TOMS TREASURES INTERNET MAGAZINE

Beginners Guide to Metal Detectors

Diagrams Included

by Robert Patterson (January 1999)

Who am I and what is this articles purpose

Hello. My name is Robert Patterson.

When first getting into metal detecting I experienced, as I am sure others have, a deluge of info about detectors. During my search for my first detector, I immediately realized that I needed a basic understanding of detectors and their operation before I could make an informed purchase!

I researched the web and other sources. This article is written to help others in my predicament gain a better than rudimentary understanding of metal detectors.

The terminology used does not require a degree in Quantum Physics.

I endeavored to organize the material according to level of importance. Do not skip steps in this article. Skipping steps would be the equivalent to learning to drive a car on the freeway, at rush hour, as the first lesson.

The information pertains to VLF/TR (Very low frequency/Transmit Receive) detectors. This is the most common type of detectors. The principals apply to others with only slight variances.

Step One or How a detector does what it does!

All metals have a trait called conductivity. This is the ability of a metal to allow electrical current, radio frequencies or heat to travel through the metal. Conductivity varies from metal to metal. Copper, aluminum and silver are commonly used for electrical wiring because these metals have higher conductivity than iron or lead or tin. Salt contains a metal called sodium. This is why salt water conducts electricity better than fresh water. Conductivity can be positive or negative, but knowing the difference is not essential in this basic article.

Metal detectors use the conductivity of metal to find metals. A detector "transmits" a radio frequency or magnetic field that travels through air, ground, wood, or other "relatively" non-conductive materials. The magnetic field is "transmitted" from the detectors coil. When this transmitted magnetic field encounters a metal object, a signal is sent back and "received" by the coil. The coil has windings of wire. One winding "transmits" and the other "receives". The "received" message can be heard or seen by the individual operating the detector.

Speakers or headphones allow the "received" message to be heard and a meter or display allow the message to be seen.

Keep these principals in mind. Step two will elaborate on adjustments that need to be made that directly relate to these basic principals.

Step Two--Adjusting the controls so the detector does a good job!

Remember how the signal is "transmitted" through relatively non-conductive substances such as the ground? The word "relatively" is the key word here.

The ground contains metal bearing minerals or solutions of salts to a greater or lesser extent. Not all ground is the same.

The minerals and salts in the ground can prevent the proper transmit-receive operation from occurring properly. Adjustments, either manually or automatically are provided on most detectors to compensate for the conductivity of the ground. If adjustment is not made, then the detector operator will see and hear signals from the ground rather than the rare $20 gold coin he or she is looking for. The following is a basic explanation and of the various controls found on detectors.

Ground Balance

Ground balance is the control which adjust for the minerals in the ground and is adjusted first! If adjusted properly, the ground will be neutral and the detector won't see the ground. Not all detectors have a ground balance knob on the "control box." The vast majority of detectors today are "turn on and go" detectors. There are two types of "turn on and go detectors". The first has circuitry which is adjusted at the factory for an average set of ground conditions. The second type has advanced circuitry which continually readjust for changing ground conditions as the detector is being used. The second is the most common with newer detectors and the preferred type of automatic ground balance. Ground conditions can change many times even over short distances. Some of the automatic ground balancing detectors can be ground balanced manually to help in extreme soil conditions. Detectors with manual ground balance only, require the user to adjust the balance via a knob on the control box. Manually controlled machines can get a little more depth on the average compared to automatic balance detectors. However, improperly adjusting a manually controlled detector will render the detector useless for finding the desired targets. This improper adjustment won't "break" the detector but the detector will not do the job it was designed to do.

Wet salt saturated sand contains a lot of minerals. Most detectors designed for land use will work on wet sand beaches, but lose a tremendous amount of depth due to the salt saturated sand. A number of detectors on the market have a wet or black sand mode button or switch that greatly assist in achieving more desirable ground balancing in wet sand conditions.

Threshold

The threshold adjustment, if present, adjust the level of the received signal that the detector operator hears. This adjustment works in conjunction with ground balancing.

The ground balance if you remember should be neutral.. The threshold is adjusted upward until some noise can be heard and then backed off just a tad. Adjusting threshold at this point will give the operator maximum depth for the ground conditions while eliminating background noise.

Sensitivity

Sensitivity is the throttle of the detector. It adjust the power. Just as it's hard to make a 90 degree turn in your car with the throttle on the floor, too much sensitivity will make your detector uncontrollable. Depending on the detector, the sensitivity control will affect the all metal mode or the discriminate. Some detectors are designed to allow the sensitivity control to affect both. Each detector is different, and it is best to consult the manual of the particular detector to get the best sensitivity adjustments.

If the sensitivity is set to high, the detector operator will receive "false" signals. A "false" signal is an erroneous signal. The detector is seeing or hearing a mirage or mineral laden "hot rocks" or even air pockets in the ground!

Discrimination

Discrimination is the control which adjust the circuitry within the detector to "accept" or "reject" metals of a certain conductivity range.

If you are hunting for silver coins you would adjust the discrimination setting to ignore metals with conductivity below silver. Set as such, you will not "hear" a nickel because a nickel has less conductivity than a silver coin. If you set discrimination to "reject" aluminum pull tabs then you won't "hear" gold, because these pull tabs and gold have almost the same conductivity. If you want to find gold, then you'll need to resign yourself to digging pull tabs!

Many new detectors have display that can visually display targets. The reliability of these displays has a long way to go according to my research. Displays are advancing rapidly but they should not be completely relied upon.

Many experienced treasure hunters have gone back to using detectors without displays.

I have a 1994 treasure magazine with an article about a blind treasure hunter who is extremely successful without displays. The tones a detector operator receives vary and experienced treasure hunters have trained their ears well enough to accurately discern the sound of a nickel, dime, quarter and other items as well as the depth they are located at!

Step Three--Sweep,Pinpointing and Recovery

The three items in the heading above are basics which should be understood for actually using a detector. The following explanations contains a few graphics to help.

Sweep is the path the operator moves the coil over the ground. Overlapping, as depicted, prevents operator from missing areas which might contain an object or target. Sweep can be fast or slow depending on the recovery rate of the detector. Strive to keep the coil parallel to the ground rather than cocked front to rear or side to side.

Pinpointing is the method used to accurately locate the position of the target. Digging a one foot or wider hole, to locate a dime is not acceptable. Sweep in one direction and take note of the point of loudest signal response on this first path. Sweep again approximately 90 degrees from the first sweep. As with the first sweep, take note of the strongest signal response. The point of intersection is the target location.

 Recovery is the length of time a detector needs to respond from target number one to target number two and three etc. If you are sweeping faster than your detectors recovery rate, targets will be lost! Knowing your detectors recovery time is crucial to successful hunting! Testing your detectors recovery time is simple. Place three or more targets in line and sweep your detector past each target. Start the sweep rate slow enough so all targets register a response. Keep increasing the sweep rate until one or more of the targets does not register a response. Slow the sweep rate again until all the targets register. This will be the fastest that you can sweep the detector.

 

Step Four--Summary and "where do I go from here?"

I hope the information provided in this article can be helpful. Valuable additional information can be obtained at metal detecting web site forums Becoming skillful at metal detector use is an ongoing learning process. Test your new detector of choice by planting a coin garden where you live. Listen to the varying audio responses from coins of different metals and different depths. Plant some coins endwise and some flat.

Robert Patterson (January 1999)

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