Metal Detector Circuit - article about Metal Detector Circuit

Navigation Evolves Into Metal Detector Circuit

Most of the modern metal detector circuits operate on the superheterodyne principal, usually seen in receivers for television and radio. This circuit allows for accurate tuning for accurate reception of radio frequency receivers. The metal detector circuit utilizes two separate oscillators with a fixed frequency with the output combined in a mixer. When there is no metal present, these two signals deliver a zero beat frequency.

If the search coil passes over metal, there is a change in the inductance of the coil, which changes the frequency of the second oscillator, altering the beat frequency, which typically is alarmed by a loudspeaker or a light indicator. In the 1950’s, the evolution of the transistor metal detector circuit enabled manufacturers to produce metal detectors small enough and simple enough for children to use. When fabulous old artifacts were uncovered by the truckloads, many manufacturers got in on the act of helping unearth treasures.

Discriminating Detectors End Many Careers

As more companies joined the metal detector market, new innovations were hard to keep up with by the smaller ones and many faded from the picture. Larger companies introduced the discriminatory metal detector circuit, which was supposed to help separate the trash from the treasure. One of the problems discovered was that this type of metal detector circuit would read gold and tin foil as being the same type of metal and when tin foil was ignored, a precious gold item might well be overlooked.

The discriminator also failed to search as deep as the original metal detector circuit designs, and changes were made to the coils. Instead of stacking the two oscillator coils on top of each other, it was found that two ‘D’ shaped coils, back-to-back to form a round circle, could produce better discrimination detection while also penetrating deeper into the ground.

They could also be set to ignore minerals naturally occurring in the immediate area. Today’s metal detector circuits utilize computer chips to hold in their memory specific information about depth, discrimination and sensitivity and use less battery power than their earlier counterparts.

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