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One metal detector manufacturer claims that its new model provides ferromagnetic/nonferromagnetic information more than 60-70% from target detection depth- this for areas with an average level of mineralization, while for "normal" soils the discrimination reaches nearly 100% of the detection depth!!!
( It uses a DD type coil ) I am very skeptical about this. Target time constant information is true at depths up to 70-80% of the detection depth, but whether the target is ferromagnetic or not - experiments show that the limit is about 10 inches for a 10 inch diameter probe (the limit is equal to probe diameter). When working on pure magnetite sand, things drastically change in a tragic direction... Ferromagnetic targets distort the magnetic field in the near area of the probe. This only happens when the field changes its intensity, whether law the change is sinusoidal or linear. This field distortion can only be detected by an induction balance probe ( reactive component of the signal ) . The ability to detect field distortion decreases dramatically with increasing depth . Reason - the reactive components of the soil are many times stronger than those of deep targets . Experience shows that deep ferromagnetic targets are identified as non-ferromagnetic, and deep coins are unfortunately ``ironized''
- become iron
.Only with deep searching type detectors type TX-RX (operating frequency 6-15 Khz , sine wave ) deep iron targets can be registered by the divergence of the signal center ( The detector is in "all metals" mode - the receiving coil is at such an angle to the transmitting coil that the signal (residual voltage ) increases in amplitude for targets below the detector, and respectively - decreases in amplitude for targets above the detector) . When the operator passes over the deep target back and forth, the sound indication starts/ends asymmetrically on the ferromagnetic targets - the difference is about 3-4 inches . This is valid only for soils with low reactive signal components, of course... So - is it possible to identify deep ferromagnetic targets?
( It uses a DD type coil ) I am very skeptical about this. Target time constant information is true at depths up to 70-80% of the detection depth, but whether the target is ferromagnetic or not - experiments show that the limit is about 10 inches for a 10 inch diameter probe (the limit is equal to probe diameter). When working on pure magnetite sand, things drastically change in a tragic direction... Ferromagnetic targets distort the magnetic field in the near area of the probe. This only happens when the field changes its intensity, whether law the change is sinusoidal or linear. This field distortion can only be detected by an induction balance probe ( reactive component of the signal ) . The ability to detect field distortion decreases dramatically with increasing depth . Reason - the reactive components of the soil are many times stronger than those of deep targets . Experience shows that deep ferromagnetic targets are identified as non-ferromagnetic, and deep coins are unfortunately ``ironized''- become iron .Only with deep searching type detectors type TX-RX (operating frequency 6-15 Khz , sine wave ) deep iron targets can be registered by the divergence of the signal center ( The detector is in "all metals" mode - the receiving coil is at such an angle to the transmitting coil that the signal (residual voltage ) increases in amplitude for targets below the detector, and respectively - decreases in amplitude for targets above the detector) . When the operator passes over the deep target back and forth, the sound indication starts/ends asymmetrically on the ferromagnetic targets - the difference is about 3-4 inches . This is valid only for soils with low reactive signal components, of course... So - is it possible to identify deep ferromagnetic targets?
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