Finding Nuggets With a Metal Detector
Part 1 - how they work
VLF and PI Detectors how they work
VLF - Very low frequency
VLF - Produces a relatively low power continuous sine wave into the transmit coil. It analyze a signal received with a separate receive coil winding. The signal from an object will increase the amplitude of the receive signal. But it will also shift the receive signal with respect to the transmit signal. That way an object can be analyzed by not only the intensity or amplitude increase of the signal, but by just how much the signal has shifted. Most VLF operate at a single frequency.
PI - Pulse induction
PI's operate on the principle of generating a large current pulse in the coil and then analyzing the signal in the coil a short time after the pulse is turned off. This cycle is repeated on a continual basis. When the current is flowing in the coil, a magnetic field is generated that expands from the coil. When this field encounters a metallic object such as a gold nugget, current begins to flow in the nugget as the result of this magnetic field. When the current suddenly stops in the coil, the coil field collapses which in turn causes the current in the object to collapse. This secondary collapse of current in the nugget causes it to produce its own field that now generates back to the coil. This target signal ultimately adds to the collapsing coil signal, thus making the coil signal change very slightly. Pulse Induction metal detectors are specialized instruments. They are generally not suitable for coin hunting urban areas because they do not have the ability to identify or reject very small ferrous (iron) trash.
The pros and cons of each
VLF - Pros
Their ability to detect small gold is somewhat superior to the PI detectors. Most VLF gold detectors can pick up surprisingly small nuggets in the hands of an experienced operator. The cost of most new VLF detectors is well under $1000, and sometimes you can even pick up a good used unit for a few hundred dollars. Weight can quite a bit less. Battery usage is much less. They work well if there is no ground - tailing piles of mostly large rocks.
VLF - Cons
They don't detect as deep as the PI. They are unable to handle some highly mineralized ground. Hot rocks can be a problem.
PI - Pros
They are intended for maximum depth under extreme search conditions such as salt-water beaches and highly mineralized ground. In such conditions PI type detectors produce superior results when compared to VLF models, particularly in the ability to ignore such extreme ground and penetrate it for maximum depth. They can be used for relic hunting rural areas where iron trash is not present in large quantities, or is desire.
PI - Cons
Cost - they can be as low as $1200 or as high as $6000. Weight - they take a lot of power to run, means lots of batteries. Some times they can go too deep - I have dug down 12 to 15 inches to find a 1/2 inch long square nail.
VLF - Very low frequency
VLF - Produces a relatively low power continuous sine wave into the transmit coil. It analyze a signal received with a separate receive coil winding. The signal from an object will increase the amplitude of the receive signal. But it will also shift the receive signal with respect to the transmit signal. That way an object can be analyzed by not only the intensity or amplitude increase of the signal, but by just how much the signal has shifted. Most VLF operate at a single frequency.
PI - Pulse induction
PI's operate on the principle of generating a large current pulse in the coil and then analyzing the signal in the coil a short time after the pulse is turned off. This cycle is repeated on a continual basis. When the current is flowing in the coil, a magnetic field is generated that expands from the coil. When this field encounters a metallic object such as a gold nugget, current begins to flow in the nugget as the result of this magnetic field. When the current suddenly stops in the coil, the coil field collapses which in turn causes the current in the object to collapse. This secondary collapse of current in the nugget causes it to produce its own field that now generates back to the coil. This target signal ultimately adds to the collapsing coil signal, thus making the coil signal change very slightly. Pulse Induction metal detectors are specialized instruments. They are generally not suitable for coin hunting urban areas because they do not have the ability to identify or reject very small ferrous (iron) trash.
The pros and cons of each
VLF - Pros
Their ability to detect small gold is somewhat superior to the PI detectors. Most VLF gold detectors can pick up surprisingly small nuggets in the hands of an experienced operator. The cost of most new VLF detectors is well under $1000, and sometimes you can even pick up a good used unit for a few hundred dollars. Weight can quite a bit less. Battery usage is much less. They work well if there is no ground - tailing piles of mostly large rocks.
VLF - Cons
They don't detect as deep as the PI. They are unable to handle some highly mineralized ground. Hot rocks can be a problem.
PI - Pros
They are intended for maximum depth under extreme search conditions such as salt-water beaches and highly mineralized ground. In such conditions PI type detectors produce superior results when compared to VLF models, particularly in the ability to ignore such extreme ground and penetrate it for maximum depth. They can be used for relic hunting rural areas where iron trash is not present in large quantities, or is desire.
PI - Cons
Cost - they can be as low as $1200 or as high as $6000. Weight - they take a lot of power to run, means lots of batteries. Some times they can go too deep - I have dug down 12 to 15 inches to find a 1/2 inch long square nail.
|
|