Reactance and Resistance

[Jackalope]

It is difficult to find info dealing with the dynamics behind MD operation - so I'll ask here where many smart people reside.

Looking at the impedance plane, pure XL has voltage 90 degree ahead of current, and XC has voltage 90 degrees behind the current. A vector in the first quadrant then represents the phase of +X/R and the fourth as -X/R. It should be true that the first quad is the component of RL and the fourth is RC, where these correspond to magnetic, lossless energy transformation and non-mag lossless energy transfer respectively.

So, in theory, the vector found in the first quad representing +X/R has components of R from the target and the soil. It also has positive inductance from the target and from the soil. It would also be assumed that the +X vector's amplitude is stronger (in this example) than any -X, otherwise the resultant would be in the fourth quadrant.

How is it that paramagnetic oxides in the soil, magnetite, or ironstone are related to inductive reactance with voltage leading current while non-ferrous metals are represented by a component of capacitive reactance (Xc) where voltage lags current?

I can't see the connection between the mutual induction between the Tx coil and Rx coil, and the affect that targets/soil have on it. If the VLF MD circuit differentiates between ferrous/non-ferrous by XC-XL, by what mechanism is capacitance present in the target or seen in the Rx coil phase as capacitance - or is it?

Wouldn't think a coin to have capacitance as seen by the fourth quadrant vector or a rusty bottle top to have inductive properties to produce a first quad vector.

If I can get the MD dynamics squared away I'll be able to sleep at night (kidding) - but I don't like mysteries.

Thanks for any explanations

[mikebg]

See thread "Targets frequency response"!

Hi John (jackalope),
Please, find below a thread "Targets frequency response" and read a Lesson1 attached at posting #8. There is an Exercise1 in posting #18, but its solution is given in postings after #105. There are answers to your questions in postings #86 and #88. If you have additional questions, please place them in that thread.

[WM6]

Hi John (jackalope),
Please, find below a thread "Targets frequency response" and read a Lesson1 attached at posting #8. There is an Exercise1 in posting #18, but its solution is given in postings after #105. There are answers to your questions in postings #86 and #88. If you have additional questions, please place them in that thread.

Hi mikebg,

maybe you answered yet, split in many post, on Jackalope questions here, but, please, do some effort and put your clear explanation here, cause it is about basic questions and worth to be clearly explained no matter of doubling some answer.

Thank you!

[mikebg]

Difference between mutual inductance and selfinductance

WM6, I would answer, but not in this thread because the questions of Jackalope are for frequency domain.
In 4th Sep 2009, Jackalope start a thread "Inductive coupling and sensitivity". Replies = 0. Why?
Then in september I suggested to the REMI group to write a response that contains a list of publications
- References, or where Jackalope to read about interested themes. They said that John should rediscover and advised me to translate in English an explanation "Difference between mutual
inductance and selfinductance in time domain and in frequency domain ". I really translate this
essay, but refuse to sent it in forum. Instead a spokesman of group designers of dead hobby, they turned me into a teacher of electricity to beginners. Then they predicted that
Jackalope will act as all other participants in the REMI group and will rediscover, reinvent, revise,
redesign and all "re-" for EMI sensor.
This is the second posting of Jackalope in forum and also contains questions. When I asked the group to answer,
they again forced me to send the explanation "Difference between mutual
inductance and selfinductance in time domain and in frequency domain ". I will fulfill their
desires to May, when my term as spokesman expires. At the risk of insult some participants
in this forum, that we think them as beginners, I'll give this explanation in thread "Targets frequency
response ".
Mike BG

[WM6]

WM6, I would answer, but not in this thread because the questions of Jackalope are for frequency domain.
In 4th Sep 2009, Jackalope start a thread "Inductive coupling and sensitivity". Replies = 0. Why?
Then in september I suggested to the REMI group to write a response that contains a list of publications
- References, or where Jackalope to read about interested themes. They said that John should rediscover and advised me to translate in English an explanation "Difference between mutual
inductance and selfinductance in time domain and in frequency domain ". I really translate this
essay, but refuse to sent it in forum. Instead a spokesman of group designers of dead hobby, they turned me into a teacher of electricity to beginners. Then they predicted that
Jackalope will act as all other participants in the REMI group and will rediscover, reinvent, revise,
redesign and all "re-" for EMI sensor.
This is the second posting of Jackalope in forum and also contains questions. When I asked the group to answer,
they again forced me to send the explanation "Difference between mutual
inductance and selfinductance in time domain and in frequency domain ". I will fulfill their
desires to May, when my term as spokesman expires. At the risk of insult some participants
in this forum, that we think them as beginners, I'll give this explanation in thread "Targets frequency
response ".
Mike BG

OK MIke, don't hesitate to post all themes and basic knowledge papers you have, no one should be insult. Thank you.

[Jackalope]

Sounds like the question is too basic - and yet the reply requires an inordinate amount of effort.

I suppose a long explanation on electronic theory would be welcome, but somehow I don't think that is what is needed here. I'm a meteorologist by trade not an electrical engineer, and I've read a lot of text on electronic theory, and even understood some of it, but there is nothing to tie the various concepts together.

There are pieces of information that I've gathered - the "whys" have centered around target reluctance creating a distorted pattern in the inductively coupled field, producing a Rx voltage. There is info on the ferromagnetic target with its higher permeability increasing flux, thereby increasing coil inductance and so decreasing freq of the tank circuit. I've read where the c-emf from eddy formation in a conductive target absorbs a portion of the Tx EMF and through target resistance the energy is dissipated as heat. All that leads to a sensed power loss to the Rx coil. Or again, c-emf from induced eddy currents in a metal target weakens the primary field over the target, decreasing total mag flux above, through, and below but increasing the flus away from the target, thus decreasing mutual inductance and increasing tank freq. Relating this and that to phase relationships in the Rx signal is unclear. So, how eddies produce an Xc/R type of component and ferro targets can produce XL/R positive inductance is not clear simply from the above explanation. Phase apparently is related directly to the ratio of lossless energy changes occurring at the target to its resistive energy loss, but why the polarities are necessarily leading/lagging - and how the mutual inductances play out from primary EMF to target and back to Rx coil. Lots of questions.

In any case, the reason I'm asking these basic questions about inductive and capacitive reactance in relation to resistance is that if I can crack that nut, many other concepts should fall into place.

In all honesty, I've looked at dozens of MD sites - there is little interest in electronic theory other than the MD goes "beep" on metal and "burp" on iron. Well, not quite that childish, but it is not a question that most seem willing to explore. I suppose it isn't necessary to know really, and based on the difficulty I've had trying to tie the concepts of operation together, I don't doubt most give up trying to figure it out.

I think these concepts can be explained rather simply. I know if you asked an atmospheric science question I wouldn't have to give an involved dissertation or resort to complex descriptions - even at its most advanced level the answer is just cause and effect, understandable to even those not entirely familiar with the wider subject. If it is logical anyone should be able to follow the reasoning.

[Carl-NC]

How is it that paramagnetic oxides in the soil, magnetite, or ironstone are related to inductive reactance with voltage leading current while non-ferrous metals are represented by a component of capacitive reactance (Xc) where voltage lags current?

There are 2 mechanisms in play. One is due to permeability (permeance), the other due to eddy currents. Let's look at them in terms of magnetic fields.

The TX coil transmits an alternating magnetic field. We'll say this one has a phase of 0 degrees, i.e., our reference phase.

A perfect ferrite does not support eddy currents, but does "focus" the transmitted magnetic field because of permeance, causing it to become distorted. This distortion upsets the induction balance and the RX coils "sees" a signal. But the distortion is entirely in-phase with the TX field, so the RX coil sees an effective target field that is at 0 degrees.

With a non-ferrous metal target, the TX field induces eddy currents which produce a counter-magnetic field at the target's surface. In an ideal super-conductor, the counter-magnetic field is exactly equal to the incident field, but 180-degrees out-of-phase. So the RX coil sees an effective target field that is at 180 degrees.

Real targets are everywhere in between. The magnetic phase of practical ferrite usually comes in around 2-3 degrees, and average ferric ground does as well. The magnetic phase of real non-ferrous metal targets depends on the conductivity of the metal and the thickness, as they combine into a skin effect, which dominates the actual phase of the eddy response. Thinner and/or less conductive targets have a magnetic phase that progresses from 180 down to 90 degrees.

Ferrous targets combine the permeance response with the eddy response to give an overall phase from 0 to 180 degrees. If permeance dominates (as with an average nail) then the target phase is between 0 and 90. If eddies dominate ("big iron"), the target phase is between 90 and 180.

But wait, there's more...

Non-ideal ferric ground can slowly shift the TX phase with depth, and further shift the target phase on the way back up, causing a target phase error that depends on depth. Explaining why some non-ferrous targets can creep past 90 degrees, and why TID is unreliable on deep targets.

Also, most phase TIDs are based on the voltages inside the detector, and there are 2 additional phase shifts: a 90-degree shift on the TX, and another 90 on the RX. So most consider non-ferrous targets to be in quadrant 1 (0-90), and ferrous to be in quadrant 2 (90-180). On top of that, companies assign VDI numbers that seem to be random. White's uses -95 for ferrite to +95 for ideal non-ferrous.

As you can see, the question is very basic to the concept of how a detector works, but does require a rather lengthy response.

- Carl