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