How Do VLF Metal Detectors Work? No ratings yet.

Metal detector on sand

Before we take a look at how VLF metal detectors work, it’s a good idea to look at the different types of metal detectors out there:

  • Beat Frequency Oscillation metal detector
  • Pulse Induction (PI) metal detectors
  • Industrial metal detectors
  • Very Low Frequency (VLF) metal detectors

Read on for a description of the different types:

Types Of Metal Detectors

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One of the most common kinds of metal detectors is a Beat Frequency Oscillation metal detector. It’s a handy metal detector, which is able to detect metals up to 2 feet underground. In addition, it uses oscillators that provide a frequency to the rings on its base to detect metal.

There are Pulse Induction (PI) metal detectors, which are high grade and specific purpose metal detectors. They’re employed to look deep into the surface for gold, treasure and metal relics from the past.

Then, there are the industrial metal detectors. Used primarily for security purposes, they’re used mainly as doorframes at entrances at airports and secure buildings.

And then finally, we have Very Low Frequency (VLF) metal detectors. They are the most commonly used metal detectors in the world. A VLF metal detector is used for a wide range of applications due to the technological advancements exhibited by it. In order to understand how VLF detectors work, we’re going to take a look at all the components of the metal detector and the role they play.

Once you've learned how a a VLF metal detector works, check out our review of the best metal detector.

Parts Of A VLF Metal Detector

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Transmitter Coil

This is the outer coil on the base of the VLF metal detector. It consists of a coil of wire, which has electricity running through it in one direction and then the other at a rate of thousands of times each second. The rate at which the electric current passing through it is reversed determines the operating frequency of the transmitter coil.

It plays an important role in how VLF metal detectors work. The flow of the current through the transmitter coil induces a magnetic field whose magnetic poles point towards the ground. When the current is reversed, the magnetic poles are directed upwards. Any metallic object that conducts current will see the magnetic fields induce current. That influences the magnetic field.

Receiver Coil

The receiver coil is also placed on the base of the VLF metal detector. The role the receiver plays in how VLF metal detectors work is that it acts as an antenna to pick up the frequencies coming from metallic objects in the ground and amplify them.

This coil is arranged in a way that nearly the whole current which would flow because of the transmitter coil is cancelled out. This means it can easily pick up the output by target metallic objects and amplify them without interference from the transmitter coil.

Microprocessor Control

Microprocessor control consists of a complex electronic circuit, which handles all the control functions required to process the transmitted and received frequencies for VLF metal detectors. It uses a program, which allows you to change the settings based on what you’re searching for.

You can select preferences for everything, from coin hinting to prospecting and even relic hunting. The microprocessor takes on the task of making the necessary adjustments to help you search for those items.

Important Concepts

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Discrimination

Metallic objects made of different materials and sizes give their own characteristic responses to the magnetic waves passing through them. Their ability to discriminate between the metallic objects using their phase shift (the difference in timing between transmission from the transmitter coil and the frequency of the target object) is a major part of how VLF metal detectors work.

An object with a larger phase shift means it conducts the electricity well and an object with a  lower phase shift doesn’t conduct electricity well. Using the program in microprocessor control units, you can filter out objects above a certain level of phase shift, so that the metal detector doesn’t start beeping at the tiniest of objects.

Ground Balance

Most sands and soil contain some levels of iron in them. That is why the signal received from the ground itself can be stronger than the signal from items under the ground at modest depths. Of course, the phase shift caused by the ground itself remains consistent throughout. This is why metal detectors can have a constant output on the ground and exhibit changes when there is an object detected underground.

A metal detector that can keep a consistent reading for the ground is considered to be a ground balanced metal detector. Having good ground balance allows you to detect items underground with more accuracy.

Final Thoughts

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Understanding how VLF metal detectors work can help you use this tool in an efficient manner. The latest versions of VLF metal detectors are easier to use and more efficient than what they used to be a few decades ago and they will keep on improving. No matter how advanced they get, the basic principles of VLF metal detectors remains the same.

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