Jump to content

Discriminate, Discriminate, Discriminate...but What Exactly??

Recommended Posts

The Gold Monster is sparking my interest in VLF to supplement my detecting arsenal. 

But I have a question - what exactly does a discriminating machine discriminate out?  

I am assuming ferrous and non-ferrous, which in my simple terms means magnetic and non magnetic.  Please correct if wrong.

So on the iron/ferrous side do we have - nails, tin, bottle caps, metal buttons, please add things in here. Where do meteorites fit in?

On the non ferrous side we obviously have gold. But do we also include lead, aluminum, I think most coins aren't magnetic (never tested them), please add things in here. 

With VLF am I still going to be digging every bit of lead, aluminium can and coin?  Or does is narrow down to just gold?  

I have done a brief search on here that got a lot of hits for the word discriminate but nothing specific.  I also know I could google a lot of these answers but I know the very experienced on here will be able to give a very succinct list of what is discriminated out and I can only assume that this is a question many other newbies would be interested to know the answer for.  

I hope you can help. 



Link to post
Share on other sites

G'day Northeast. 

This will help understand it a bit : Not a total listing but enough to give you the idea


4.  Ferrous metals are metals that consist mostly of iron and small amounts of other elements. Ferrous metals are prone to rusting if exposed to moisture. Ferrous metals can also be picked up by a magnet. The rusting and magnetic properties in ferrous metals are both down due to the iron. Typical ferrous metals include mild steel, cast iron and steel. Examples: 1.Mild Steel. 2.Cast Iron. 3.High Carbon Steel. 4.High Speed Steel. 5.Stainless Steel. Rusting. Magnetism.

Some examples of Non-Ferrous Metals are:

  • Aluminium & Aluminium Alloys
  • Copper
  • Gold
  • Silver
  • Brass
  • Lead
  • Zinc
  • ETC.

The Gold Monster 1000 doesn't narrow it down to just gold.

A combination of detect modes ( Gold/iron reject & All Metal ) coupled with the "Gold Chance Indicator" will hopefully help narrow it down some what though.






Link to post
Share on other sites
4 hours ago, Northeast said:

So on the iron/ferrous side do we have - nails, tin, bottle caps, metal buttons, please add things in here. Where do meteorites fit in?

Iron, stony-iron and most chondrite meteorites are ferrous, so when using the Gold Monster 1000 to search for them, you'll want to use the all-metal mode. 

Link to post
Share on other sites

Short answer - it is fairly easy to separate ferrous from non-ferrous, and that is what many prospecting machines attempt to do. There is no way to reliably tell one type of non-ferrous metal from another non-ferrous metal, so you have to dig all the lead bullets, aluminum, etc. to get the gold. Now some details.

Metal detectors are electromagnetic devices. They therefore "see" items that can either conduct electricity (are conductive) or have magnetic properties, or both together.

The most basic obvious difference is the split between items with magnetic properties and items that do not have magnetic properties. We tend to think in terms or ferrous and non-ferrous but it is a bit more complicated than that. Stainless steel for instance can be very conductive but have minimal magnetic properties. It is maybe a bit more to the point to think in terms of "things that rust" and "things that don't rust". Common ferrous items that rust are fairly easy for detectors to deal with, but even then thin flat steel and items with holes, like washers, can present issues. What most prospecting type VLF detectors attempt to do is separate ferrous from non-ferrous. All items like gold, copper, lead, aluminum, silver, etc will read as "good" items on a machine like a Minelab Gold Monster.

Coin detecting machines try to go a step farther. The more conductive an item is combined with the larger the item is can be measured by a metal detector. Aluminum, lead, and gold are less conductive than copper or silver and so read lower on a metal detector identification scale. However, a small gold item reads lower than a large gold item. A small copper item reads lower than a large copper item. A large enough gold item can read like a small copper item. Therefore you cannot tell one metal from another. If every item were exactly the same size and shape you could sort metal directly by their conductivity, but the fact that larger items conduct electricity better than small items throws that out the window. Just like a large copper wire carries electricity better than a thin copper wire, size matters as much as basic conductivity.

However, for certain man made items, like a dime, you can calibrate a response that identifies a dime. The catch always being something else may also read as a dime.


Even more technical, from How Metal Detectors Work

"The resulting received signal will usually appear delayed when compared to the transmitted signal. This delay is due to the tendency of conductors to impede the flow of current (resistance) and to impede changes in the flow of current (inductance). We call this apparent delay "phase shift". The largest phase shift will occur for metal objects which are primarily inductive; large, thick objects made from excellent conductors like gold, silver, and copper. Smaller phase shifts are typical for objects which are primarily resistive; smaller, thinner objects, or those composed of less conductive materials.

Some materials which conduct poorly or not at all can also cause a strong signal to be picked up by the receiver. We call these materials "ferromagnetic". Ferromagnetic substances tend to become magnetized when placed in a field like a paper clip which becomes temporarily magnetized when picked up with a bar magnet. The received signal shows little if any phase shift. Most soils and sands contain small grains of iron-bearing minerals which causes them to appear largely ferromagnetic to the metal detector. Cast iron (square nails) and steel objects (bottle caps) exhibit both electrical and ferromagnetic properties.

It should be pointed out that this discussion describes an "Induction Balance" metal detector, sometimes referred to as "VLF" Very Low Frequency (below 30kHz). This is the most popular technology at the present time, and includes the "LF" Low Frequency (30 to 300kHz) instruments made for prospecting.


Since the signal received from any given metal object exhibits its own characteristic phase shift, it is possible to classify different types of objects and distinguish between them. For example, a silver dime causes a much larger phase shift than an aluminum pull-tab does, so a metal detector can be set to sound off on a dime yet remain quiet on the pull-tab, and/or show the identification of the target on a display or meter. This process of distinguishing between metal targets is called "discrimination". The simplest form of discrimination allows a metal detector to respond with an audio output when passed over a target whose phase shift exceeds a certain (usually adjustable) amount. Unfortunately, with this type of discriminator the instrument will not respond to some coins and most jewelry if the discrimination is adjusted high enough to reject common aluminum trash for example pull-tabs and screw-caps."

A few articles on this website that may help:

Metal Detectors With Reliable Target ID Numbers

FORS Gold, F75 & V3i Tone And VDI Tidbits

The Ferrous/Non-Ferrous Overlap

Tune Out Nails, Your Will Miss Gold!

Target ID / VDI Numbers For Gold Nuggets And Gold Jewelry

Visual Comparison of Some Target ID Scales

Target ID Normalization Details page 4-3 of V3i Advanced Manual

Here is another chart showing typical target overlap issues. Ferrous and low conductive/small items near top, more conductive/larger items near bottom.


  • Like 4
Link to post
Share on other sites

Ashley, Lunk and Steve - thank you. I really appreciate the time/effort you have taken to respond. 

And Steve, your response in particular - I was happy just to know the what but find myself now knowing the why...and actually understanding it :ohmy:

Hopefully it will answer the question for someone else too. 

Thanks again :wink:

  • Like 1
  • Thanks 1
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 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?
    • By ColonelDan
      99% of my detecting is done on central Florida beaches. Since it’s impossible to establish a well stocked test garden at a public beach, I sorta brought the beach home with me and developed my own private beach garden!
      I cut slots in two large empty chlorine tablet buckets at various depths as shown from 2 -16 inches. I then filled one with New Smyrna Beach sand and the other with soil...for the few times I land hunt around here.

      I embedded numerous examples of ferrous and non ferrous targets into paint stirring sticks. I also have several blank sticks I use for gold and silver jewelry as well as artifacts that I don’t want permanently attached to a stick.

      I then insert the target(s) in the slots, each at its desired depth, and start scanning.

      This allows me to rapidly change the targets, depth and relative position of each.  I can now test for sensitivity at depth as well as separation of ferrous and non-ferrous targets in a variety of scenarios using actual beach sand where I do my detecting.
      If I want to test in wet salt sand, I just soak the bucket sand with authentic sea water that I also brought home from New Smyrna Beach...and the Atlantic Ocean never even missed it.  😉
      Works for me.....
    • By Steve Herschbach
      I always have my ears perked up for something new in metal detectors and metal detecting technology. I’m not educated enough to really get deep into the technical side of it, but I have a general layman's knowledge of the subject.

      A couple years ago Carl Moreland, the Engineering Manager for White's Electronics, was interviewed on a radio show. I tripped over a reference to the interview on another forum and checked it out. It is very long, and near the end Carl dropped a bombshell. At least I thought so, but it went unnoticed and uncommented on in the metal detecting online world. I thought about posting it on a forum back then but decided to wait and see what developed. Here is the applicable portion of the interview:

      Relic Roundup Radio Show, January 17, 2012, Interview with Carl Moreland, Engineering Manager, White’s Electronics

      Transcript beginning at 50:57 mark:

      Carl Moreland - “I can mention one technology that we’re working on because the patent has already been published… or the application, not the patent hasn't gone through yet. We’re working on something called half sine technology, which has actually been around since the 1960’s in geophysical prospecting applications. This is where instead of transmitting a sinusoidal signal you actually just transmit half of the sine and you can do that at extremely high voltages and high ? rates and so on. It’s technically not pulse induction but it’s not VLF either and it is a time domain method. And with that we can get really good depth and we can even get target id information and do discrimination and so forth.”

      Can you see why I perked up at that? I am still amazed it did not get any notice at the time. Nothing happened for a long time. Then I got this PM from Rick Kempf recently:

      Sent 29 January 2014 - 09:04 AM

      Was looking for info on my new SD 2100 this AM when I sort of fell down a rabbit hole of old forum posts and emerged reading Whites new patent. About the first thing I noticed was that you were cited in "prior art".

      Here's what they cited: http://www.voy.com/76600/7/475.html

      The patent is here: http://www.google.com/patents/US20110316541

      Is this something you knew about? Just wondering.

      Rick Kempf

      I told Rick, yeah, heard about that. It was the patent finally being granted from the application Carl mentions in the interview. It was fun getting a mention in a patent though I think it was just the examiner studying up on the subject and finding my old post helpful in simplifying the subject.

      For a long time the Holy Grail in metal detecting has been something that combines the target identification of an Induction Balance (IB or more commonly known as VLF) detector with depth of a Pulse Induction (PI) detector. There have been many promises and false starts over the years, and that was one reason I kept the radio interview mention quiet the last couple years. Frankly, I had half forgot about it until Rick brought the patent being granted to my attention. Notice the title:

      Hybrid Induction Balance/Pulse Induction Metal Detector

      A new hybrid metal detector combines induction balance and pulse induction technologies. Target signals are generated from a transmitted wave that has both induction balance and pulse current inducing characteristics and uses pertinent sampling of the receive data. Combining the two data sources provides eddy current target identification while excluding ground permeability and remanence obscuration.

      Is it time to sing Hallelujah? Well, there is a big gap in between getting a patent and bringing a detector to market. Many patents get filed and you never even see something directly related to the patent. Maybe it looked good on paper but does not pan out well in reality for numerous reasons. So just because White's was granted this patent does not mean something is around the corner. However, they have been working on it for over two years already obviously. And it has been some time since White's put something new out. I do not count remakes of the MXT etc as new. So I think there is reason to be hopeful we may see something one of these days.

      John Earle is one of the unsung heros in the industry. He had a hand in many of the best products at Compass Electronics before moving over to White's after Compass went under. To this day I have never used a VLF that goes any deeper than my old Compass Gold Scanner Pro. John was one of the brains involved in that, as well as the White's Goldmaster 3, regarded by many as being the pinnacle of the analog development of that model line. I was fortunate to have met John at the factory some years ago. He is listed as the inventor on the new patent. Half sine technology is also mentioned in an earlier patent filed by White's, again with John listed as inventor at http://www.freepatentsonline.com/7649356.pdf

      Looks like serious stuff brewing. Bruce Candy of Minelab makes mention of half sine technology in a patent application at http://patents.com/us-20130154649.html which makes me wonder about the new "Super Gold Detector" he is working on. But it is this most recent patent by White's that seems to put the finest point on it. Maybe the Holy Grail of detecting is soon to be a reality. The fact it is White's certainly gives me more hope than what we have seen in the past.
      Edit May 2015 - see also White's patent for Constant Current Metal Detector
    • By kac
      Found this patent that Whites filed and got a patent on in 2014 on a hybrid IB/PI machine.
      Curious if anyone heard anything about this. Maybe Garrett will take it on?
    • By NV-OR-ID-CAL-AU
      I know we have had some great advancements in VLF metal detector's over the recent past, but I am hoping that we can keep some of the older design features that seemed to work well. 
      My favorite new technological features being offered in VLF's are Multi-IQ and single frequencies options, fully programmable settings, waterproof, noise cancel, USB chargers, li-ion batteries, Bluetooth headphones, prospecting & coin/relic options, and lightweight. Really a great job by the inventors of these detectors.
      IMHO I hope we do not lose some of the past designs that worked well, such as the ergonomics of the balanced s rod that would separate in three places for backpacking, the hip mountable brain box, the detectors that would not fall over when put on a little bit of an uneven surface, the 6.5 inch elliptical concentric or double DD coils for great access in rocky areas, the 1/4 inch headphone jack, the spare interchangeable battery pack that takes regular batteries to serve as a back-up for the li-ion battery pack, and higher frequencies options.
      I would like to see what else had worked well with other detector user, seems like we are always buying aftermarket parts to retain some of these older features where possible. 
    • By schoolofhardNox
      Not sure where this belongs on the forum, (or if it even belongs here), but this seemed to be the best category to discuss this. Ever since information on the GPX 6000 started to trickle out, I had this nagging feeling something in detecting has changed for those of us who like the thrill of getting to know a new detector. I never would have envisioned the GPX line morphing into a simplified detector. After having the GPX 5000 for a bunch of years now, and using it for relic and beach hunting, I could not imagine relying on a machine that adjust everything for you. I get it that money talks, and when you are a publicly traded company, you go for profit first, and then deny it 😄 And now that there market has switched to an area that probably has very little experience with detectors, the GPX 5000 must have been daunting for them.  So they cater to that market. But I was hoping that a new GPX would fix some of the issues that the 5000 had. I was naive. Minelab has never kept the good parts of their previous machines and just added the the things that needed improvements. On the E trac, the best part of it was the depth it had in finding deep silver,  in long tones, multi. Also the bouncy numbers helped ID deep Indians. When the CTX came out, it lost some of that fluety tone and they tried to straighten out the numbers to a number 12 line. So a two dimensional screen that worked well was transformed into a 2 dimensional screen that bunched most targets on one line. The The EQ comes out and squashes out the numbers even further. So why I thought the 6000 would not do the same is beyond me. I guess I'm disappointing that the "trend" is to make machines where the manufacturer decides on how your machine is going to be set. I hope someone in my area gets a 6000 and is willing to bring it to the beach to compare settings on deep silver. If it wins, then I will eat my words. I know I will get some slack with people saying it's a gold machine, not a relic or beach machine, but to them I would say.... you should be worried when a company controls your ability to fine tune your machine. Thoughts?
  • Create New...