovery speed setting was 2, the same as the Equinox 800, but I had to adjust it up to 5 or 6 to start to hear the wire on the Manticore.


To All; Since then I have been doing a lot of detecting and testing each deepish target with different settings to try to figure this out.

I have noticed that when I get into an area where I feel I am not getting good solid hits…I thought to myself that everything sounds more like ground/iron falsing. That got me to looking more at the ground balance and also thinking about tnsharpshooter's video about possibly trying to pump the coil while ‘ground tracking’ to see how fast the numbers move from 0 to the ‘auto ground balance’ number. I even tried using ‘ground tracking’ to see if there was a difference in the final number.

I am still testing this so I may be premature in posting about it….BUT….what I am seeing as of now …I think MY problem in MY soil is the Manticore is not ground balancing as good as the Equinox 800, and my problem is the detector is not fully isolating the target from the ground mineralization.

These are two of my best and worse test findings;
1 – When I had the most trouble--- with the detector I scan for a spot the size of the coil or preferably bigger with both regular detection mode, and pinpoint mode.
1a – Auto ground balance = about 42
1b – use tracking for several minutes = 72
I would try both several times with only a 1-5 number difference.
1c – trying tnsharpshooter's test the numbers changed very rapidly, getting close to the 42 in just 3-4 pumps. Indicating (if he is right), that this ground is highly mineralized.
------ in this test while detecting at the 72 and leaving the ground tracking ON resulted in a very successful hunt, with the targets jumping out at me – and – the falsing iron was very distinguishable from the targets. I was even able to tell by sound a nickel from a beaver tail (pulltab)

2 – When I did not have any trouble ----same procedure as before
2a - Auto ground balance = about 45
2b - use tracking for several minutes = about 45
2c – it would take 12-15 pumps to get even close to 45, (if tnsharpshooter is right- which it is appearing he may be on to something), indicating very mild mineralization.

With scenario 2 if I had 4 chevrons showing, the target would be around 8 inches deep --- But ---- in scenario 1, with 4 chevrons showing, the target is usually only be 3 to 4 inches deep.

I have had several scenarios in between these two, where I could not make auto ground balance match the ground tracking, but the higher ground tracking number would perform better.


One thing for sure --- This is not a glorified Equinox ---- and MUST be treated as a new and different machine. You MUST forget treating it like an Equinox and LEARN from it IT’S ways, language, and needs.

RSmith



Edited 1 time(s). Last edit at 04/06/2023 09:57PM by RSmith.