get to know the technology behind metal detectors and how they work.

A typical metal detector and it's components are shown in the diagram below. How a metal detector works depend on the type. There are three types of metal detectors based on it's detection technology. These are : * Very low frequency (VLF) * Pulse induction (PI) * Beat-frequency oscillation (BFO) Very low frequency (VLF) This is probably the most popular detector technology in use today. In a VLF metal detector, there are two distinct coils:

The alternating current moving through the transmitter coil creates an electromagnetic field. The polarity of the magnetic field is perpendicular to the coil of wire. Each time the current changes direction, the polarity of the magnetic field changes. This means that if the coil of wire is parallel to the ground, the magnetic field is constantly penetrating into and out of the ground. The generated magnetic field induces metallic objects to generate it's own magnetic field. It is this weak induced magnetic field that is picked up by the receiver coil. Therefore, when the receiver coil passes over an object giving off a magnetic field, a small electric current travels through the coil. This current produces the same frequency as the object's magnetic field. The coil amplifies the frequency and sends it to the control box of the metal detector, where sensors analyze the signal.VLF metal detectors are consider good discriminators in it that they are able to distinguish different metals.

PI Technology
The next but less common form of metal detector is based on pulse induction (PI). Unlike VLF, PI systems may use a single coil as both transmitter and receiver, or they may have two or even three coils working together.

This technology sends powerful, short bursts (pulses) of current through a coil of wire. Each pulse generates a brief magnetic field. 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.

How it detect metal is this. If it is over a metal object, the pulse induces an opposite magnetic field in the object. When the pulse's magnetic field is ending, the magnetic field of the object makes it take longer to completely disappear. This process works something like echoes. If you yell in a room with only a few hard surfaces, you probably hear only a very brief echo, or none at all. However in a room with a lot of hard surfaces, the echo lasts longer. In a PI metal detector, the magnetic fields from target objects add their "echo" to the generated pulses, making it last a fraction longer than it would without them.

PI-based detectors are not very good at discrimination because the reflected pulse length of various metals are not easily separated. However, they are useful in many situations in which VLF-based metal detectors would have difficulty, such as in areas that have highly conductive material in the soil or general environment. A good example of such a situation is salt-water exploration. Also, PI-based systems can often detect metal much deeper in the ground than other systems.

BFO Technology
It is known as beat-frequency oscillator (BFO) and most basic way to detect metal. In a BFO system, there are two coils of wire. One large coil is in the search head, and a smaller coil is located inside the control box. Each coil is connected to an oscillator that generates thousands of pulses of current per second. The frequency of these pulses is slightly offset between the two coils.

As the pulses travel through each coil, the coil generates radio waves. A tiny receiver within the control box picks up the radio waves and creates an audible series of tones (beats) based on the difference between the frequencies.

If the coil in the search head passes over a metal object, the magnetic field caused by the current flowing through the coil creates a magnetic field around the object. The object's magnetic field interferes with the frequency of the radio waves generated by the search-head coil. As the frequency deviates from the frequency of the coil in the control box, the audible beats change in duration and tone. The simplicity of BFO-based systems allows them to be manufactured and sold for a very low cost.They can even be a DIY detector. But these detectors do not provide the level of control and accuracy provided by VLF or PI systems.

We will now find out How To Buy A Metal Detector?

Enter your search terms Submit search form