Corbyn Schematic

[FatBob]

I was doing some research and realized the Corbyn article didn't really have a full blown schematic with it.

So I drew one up. It has some cool features like bipolar TX, discrete preamp, top hat coil and other stuff.

Check out the 2 tones, one is for positive signals and one for negative. I might use that on my next project!

There are most likely mistakes (in the original and made by me) so do not build it if you don't want to mess
around a lot to get it going. I had to add lib a lot of the timing stuff (I hope I got it right!).

It's just for study and maybe to get some ideas!

Here it is;

[Qiaozhi]

I was doing some research and realized the Corbyn article didn't really have a full blown schematic with it.

So I drew one up. It has some cool features like bipolar TX, discrete preamp, top hat coil and other stuff.

Check out the 2 tones, one is for positive signals and one for negative. I might use that on my next project!

There are most likely mistakes (in the original and made by me) so do not build it if you don't want to mess
around a lot to get it going. I had to add lib a lot of the timing stuff (I hope I got it right!).

It's just for study and maybe to get some ideas!

Here it is;

[ATTACH]35315[/ATTACH]

This could be an interesting project.

According to the article, this detector was experimental, and originally developed for detecting gold in Western Australia (but so far unsuccessfully). Either he wasn't searching in the right place, or there's a basic problem we don't know about. As far as I know, there has never been any follow-up articles on this design.

Whatever ... it could still be a good learning exercise.

[kt315]

there has never been any follow-up articles on this design.
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http://www.geotech1.com/forums/showt...rl-Corbyn-s-PI

[6666]

What Candy said about Corbyn

In an article published in "Wireless World", May and June 1980, J. A. Corbyn describes a PI detector and an electronic circuit for that detector in which, in addition to discriminating against the ground eddy currents by not enabling the receiving means for some period immediately after the cessation of transmission, an attempt is made to discriminate against the remanent magnetization of the ferrite within the target volume induced by the transmitted magnetic pulse. Within the said article, as well as within some of its cited literature, the remanent magnetization of ferrite in the ground is credited to the effect called "magnetic viscosity".
In the circuit described by Corbyn, a transmitter coil transmits a magnetic field discontinuously, with alternating equal periods of transmission and non-transmission. Throughout the periods of transmission, the input of the receiver amplifier is grounded; amplification of received signals occurs between periods of transmission. There is also a delay after each transmission period in order to allow the eddy currents in the ground and the transmitting coil current to diminish to a level where they do not produce significant signal in the receiving means of the detector. The period during which the receiving amplifier is not grounded shall be called the analysing period.
Corbyn's circuit attempts to eliminate the effects of magnetic viscosity in the environment by electronically simulating that part of the signal which is due to the decay of the remanent magnetic field of the ferrite in the environment. Corbyn states that the magnetization, as a function of time, of ferrites in the environment is proportional to the magnetic susceptibility of the material, the change in the applied magnetic field H and a function g(t) which is a general function describing the form of the temporal evolution of the decaying magnetization. Corbyn further states that the function g(t) is independent of the magnetizing signal. The signal induced in the receiving coil of a detector will be proportional to the time derivative of g(t), which Corbyn claims is

g'(t)=(1-P)exp(-t/T₁)+Pexp(-t/T₂) (1) where P, T₁ and T₂ are constants which were determined empirically. This expression is largely based on measurements which were obtained using methods which are not disclosed in Corbyn's article.
The apparatus uses an electronic circuit to produce a signal with the characteristics of equation (1) and subtracts that signal, of a magnitude related to the magnitude of the received signal, from the received signal. The proposal of Corbyn is that any departure in the received signal from the form of the "magnetic viscosity" signal will produce a non-zero output from the subtracting amplifier, perhaps indicating the existence of eddy currents in the target volume. Corbyn states that the form of the temporal evolution of the magnetization of the ferrimagnetic material is independent of the magnetizing field applied. However, it can be shown that the temporal evolution of the magnetizing of the ferrimagnetic material does depend upon the applied magnetic field, knowledge of which is essential when trying to predict the form of the demagnetization of the remanent magnetism.
It is a well known phenomenon in the study of magnetism that ferromagnetic materials and ferrimagnetic materials will generally be left partially magnetized after being immersed in, then removed from, an applied magnetic field H. This remaining magnetism is the remanent magnetization or is sometimes referred to as the "historical component" of the magnetization, as opposed to the instantaneous component which is present only when an external magnetic field is applied. It is the source of the magnetic viscosity referred to by Corbyn.
Ferrites fall into the class of ferrimagnetic materials and are the single most important materials when discussing the magnetic background signals of ground in the context of metal detectors. In this invention it is not important to know anything about the instantaneous magnetic field produced by the applied field interacting with the ferrite during periods of transmission from the detector, as the receiving coil is disconnected from the sampling and processing means during periods of transmission and the reactive components of the ground signal respond instantly to changes in the transmitted field, as described previously. It is, however, important to understand what happens at a microscopic level to the structure of the ferrite both during and after the application of a magnetic field.
In order to simplify the discussion of these changes, some restrictions will be placed upon the parameters involved in the discussion. Begin with a piece of unmagnetized ferrite. The magnetic field applied to the ferrite has finite duration; at all other times there is no applied magnetic field.
A suitable model of the ferrite, in terms of its magnetic properties, is to think of it as composed of microscopically sized magnetized particles. The magnetic field attributed to each of these particles is spatially aligned in a way which is determined by some internal characteristic of that particle. The thermal energy supplied by the environment to each particle can induce changes in a particle which might produce a change in the spatial alignment of its magnetic moment. In unmagnetized ferrite, free of any applied magnetic fields, the change in the direction of alignment of the magnetic moment of any particular particle is essentially random when it occurs; a bulk sample of unmagnetized ferrite, in an environment free of fields and at biospherical temperatures, will remain unmagnetized.
When a magnetic field is applied to the bulk ferrite, the particles continue to change those characteristics which determine the directions of their magnetic moments at the same average rate. However, the direction to which those magnetic moments change is no longer entirely random; there is a tendency for the magnetic moment of each particle, when it changes, to have some component which is aligned with the applied magnetic field. Each such particle contributes to the net remanent magnetization of the bulk ferrite.

[6666]

Seems Corbyn applied for a patent and gives a bit more info.

http://www.delve.vub.ac.be/publicati.../GB2071327.pdf

[raygdunn]

Wow. They featured some serious projects in Wireless World back in 1980! Though I see it's successor Electronics World is "aimed at professional design engineers". Practical Electronics was more my level

http://www.geotech1.com/cgi-bin/page...rbyn/index.dat

The schema looks so much better as one sheet.


Ray

[Qiaozhi]

there has never been any follow-up articles on this design.
---
http://www.geotech1.com/forums/showt...rl-Corbyn-s-PI

Thanks KT315 - I've never seen that patent before.
Carl - this one needs adding to the Patents page on Geotech.