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Metal Detecting
Decoding Discrimination (Part one)
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Decoding Discrimination (Part one)
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A little about Discrimination

A discrimination control on most (NOT all) machines is simply a dial that will make the detector not respond to, or ignore certain targets.

If you picture the control dial as a single curtain, you will be able to understand the concept easier. If you leave the discrimination fully open, the detector will pick up every type of metal that it is able to 'see', just like looking out a window with the curtain fully open.

As we turn the discrimination up a little (close the curtain), iron will be ignored (the machine will no longer respond to it). Small pieces of aluminum foil such as gum wrappers is the next thing to be covered as we turn the dial up. Next thing to go would be nickels and then pull-tabs.

As we keep turning it up (closing that curtain more), soda caps and then zinc pennies would disappear. Now about the only things left for the detector to respond to are what I call the 'high range metals', silver, copper, brass, and bronze, but NOT gold or platinum (I'll discuss gold and platinum on the next page). Most coins made of copper, clad (sandwiched coins like modern U.S. dimes) and silver will fall into the valuable metals or high discrimination area. Larger pieces of aluminum like drink cans, aluminum siding, car parts and such, as well as heavily rusted iron will almost always show up no matter how high you turn your discrimination up. They are the exceptions to the rule because their signal is just plain too powerful to ignore.

The other type of discrimination control is what is referred to as 'Notch Discrimination'. If we continue to use the curtain analogy, notch discrimination could best be seen as mutiple curtains hung on the same rod.

Say for example, you want to ignore iron, pull tabs and bottle caps, while wanting to see nickels, notch discrimination allows you to adjust the detector to do just that. Much like closing multiple curtains but allowing small open gaps between them. Some machines have a fixed or non adjustable notch or gap, while others allow you to adjust the notches yourself. The Whites Electronics Spectrum series, uses digital discrimination, which can allows unlimited combinations of notch discrimination with just a few touches on a keypad.

Fairly easy to understand isn't it? Now I'll toss in a few other items that make things a little more difficult. A metal detector does not 'see' coins, keys, pull tabs or any other object. What they do 'see' is M-E-T-A-L. They see the metals size, and general shape.

Metal (not coin) detectors respond to the conductivity of metal. The conductivity is determined by a few things: The size of the object, (generally speaking the larger the item of the same metal or alloy, the higher it will be on the discrimination scale). That is why a dime will read lower on the discrimination scale than a quarter or a half dollar, but higher than say a silver 3 cent piece..                                                                              The type of metal (alloys will not respond the same as a pure metal. 10k, 14k 21k and 24k gold of the same size and shape can read differant).                                         The shape (differant styles of pull tabs will not read the same).                                                                              The mineralization of the ground as well as what other metal objects may be close to it (a coin next to, or partially covered by iron will read lower on the discrimination scale).

(continued on the next page)