Are there any electronics engineers here in these forums?

[SilverFinger]

Ok, it's official. I'm obsessed with MD'ing. I've even considered a career path change in hopes of learning electronics engineering to understand and possibly build a detector somewhere down the road. My math skills are what's holding me back.

I understand the concept of whats used for a discriminator circuit. Phase shift or conductivity response times of different metals cause a certain definable 'lag' in how the transmit and receive coils respond to different metals in a metal detector. That's why motion is required when discriminating.

I am wondering if there are other properties of metals (other than phase shift) that can be analyzed using info from the electromagnetic field the detector generates. I mean, you can't stick an ohmmeter in the ground, I know, but can resistance (for instance) be measured somehow without touching a target?

The age old problem of losing gold and even nickels when you knock out the tabs and other junk. There's got to be another technique to analyzing metals that can definitely say "nickel, gold, aluminum, foil, iron, pull tab, school bus...", etc.

I'd also like to see an add-on accessory for the old analog detectors. Something that can connect between the coil and brainbox that would inject some digital voodoo into target ID'ing by reading the incoming info from the search coil. A balance of old and new.

I wish I was smart, 'cause I'd invent the perfect metal detector!

 

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[Tom_in_CA]

check a forum called "metal detecting equipment". It is specifically for techno-buffs.

 

[flyinguy]

i wish i was smart 'cause i would invent the perfect printing press!

 

[Silver Fox]

Contact BOUNTY HUNTER and request contact information for George Payne. You can't do better.

Silver Fox

 

[lgadbois]

Electromagnetic metal detectors use three different signal properties to identify the target. The three properties are frequency, amplitude, and phase.

The first metal detectors used two oscillators with a single detection coil. One oscillator was fixed in frequency, while the other used the detection coil for determining the oscillator frequency. The oscillators were tuned to nearly the same frequency, and the beating of one against the other would generate a audible tone. When the detection coil would pass over an iron target the tone would change in pitch in one direction, and non-iron would cause the tone to change in the reverse direction. This was a BFO type detector (beat frequency oscillator).

The T-R (transmit receive) detector uses two coils in the detection head. One coil to radiate the signal, and a separate coil to receive the signal that is coupled back from the target. With this system a amplitude threshold could be set, and a discriminator would allow the user to ignore iron targets. Later models of this analog design allowed target identification and a variety of other user settings such as ground balance, sensitivity, etc.

The new digital models offer features to accurately measure signal strength and metal type. Some offer multiple frequency designs that give the best overall depth and detection with a wide variety of soil conditions and metal types. The transmitter, receiver design, and digital circuits are very sophisticated, though the principles of operation are the same as the best of the older analog detectors. A good analog detector may find as much as one of the new digital detectors in the hands of an experience operator.

Target detection on the new units is wonderful, and can save a lot of work by screening unwanted junk. If you want to maximize your finds, you will need to operate in an all metal mode and dig everything.