A
Anonymous
Guest
Ref: my post earlier today "DD LOOP DISCLOSURE (long)"
Suppose we have a round mono coil, and inside it, an induction balanced figure-8 coil.
The round coil is the transmitter. Also use it as the primary receiving coil.
The induction balanced figure-8 coil inside can be demodulated PI-fashion to extract position, depth, velocity, and shape parameter information, as described using (presumptively) double-D loops in my previous post.
It can also be demodulated like a VLF, extracting resistive and reactive components. The phases will be "normal" in one sweep direction, and "inverted" in the other sweep direction. This problem can be fixed by using the phase of a ground balanced signal (resistive) to synchronously rectify the reactive signal. This can be done to the static "DC" signal, or the signals can first be differentiated in order to improve rejection of DC offsets and of ground imbalance. The resulting reactive signal can then be used as an indication of the ferrous or nonferrous character of the target.
The system can be generalized to arbitrary target signal phase in order to implement discrimination/target ID of different types of nonferrous as well.
Because this is a far-field null system, it will not provide good results on deep targets under idealized conditions. However, in most soils, iron mineralization defeats accurate classification of deep targets anyhow. Nonetheless, this system has the following advantages:
1. Immunity to electrical interference, to which PI is particularly vulnerable. This will allow it to "air test" better than most alternative systems under conditions of high electrical interference.
2. Easy to build and to hold in a stable null.
3. First-order ground cancellation coming right out of the coil.
Bear in mind that these advantages do not pertain to the signals from the round mono coil which is also part of the loop assembly.
--Dave J.
Suppose we have a round mono coil, and inside it, an induction balanced figure-8 coil.
The round coil is the transmitter. Also use it as the primary receiving coil.
The induction balanced figure-8 coil inside can be demodulated PI-fashion to extract position, depth, velocity, and shape parameter information, as described using (presumptively) double-D loops in my previous post.
It can also be demodulated like a VLF, extracting resistive and reactive components. The phases will be "normal" in one sweep direction, and "inverted" in the other sweep direction. This problem can be fixed by using the phase of a ground balanced signal (resistive) to synchronously rectify the reactive signal. This can be done to the static "DC" signal, or the signals can first be differentiated in order to improve rejection of DC offsets and of ground imbalance. The resulting reactive signal can then be used as an indication of the ferrous or nonferrous character of the target.
The system can be generalized to arbitrary target signal phase in order to implement discrimination/target ID of different types of nonferrous as well.
Because this is a far-field null system, it will not provide good results on deep targets under idealized conditions. However, in most soils, iron mineralization defeats accurate classification of deep targets anyhow. Nonetheless, this system has the following advantages:
1. Immunity to electrical interference, to which PI is particularly vulnerable. This will allow it to "air test" better than most alternative systems under conditions of high electrical interference.
2. Easy to build and to hold in a stable null.
3. First-order ground cancellation coming right out of the coil.
Bear in mind that these advantages do not pertain to the signals from the round mono coil which is also part of the loop assembly.
--Dave J.