Coil resistance

[Sergey_P]

Hi, Carl-NC
Does the detector operate according to different physical laws?
The conductivity of ferrite is close to zero (infinite resistance), meaning there is no active component of the current. Consequently, there is no active component at the receiving end, and no voltage with phase = 0 is generated. Due to the inductive nature of the interaction with the target, the received signal is inverted, and the inductive nature of the ferrite and soil generates a negative voltage on the reactive component of the received signal (-90 for ferrite, -84...-87 for soil).
For a closed thin ring, there is no reactive component due to magnetization—only the active component of the flowing current with phase = 0 is present.

[Carl-NC]

We're saying the same thing, but the phase you get depends on whether you are looking at it in terms of magnetic field or induced voltage on the RX coil. That's what I was showing in post 14. There is always a 90° phase shift in the RX coil due to Faraday's Law.

[Sergey_P]

Hi, Carl-NC
In the Cartesian coordinate system, any reactivity has a phase shift of +90 or -90, and the active component has a phase shift of 0 or 180. Under no circumstances can reactivity become an active component, except in cases where this occurs in a person's false imagination.

[boilcoil]

...any reactivity has a phase shift of +90 or -90, and the active component has a phase shift of 0 or 180...

Hey Sergey, Karl isn't saying anything different. He's just showing you things from a different base of reference.

[Sergey_P]

Hey Sergey, Karl isn't saying anything different. He's just showing you things from a different base of reference.

At the very beginning, to simplify understanding, the concept of VDI is introduced, the phase at -90 degrees to the ferrite is taken as the initial reference point of 0 degrees, the Cartesian coordinate system is inverted and rotated, it is claimed that the ground signal is suppressed, not ignored, by rotating the phase coordinate system, that multi-frequency analysis of the pulsed signal is performed... and then they are surprised by the sounds of "hot rocks," tin cans, can rings, moving targets placed in the ground in an inaudible zone, and other unpleasant phenomena. Attempts to explain to people unfamiliar with the concepts of phase, impedance, Q factor, and so on, using fictitious or, worse, false physical principles of the process, lead to a degradation of knowledge about the surrounding world and a loss of communication between people.
As a rule, a psychiatrist himself is not so distant from his patients. I am not a doctor, I am an engineer, and I have no desire to treat search engine operators.

[Sergey_P]

About phases...
1. Real signals from a diamagnetic metal embedded in the ground, on a real device (not calibrated with ferrite), in a Cartesian coordinate system.
2. The same conditions, but with ground signal suppression (subtraction) in real time. Ignoring the ground signal by rotating the phase axes is useless here...

(Published about 15 years ago)

[Aziz]

... The conductivity of ferrite is close to zero (infinite resistance), ...

Hi Sergey,

this isn't really true. It varies between 100k .. x MegOhm depending on the ferrite type.
If you wind a coil to the plain ferrite core, the conductivity of the ferrite core may cause lots of parasitic capacitance to the coil windings. Many ferrite cores have an insulation layer (in reality a simple distance spacer) to lower these effects.

Even ferrite may cause very very little resistive response effects.
Magnetic viscous ferrites - or bad ferrites - (BH-curve has some area) does even have huge resistive response effects. The magnetic losses mimic resistive response.

Aziz

[Sergey_P]

Hi, Aziz
The dielectric loss tangent for ferrite is 10⁻³...10⁻⁴, which is more than enough to calibrate the device. (-90 degrees)
If you don't like ferrite, use a closed ring of thin wire. If you don't like wire, use carbon fiber (0 degrees).
Much more important is to determine the ground phase as accurately as possible, as this determines the detector's sensitivity to targets.

[Carl-NC]

I agree, the loss angle of ferrite is plenty close to zero to make it effective for calibration.

A closed ring of thin wire does not emulate ferrous ground, it emulates wet salt which is 90° from ferrous ground. Same with carbon fiber. If you use these to calibrate for ground by nulling the X signal, then you run the risk of error due to inaccuracy in the quadrature phase. The impact of all this depends on what you are trying to do: establish a fixed preset ground point, or calibrate the starting point for a variable GB, or something else. In short, better know what you are doing.