Thursday, February 19, 2009

Buying a Metal Detector

There are a number of factors one needs to take into consideration when buying a metal detector.

As there are many different types of metal detectors, probably the first factor to consider is, what are you going to use it for? Of course, in this instances it is for the detection of gold. Even then one can get metal detectors that specialize in detecting precious metals, or one can get a more general one if one is going to use it to detect other things such as old coins for example.

Then there is the consideration of who is going to use it? Is it just yourself or perhaps the whole family? If children are going to use it then one might need to consider a shorter pole and a lighter model for them. Children also seem to pick up on the technical aspects rather quickly these days (after all, who sets up your video or CD machine) so that tends not to be an issue. One can also get a kids metal detector.

If you are a new user then perhaps a simpler model rather than the more sophisticated may be suitable to start off with. There are hundreds of different models to choose from and each have their own instructions on how to use them. The question then is, which is the most suitable for you? Asking a friend will usually only elicit the model that they prefer and have found suitable for them. Most metal detector users tend to stick to one model or, at the best, brand of metal detectors and so have little of any experience of other brands and models.

Some brands of metal detectors are heavier than others. This may be important if the person using it is slight rather than bulky.

Some require more technical expertise than others. Some have a bigger or different 'swing' than others also.

As a general rule the more expensive the detector the more features and refinement it has. So how often do you intend to use it may have a bearing on your purchase. If you use it once a year just going recreational gold prospecting for fun, then a simpler model may suffice. But if you intend prospecting on a more serious note on a regular basis then a more sophisticated detector will be more worthwhile.

Of course your budget will have something to say about how much you can spend on a metal detector and that, again, will depend on the purpose for buying one. Whether recreational, or for a more serious hobby.

The main criteria is probably to buy the best metal detector you can afford which will detect gold at a reasonable depth and which is not too heavy or complex to use.

A good way of doing this is to write down the features you need based upon the points listed above and then list the metal detectors that fits these requirements the most. One can then check for reviews of those detectors and using them as a guide pick the detector that best suits your requirements and which is affordable for you.

Buying a metal detector is not as complex as it sounds and when you have been out gold prospecting with a metal detector, will likely get the bug. It is likely it will not the last gold metal detector you buy!

Tuesday, February 17, 2009

How to Use a Metal Detector

It is very important to know how to use a metal detector to get the best use out of it.

When you get a metal detector it is in pieces. Usually it will be a simple assembly job to screw or fit the pieces together and all metal detectors come with an instruction manual that includes this information.

Once you have your metal detector assembled the instruction booklet will tell you how to use it. The controls will vary with each make and model but there are some basics to using the metal detector it is useful to know and which will help you understand how to make the best use of it when prospecting for gold.

Getting used to the controls and how the information is displayed and indicated is the first step. It is very tempting, when you have assembled your first gold metal detector, to zoom out into the garden and give it a whirl. But this can be confusing as the detector is highly sensitive and you can end up confused by what you see and even hear.

A metal detector detects objects through the magnetic field generated by the coil at the bottom of the detector. In fact there are usually two coils, one for generating the field and the other for detecting any changes in that field caused by objects that enter that field.

The controls are used to filter out unwanted objects or to change what you want to detect or give information about what is being detected. How this information is given to you will depend on what settings you apply to the detector.

It is a good idea to practice using the metal detector at home before you take it out to do some gold prospecting. You can use a benchmark at home to start with. This is a simple way of understanding how your metal detector works.

Using a wooden table place your metal detector on the table.

Place in a row a number of metal objects that you might find when out prospecting for gold.
Bottle Top
Can Tab
Coin (US coin)
Foreign coin
Something gold, like a gold ring.
Some copper
Something silver
Take each object in turn and pass it under the coil. You will find there is a different sound for each object. Note these sounds down as they will help you to determine later when you are prospecting, what you have found when that sound is heard.

Try the same thing at different settings on your detector. You will notice sometimes the sound changes. You can apply filters also so that you can filter out the sounds created by such objects as nails, bottle tops etc. This makes it much easier as you then will not have to waste time digging out something of no value.

How you use the detector will make a difference also. Slow sweeps close to and along the ground usually produce the best results. Some objects can be buried quite deeply. Many modern metal detectors will display the depth of the object depending on the quality and sophistication of the detector.

Also there is such a thing as ground balance. Sometimes the ground, such as sand, is mineralized, which is to say, there are minute Specks of metal or metals mixed with the sand and this can interfere with the results obtained by the metal detector. So a ground balance filter should be incorporated in the detector to filter this out.

Lastly really following the manual supplied with the detector and practicing so that it is second nature will really help you to understand how to use a metal detector so that you get the best possible use and the best bang for your buck.

Saturday, February 7, 2009

How Metal Detectors Work

Knowing how metal detectors work will help one choose the right detector for your purposes and be able to use it more effectively.

Operating a metal detector is a simple process. Once you have turned the unit on, you simply move the coil back and forth slowly over the area you want to search. When the coil passes over a target object, say a small sliver or nugget of gold, for example, an audible signal is produced by the control unit to alert you that something has been found.

The more advanced the metal detectors the more it can pinpoint the type of metal it has located including the exact spot and depth.

A metal detector is usually fairly light-weight and is made up of the following parts:
A Stabilizer. Some of the more sophisticated detectors will have a stabilizer which is used to steady the unit as you sweep from side to side.

A Control box, of course which contains the circuitry, microprocessor, controls, speaker, and batteries.

The shaft. This connects the control box and the coil; Try to get a detector with an adjustable shaft so it can be set at a comfortable time for your height.

Search coil. This is the part that actually senses the object, also called the "search head" or "loop" and even, "antenna".
All metal detectors use one or more of the three following technologies:
Very low frequency (VLF)
VLF Phase Shifting
Pulse induction (PI)
Beat-frequency oscillation (BFO)
Very Low Frequency
VLF is also called induction balance, and is probably the most popular system used today. This is the system that uses two coils. A transmitter coil and a receiver coil.

In the Transmitter coil, an alternating current is sent along this wire, first in one direction and then in the other, thousands of times each second. The times the current changes direct each second is the frequency of the unit. The receiver coil is designed to act as an antenna and pick up to pick up frequency changes caused by metal objects entering the magnetic field produced by the first coil.

A metal detector can tell from the variations in the magnetic field detected by the detector coil how deep an object is and even, to a large extend, what sort of metal it is.

Different metals have different resistance levels to electricity. Also some conduct electricity better than others. Copper, for example, is an excellent conductor of electricity. Lead is a poor conductor. So the resistance to conducting electricity affects the magnetic field as does the depth of the article. The deeper it is the longer it takes to affect the magnetic field.

All these factors are picked up and analyzed by the metal detector and the information is displayed on the control panel.

Most metal detectors these days use integrated circuitry, like a mini computer, to process the information it received from the coil and displays for you to read.

VLF Phase Shifting
VLF Phase Shifting is the method by which a VLF Metal Detector can tell the difference between different metals. This uses what is called phase shifting. A phase shift is the difference in timing between the transmitters coil’s frequency and the frequency of the object.

This discrepancy can be the result of a couple of things.

Inductance – The is the speed at which a object conducts electricity. The easier it is to conduct the slower it is to react. Think of inductance as a deep river: Change the amount of water flowing into the river and it takes some time before you see a difference.

Resistance – An object that is reluctant to conduct electricity has a high resistance. Plastic and ceramic will not conduct it at all, hence is used as an insulator. Various metals all have different levels of resistance.

An object that has a high inductance, therefore, is going to have a larger phase shift because it will take longer to change its magnetic field. An object with a small resistance will have a smaller phase shift.

So your metal detector can distinguish between various metals by analyzing the phase shift of those objects you detect, and will display the results for you on the metal detectors display panel.

This means it can discriminate and this is useful when you are working an area that may have mineralized sand as you can filter out the results caused by the mineralized sand as well as single objects, junk such as bottle tops, pull tabs and so on.

Of course this is all done in fractions of a second and all you will see are the result displayed by the detector.,

PI Technology
Less common but still very useful is the metal detector based on PI technology. PI means Pulse Induction.

As you might have guessed, this uses a pulse to detect object rather than a magnetic field and so uses only one coil to perform the purpose of detection.

A PI detector sends out a pulse of current through the coil of wire. When it does a brief magnetic field is produced. When the pulse ends the magnetic field reverses polarity (remember all magnetic fields have a north and south pole?) and this collapses very fast and results in a sharp electrical spike. That spike then causes another current to run through the coil. This is very fast and lasts just 30 microseconds. Another pulse is sent and the process repeats. Usually about 100 or more times per second.

This technology sends powerful, short bursts (pulses) of current through a coil of wire. Each pulse generates a brief magnetic field. When the pulse ends, the magnetic field reverses polarity and collapses very suddenly, resulting in a sharp electrical spike. This spike lasts a few microseconds (millionths of a second) and causes another current to run through the coil. This current is called the reflected pulse and is extremely short, lasting only about 30 microseconds. Another pulse is then sent and the process repeats. A typical PI-based metal detector sends about 100 pulses per second, but the number can vary greatly based on the manufacturer and model, ranging from a couple of dozen pulses per second to over a thousand.

This is rather like echoes. You remember the difference when you talk or sing in a room with a hard surface compared to one with soft surfaces? A bathroom is a good example. The sound in a room with hard surfaces lasts longer than in a room with soft surfaces. That’s why your voice sounds so wonderful in the bathroom when taking a shower but not quite so good in the living room with the carpet and soft drapes. In a PI metal detector, the magnetic fields from target objects add their "echo" to the reflected pulse, making it last just a fraction of a second longer than it would without them. Then a sampling circuit monitors the length of the reflected pulse sand compares that to the length expected. The circuit can tell the difference between the decay rates of the reflected pulse sand deduct if there is a metal object interfering with it.

BFO Technology
Another system to detect metal is by the use of a beat-frequency oscillator (BFO). In a BFO system, there are two coils of wire. A larger coil is in the search head, and a smaller coil is located inside the control box. Each coil is connected to an oscillator generating thousands of pulses of current per second the frequency of which is slightly offset between the two coils.

The coil generates radio waves as the pulses travel through each coil and a tiny receiver in the control box picks up the radio waves. From these it then generates and creates an audible series of tones (beats) based on the difference between the frequencies.

Simply put, when the coil in search head passes over a metal object, such as a gold nugget, it creates a magnetic field around the gold nugget. This magnetic field interferes with the frequency of the radio waves generated by the search-head coil and this causes a change in the audio tone.

The BFO system is very simple and so they can be manufactured at a very low cost.

Last Word on Metal Detectors
The metal detector you decide to use will depend primarily on your budget, the purpose you will use it for and how often, but having the above information and knowing how metal detectors work will go a long way to buying and using the right metal detector for you.

Sunday, February 1, 2009

Gold Metal Detectors

A gold metal detector is a machine designed to locate gold underground. There are many types of gold metal detectors with varying degrees of refinenmint and complexity but they all operate on the same basic principle.

How Does a Gold Metal Detector Work

A gold metal detector, like any other metal detector, operates by generating an electromagnetic field which is swept along the ground. As it does so, any gold found will affect the electromagnetic field by changing it and this change will be displayed for the operator to see and also may be indicated by an audible sound produced by the metal detector..

Inside a metal detector are two sets of copper wire windings. An electrical current is passed through one of the windings and this creates the electromagnetic field. This is called the transmit winding.

As metal conducts electricity, any metal object brought into the field will alter it and this alteration is picked up by the second winding, known as the receive winding. This is then sent to the control box which the operator can use to control the types of metals he or she wants to detect. This information is then displayed through a meter or LCD display and, often, with an audio signal. The more sophisticated the detector the more information is displayed.

There are various refinements to metal detectors designed to filter out unwanted metals and give a signal on the wanted metals only. This is called discrimination and is achieved by the detector being set for a specific level of conductivity. Different metals conduct electricity in different degrees. Silver is an excellent conductor of electricity for example whereas nails are a very low conductor of electricity. Each metals conductivity is known of course and so a metal detector can be set to detect gold or silver and reject any others. The size of the metal found is not particularly important in this case. It is just the ability or the ‘willingness’ of metal to conduct electricity that is detected.

A detector will often react to minerals in the ground or "mineralized ground" as it is called. These cause false signals and is referred to as "ground noise" . Any metal detector you buy should have a "ground balance" control to tune out ground noise. The best metal detectors can eliminate virtually all ground noise.

Some detectors can detect metal quite deep. This will depend on the quality of the detector as well as the way it is used. It also depends on the size of the object. A large nugget of gold deeper underground will be detected whereas a small speck might not be.

Types of Gold Metal Detectors

There are many types of metal detectors. One can buy a cheap detector which has little or no discrimination or one can buy the very best metal detector at the top of the range which has all the bells and whistles. Much will depend on your budget as the cost of a gold metal detector can range from 50 dollars for a very basic simple metal detector to well over a thousand for a more sophisticated model. I have even seen one for close to 5000 US dollars (the GPX-4000 Metal Detector). There are perhaps 20 or so manufacturers of metal detectors in the US with hundreds if not thousands of detectors to choose from. You can even buy metal detectors for use under water. Good for finding sunken treasure.

The type of detector you buy and use will depend primarily on the reasons for using it and the budget available. To go fossicking for gold, a reasonably sophisticated metal detector is needed. As in anything else one buys, one gets what one pays for. To prospect for gold with a gold metal detector you need a detector that can detect small particles of gold as well as the larger one. Also able to detect at least 12 inches underground and is able to filter out or discriminate gold from other metals as well as eliminate ground noise.

Gold Detecting Tips
Some useful detecting tips when using a gold metal detector include:

Go low. As close to the ground as possible. This will improve your chances of finding something buried further down. The electromagnetic field is only so big, unless you have a really big super duper detector, but even then there is still a limit as to how far down it can detect, so the lower you can sweep the better.

Go slow. Your sweeps on the surface of the ground should be slow. Do not be impatient. It is easy to miss a small gold nugget if you sweep too quickly.

Ground Balance is important. As mentioned before, this is where there are natural minerals in the ground beneath the detector. You need to ensure you have a detector that will compensate for this. The automatic tracking feature some detectors have is a good idea as the detector then maintains the ground balance setting as you sweep over varying grounds.

Another useful tip is to research old gold prospecting areas. Doing some research can be invaluable as you could find old maps, records that indicate some gold was found in certain areas. Old surveys and geological reports can be a good source of information also. You do not have to limit yourself to established gold fields. Old small fields used by old timers (without a gold metal detector) long ago can be quite lucrative. Although they may have gold there, they are generally too small for mining companies to economically find and process gold. But they are ideal for the small prospective gold fossicker and can be quite lucrative.

If you find a spot that is giving you some results. Slow right down and do a very thorough sweep several times. It is better if your detector is set a bit too sensitively, especially if your metal detector can discriminate very well. Try and keep the setting fairly low. You may dig up more rubbish that way but are unlikely to miss any potential gold deposits or gold nuggets. And you never know what else you may find! It is not uncommon to find old coins and other potentially noteworthy items.

If you find any rubbish or trash, it is a good idea to remove it and dispose of it in an environmental fashion so you do not keep detecting the same rubbish over and over again.

Make your detector comfortable. Adjust it so that it is easy to hold and use and you will be less tired at the end of the day. Take frequent breaks also and look elsewhere, such as the horizon for example to reduce possible eyestrain.

Lastly enjoy yourself. Gold metal detecting can be a healthy outdoor sport!