There are two types of metal detectors: tunable induction and non-motion. A tunable induction metal detector has a second coil of wire in its head and allows you to tune the signal to a particular conductivity segment. Its non-motion mode eliminates most of the responses from the detector, leaving only metallic targets. It also allows you to set the notch width so that it only identifies targets of a particular conductivity.
Detecting metals with a metal detector
The most basic principle of metal detecting is to use a detector to search for metallic objects. If a metal is present, an eddy current is created. Every metal has a different phase response when it is exposed to alternating current. The longer the wave, the more conductivity it will have. Shorter waves are more effective in detecting objects with low conductivity, but interfere with high frequency signals.
The first step to metal detecting is to find a legal area to search. Most beaches, parks, and wooded areas are generally friendly to metal detectors. If you’re a beginner, it is best to select a quality detector, read the manual, and practice metal detecting in your own backyard. Ideally, you will want to use a metal detector made specifically for metal detecting. This way, you’ll increase the chances of finding something interesting.
Detecting metals with a tunable induction system
The use of a metal detector dates back to the 1881 shooting of US President James A. Garfield, which resulted in the bullet hitting the President in the chest and lodging deep inside his body. Afterward, the President’s body was discovered, but his bullet had never been found. In response, Alexander Graham Bell cobbled together an electromagnetic metal locator based on the findings of German physicist Heinrich Wilhelm Dove.
Modern metal detectors are equipped with GPS locator technology to pinpoint the exact location of valuable finds. Tunable induction systems use two coils that are electro-magnetically tuned. The coils can be tuned to various frequencies, from three to one hundred kHz. While the tunable induction system may not be the most sensitive metal detector on the market, it is incredibly sensitive, which means it’s likely to pass over a valuable find if you aren’t careful.
Detecting metals with a second coil of wire in its head
A metal detector’s head has a transmitter coil and a receiver coil. When a metal is passed over the transmitter coil, a small electric current flows through the receiver coil and is amplified by the coil. A loudspeaker then produces a sound, signaling the discovery of a metal. The closer the metal is to the transmitter coil, the stronger the magnetic field and the louder the signal.
A metal detector works by sensing changes in an electric field created by the passing electricity through the coil. When a metallic object passes over the metal detector, a second magnetic field is produced around the metal, which the detector picks up. These changes in magnetic field are referred to as eddy currents, and can be used to locate a metal by its magnetization properties.
Detecting metals in the range of the notch width
A metal detector’s discrimination level is the control that determines the size and conductivity of metal targets it will reject. A metal detector with high discrimination will reject all targets that are too large and too small. A detector with low discrimination will accept any metal targets. Using a low discrimination level will limit the target selection to the size and conductivity of the notch. The notch level is an important feature to understand before using a metal detector.
In order to determine the depth of the notch, the IDE probe is moved across the defect. The sensor is located at three mm away. The distance between the notch and the defect is recorded before beginning the notch-type damage scanning process. The results from each step are then recorded. It is recommended to use a level instrument to keep the horizontal relative positions constant. If the notch width is greater than 1.8 mm, the measured results will be close to the true value.
Detecting metals with a VLF metal detector
The type of metal detector you choose will influence the depth of the detection. This is because the closer an object is to the surface, the stronger its magnetic field and electric current will be. However, further below the surface, the magnetic field will be weak and undetectable by the receiver coil. However, a VLF metal detector can distinguish between various metals. Here are some tips for successful metal detection.
When you use a VLF metal detector, you will receive the frequency that is unique to each metal. Inductance and resistance are highly variable and vary by metal type. The VLF metal detector will examine this shift and compare it to the average level for that particular metal. A visual indicator will also alert you if you detect any metal. Once you have found metal, you’ll be alerted by an audible tone or visual indicator.