Pulse Induction History and Theory

[Aziz]

TO ADMINS
Carl and George,
Pulse induction metal detectors are designed, DIY and used in the 19th century and early 20th century, before the era of active electronic components. Several years ago, Esteban posted in the forum a circuit diagram, which seems consistent with the project shown here. However I can't find it in the forum.
Is this information deleted?

Hi Mike,

I think, you have posted this on AEGP Forum.
Aziz

[mikebg]

TO ADMINs

TO ADMINS
Carl and George,
Pulse induction metal detectors are designed, DIY and used in the 19th century and early 20th century, before the era of active electronic components. Several years ago, Esteban posted in the forum a circuit diagram, which seems consistent with the project shown here. However I can't find it in the forum.
Is this information deleted?

[Davor]

Something like ...
"no pain - no gain!"
(turn on a strong metal detector ... zzzzzt!
"no brain - no pain!"

[Prospector_Al]

Hi Eric,

How I got into the metal detector business is a funny story. When I find the old patent application, I'll send it to you and tell you what happened. My original career choice was medicine, and I was going through the premed program at UCLA, when something funny happened and completely diverted me to a different path...

In the mean time, I've been able to pulse 800 Amperes through an 8" coil. The voltages and currents are getting dangerous, so this may not have the potential for a commercial product. All kinds of safety precautions must be taken and the wiring must be able to take the high voltage...
On the other hand, some new, unexpected phenomena may become apparent. I'll keep one hand behind my back while I work and keep experimenting.

Allan

Hi Eric,

Thanks for the heads-up on the possible dangers of strong magnetics fields. In fact, there is a method known as "Transcranial Magnetic Stimulation", which is intended to affect brain activity.

This post may not belong here but rather in a thread that warns experimenters of the possible unintended consequences of strong Tx pulses...

Allan

[Prospector_Al]

Hi proscan,

Only a polyglot would want to see more posts in foreign languages, so you must be one. I am one too, but I think it would be a disservice to the majority of the members on this Forum to clutter up the pages with posts they don't understand.

Other polyglots, if there are any, may wish to comment...

Prospector_Al, alias Schatzsucher_Al, Cercatore_di_Tesori_Al, Chercheur_d'Or_Al, iskatel...

[Ferric Toes]

Hi Eric,

How I got into the metal detector business is a funny story. When I find the old patent application, I'll send it to you and tell you what happened. My original career choice was medicine, and I was going through the premed program at UCLA, when something funny happened and completely diverted me to a different path...

In the mean time, I've been able to pulse 800 Amperes through an 8" coil. The voltages and currents are getting dangerous, so this may not have the potential for a commercial product. All kinds of safety precautions must be taken and the wiring must be able to take the high voltage...
On the other hand, some new, unexpected phenomena may become apparent. I'll keep one hand behind my back while I work and keep experimenting.

Allan

Look out for unexpected phenomena in yourself as high level pulsed magnetic fields are thought to have physiological effects. When working on the pipeline detector, I found that I would get a headache and feel jittery if I was close to the coil for any length of time. This was a 20in square coil pulsed at 20A. I had a bright LED on the coil which fed off a stretched back emf pulse. This told me when the coil was active and working properly and also for the ROV operator who would use a TV camera to observe that the coils were operating correctly. When testing ROV electronics they would also hang a notice on the coil assembly for persons not to get closer than 1m.

Eric.

[Prospector_Al]

Hi Eric,

How I got into the metal detector business is a funny story. When I find the old patent application, I'll send it to you and tell you what happened. My original career choice was medicine, and I was going through the premed program at UCLA, when something funny happened and completely diverted me to a different path...

In the mean time, I've been able to pulse 800 Amperes through an 8" coil. The voltages and currents are getting dangerous, so this may not have the potential for a commercial product. All kinds of safety precautions must be taken and the wiring must be able to take the high voltage...
On the other hand, some new, unexpected phenomena may become apparent. I'll keep one hand behind my back while I work and keep experimenting.

Allan

[Ferric Toes]

Further Developments of the Pulsed Induction Metal Detector 1968.

Still in 1968. A paper I wrote for the Italian Journal "Prozpezioni Archeologiche Vol. 3".

Proz Arch001.pdf

[Ferric Toes]

Back to 1968. Here is a letter I received from F B Johnson who did the research for a Pulsed Bomb Locator in 1956.

Eric.

[Ferric Toes]

Hi Eric,

You are doing a great service to those of us interested in the history of the technology.
BTW, don't forget Barringer. Of course, I have a special reason for remembering him. In the early 1960s I designed a tramp metal detector which was an immediate success and I thought it would be easy to patent since there was nothing similar on the market in the U.S.
I was taken aback when the Patent Office rejected my claims on account of a certain Anthony Barringer in Canada having patented a pulsed device for detecting ore bodies. He used half a sine wave as a pulse and I used a square wave, but the technology was similar enough to cause a rejection. My company survived by licensing the technology from Barringer, but I was heartbroken.

I cashed in my chips and rode off into the sunset...

Barringer towed a "bird" after a plane. The bird contained the coil structure, far enough from the fuselage, to limit the magnitude of interference. Now, I have come full circle, becoming interested in larger targets which merit the use of a coil structure that's either on wheels or carried by two people. Such a big coil would have to be energized by an efficient switch, like a thyratron.

I think the modern thyratrons have such a low ON resistance that they don't get very hot...

All the best,

Allan

Hi Allan,

Yes, I have the Barringer information and a couple of his patents. I will put these into the history as well. Things here are not necessarily in date order as I have several boxes of papers that I sort through from time to time and when something relevant comes to light I will post it. Maybe when this is all finished it can somehow be put into a chronological order and maybe pinned. I have a patent which IMHO is pure PI, but dated 1942. It has a motor driven cam that operates contact breakers to to the TX and RX.
I had a personal visit at my home from Tony Barringer around 1970, suggesting I come under the wing of their patents. I somehow managed to convince him that what I was doing was sufficiently different and showed him the 1956 pulsed bomb locator paper, and heard nothing more.
As you have been in PI as long as I have, please feel free to contribute to the history. i.e.Tell how you got into PI and used it for industrial use. Your patent application and the grounds it was rejected.

Barringer also had a patent for a traffic control detector with the coil buried in the road. To get 1/2 sine pulses he simply transformed the 110V/240Vac down to a safer level and then 1/2 wave rectified it direct to the search coil. No line interference with that system! Now that was novel.

As regards using thyratrons, how will a practical coil cope with huge currents? Five years ago I did a design for a ROV mounted dual PI for offshore pipe location where I was pulsing 20A at 270pps through 500uH solid copper wire coils (1.7mm enamelled copper). The coil surface temperature reached 70C after about 1/2 hour. In practice, the coils would be kept cool when in the world best heat sink - the sea.

Eric.

[Prospector_Al]

Hi Eric,

You are doing a great service to those of us interested in the history of the technology.
BTW, don't forget Barringer. Of course, I have a special reason for remembering him. In the early 1960s I designed a tramp metal detector which was an immediate success and I thought it would be easy to patent since there was nothing similar on the market in the U.S.
I was taken aback when the Patent Office rejected my claims on account of a certain Anthony Barringer in Canada having patented a pulsed device for detecting ore bodies. He used half a sine wave as a pulse and I used a square wave, but the technology was similar enough to cause a rejection. My company survived by licensing the technology from Barringer, but I was heartbroken.

I cashed in my chips and rode off into the sunset...

Barringer towed a "bird" after a plane. The bird contained the coil structure, far enough from the fuselage, to limit the magnitude of interference. Now, I have come full circle, becoming interested in larger targets which merit the use of a coil structure that's either on wheels or carried by two people. Such a big coil would have to be energized by an efficient switch, like a thyratron.

I think the modern thyratrons have such a low ON resistance that they don't get very hot...

All the best,

Allan

[Davor]

There is a program called "Images2PDF" that comes with a freeware PDF Creator, and is very helpful in organising scans into a PDF file, such as this one:

[Ferric Toes]

Thanks Eric for sharing.

Since you skipped to the 1975, I am adding Colani's article from 1968. It is in German. I believe it is still interesting for all.

Actually, I would love to see more materials in German, Russian or other 'not-english' languages.

Yes, that is a very good paper and much of the object discrimination described, has not yet been achieved. I have an English version which I will post in due course. I jumped to 1975 as the thyratron/ thyristor/triac monster reared its head, but I will be back the the mid 1960's very soon as a huge amount of groundwork was done at that time.

Colani's work has been continued by Klaus Ebinger in Germany, who make PI mine and UXO detectors. www.ebinger.org

Eric.

[Prospector_Al]

Thyratrons

Thyratrons can be found on Ebay--I bought one for experimentation. Advantages: very low on resistance, can handle very high currents and can tolerate high voltage without breakdown, in contrast to semiconductor devices.

Prospector_Al

Hi Eric,

I have two EEV CX1622 thyratrons. 35 kV/5000 A. This is for the "Giant Nugget" detector, for Australian use.

You can have one ($600.00) if you wish--bought on Ebay--condition unknown at this time, but they look great.

Allan

[proscan]

Thanks Eric for sharing.

Since you skipped to the 1975, I am adding Colani's article from 1968. It is in German. I believe it is still interesting for all.

Actually, I would love to see more materials in German, Russian or other 'not-english' languages.

proscan