Early 1934 PI?

[Max]

Hi Geo, hi Max

No, don't have the complete article. Hope is not a complicated schematic because the article refers low weight, coil, battery, etc., but if the detector is a BFO type with tubes the weight is most heavy, don't know the principle, but almost sure the impulses are created by electromechanical vibrator or buzzer, operates 100-120 Hz.

I know there are many projects of enthusiast people in the world disperses in books and magazines, for example the detector published in Science & Invention in August 1921, with vibrator (called buzzer). Actuates as a rare type impulse with two coils.

As this, there are more and more. This is the reason I said: whe're reinventing the wheel and rediscovering the fire.

In the pic, the man has in the hand a pushbutton for to put in operation. The consumption in good adjustment point is near 2 A! And this is not balance/induction type, hope is two coils PI balanced by rheostat. The detector consist in:

2 exploring coils
Rheostat
Inductors
Transformer: 2 primaries, 1 secondary
Ammeter
Switch
Telephones (high Z)
Buzzer
Batteries
Pushbutton

No tubes, no heavy weight, etc.

Time by time this kind of publication I found on ebay or Abebooks.com

More temerary? Maybe near 1840 was discovered a detector like PI, but the investigator only refers the disturbance cause by metal near the coil.

Hi Esteban,
I think it is really interesting. For an historical point of view and not only.
I think the circuit works like a RUMKORF transformer using a vibrating switch to generate strong magnetic pulses (like in Marconi and Hertz experiments).
The vibrating switch open and close the circuit on TX stage...then something is used to reveal the induced (Lenz law) voltage variations on Rx stage.
It's not a RUMKORF with iron core and overlapped coils but with no core (would be the target) and distant coils (TX and RX) , or simply overlapped also but with no core.
What I don't understand is receiver section...telephone --> means some audio tone generation due to the coupling of TX and RX...but can't work like what we have (sampling, diff. integrators, etc) but most likely a beat frequency oscillator drived by some etherodyne style detector --> so seems
it have to not sample after delay but also "convert" rx signal in CW bfo style
detection.
So I guess it would be something between a real PI (modern type) and a BFO, but really don't know for sure.

Best regards,
Max

[Max]

Hello,

The "PI " concept is based on the delayed sampling (time domain technique) rather than shape of the waveform that excites the coil.

To my knowledge it was Claus Colani who invented, publicised and patented PI detectors:

• A new type of locating device, Archaeometry 1966,

• Method and Apparatus for Investigating a Generally homogeneous Medium, USA patent 3315155, 1967

and

• A novel metal detector using a pulse procedure for large areas with electronic object analysis and detection, Frequenz, 1968

The latter I have scanned. I can send to anyone interested, but it is in German !!



proscan

Hi,
I miss something in the previous post...
I've talked about TX only. Sorry.

I mean RX need to be coupled with TX section by this "pulses":

I think rumkorf transformer could be a good explaination of this.
When no target present ---> minimum coupling , so minimum signal in RX
When target present ---> maximum coupling , maximum signal (hi tension on secondary,
I think huge number of turns, coil).

But, can we call Pulse induction ? Don't know...there is a pulse train but too few
informations on RX stage. But is Rx put the "received pulses" in CW/BFO signal then
we end up also with a PI, just different kind of PI, with no integrators but a kind of
BFO output.

First RX stage components/schema could determine if it's a PI or not. If pulses are detected syncronously (time domain) there will be a chance that the detector could be considered a PI type, and I think it could be done by switching devices also.

Best regards,
Max

[Unregistered]

First PI

Hi All,

This subject has cropped up before, but true PI goes back to 1951 when J R Wait of Toronto University wrote a paper describing how a magnetic step function could be used to locate conductive objects. In 1955, Westcott, and then Johnson in 1956, wrote a theoretical paper entitled A Pulsed Bomb Locator. Practical experiments were also done, and decay curves plotted, but the current switching had to be done mechanically. Johnson was with the UK Army Signals Research and Development Establishment.

I have a magazine somewhere, called Junior Mechanics and Electricity, published in 1918, which describes a metal detector used in France after the 1st World War. This was attached to a plough to give farmers early warning of unexploded shells and bombs. This detector also was energised by a buzzer and may have qualified as an early PI. Depends whether the coil, or coils, were tuned or not.

Eric.

[Max]

Hi All,

This subject has cropped up before, but true PI goes back to 1951 when J R Wait of Toronto University wrote a paper describing how a magnetic step function could be used to locate conductive objects. In 1955, Westcott, and then Johnson in 1956, wrote a theoretical paper entitled A Pulsed Bomb Locator. Practical experiments were also done, and decay curves plotted, but the current switching had to be done mechanically. Johnson was with the UK Army Signals Research and Development Establishment.

I have a magazine somewhere, called Junior Mechanics and Electricity, published in 1918, which describes a metal detector used in France after the 1st World War. This was attached to a plough to give farmers early warning of unexploded shells and bombs. This detector also was energised by a buzzer and may have qualified as an early PI. Depends whether the coil, or coils, were tuned or not.

Eric.

Hi Eric,
I agree. Depends on what happens in RX stage. I think that if no tubes were present amplification must be realized through a normal transformer and a tuned circuit that then produced a signal , at audio frequencies, to be showed up by the hi-impedance "telephone" - could be a kind of hi-z headphone like in older radio-telegraph stations, much like one can find in older crystal radios circuits projects.
Seems like the TX and RX coupling is by target in the ground using eddy currents like in a rumkorf transformer and could do some detection ability.

"This subject has cropped up before, but true PI goes back to 1951 when J R Wait of Toronto University wrote a paper describing how a magnetic step function could be used to locate conductive objects."

I think that maybe someone discovered before 1900 that magnetic step functions can be used to find iron and other metals, due to the coupling they produce on such kind of circuits, but the first scientific paper and comprensive theory is from J R Wait work.

Best regards,
Max

[Max]

Hi all,
here is another similar apparatus:

1887Dr. J. H. Girdner devised an electrical bullet detector in human wounds

http://www.quincy.ca/tl_2004_firearms_tool_marks.cfm


Seems that can this detector can find a bullet in a human body at 10+ cm depth. Seems that worked at some hundred hertz by a vibrating switch controller circuit. Multi-coils Rx section - schematic unknown.
Unfortunately, I haven't more informations.

Best regards,
Max

[proscan]

If we talk about buzzers that energise TX coils, the earliest design I saw is in the USA patent:

• 1679339 Hidden Metal Detector.

As early as in 1881 Charles McEvoy patented metal (torpedo) detector in which "vibrating spring as in electric bells" is mentioned (not shown) as a source of A.C.
But those are not PI (time domain) detectors.

I am not sure which Wait’s paper Eric mentions:

• Transient electromagnetic propagation in a conducting medium

or (less likely)

• A conducting sphere in a time varying magnetic-field

Both 1951 and seem to be purely theoretical. What is more, transient effects were discussed long before (for instance "transients in conducting sphere" in Static and Dynamic Electricity by Smythe, 1939)

The bomb locator and the 1918 article sound very interesting. Eric, is there any chance go get a copy ?

thanks

Piotr, proscan

[Esteban]

Hi

This kind of terminology, time domain, sample, etc., doesn't exist at this time, but these pure electric metal detector can be considered as an early PI type.

In this circuit there are an electric balance between 2 coils and two small inductors attached to the trafo, called inductor balances, few turns.

If isn't BFO, PI, induction balance, ressonance-off, so, is electric balance-PI? or what? In wich place is?

Maybe Eric and others can use this principle for his PI!

The schematic:

[Max]

Hi

This kind of terminology, time domain, sample, etc., doesn't exist at this time, but these pure electric metal detector can be considered as an early PI type.

In this circuit there are an electric balance between 2 coils and two small inductors attached to the trafo, called inductor balances, few turns.

If isn't BFO, PI, induction balance, ressonance-off, so, is electric balance-PI? or what? In wich place is?

Maybe Eric and others can use this principle for his PI!

The schematic:

Hi Esteban,
- buzzer is actually a relay as I see in self-commutation mode (f osc. is determined by spring constant and magnetic field end other stuff)
- buzzer screw can vary operating frequency by some decade hertz
if too closed buzzer doesn't buzz...a short circuit and one cookes the coils
with 10-12 amperes
- rheostat/ammeter circuit used to limiting the operating current
- primarys are in opposition so a nulling "primary" voltage act in normal
conditions according to lenz law
- inductors are needed to nulling minor asymmetries in primary stage
- secondary drive directly the "thelephone" (hi-z earphone old style)

Seems a rumkorf like schema like I said, but with double primary in opposition and no core (air) --> would be the target near one of the coils.
When no target ---> minimum coupling ---> minimum signal
When target present ---> maximum coupling ---> imbalance of the nulling at
primary ---> signal at main freq. (audio range) in secondary and phone.

More coupling = more audio volume in the phone.

NO BFO. NO T/R. NO VLF. NO IB. NO PI.
Not a PI. Most like an induction balance. But no CW ---> so I'll call it "Rumkorf balanced style md" : "RBS".

I think many of early MD (say 1887 ahead) were based on this kind of RBS.

Best regards,
Max

[proscan]

I agree with what Max wrote just below. I also agree that Colani cooperated with Aitken who pioneered geophysical methods in archaeology. Correct me if I am wrong, but Eric also worked with Aitken back then (nonetheless he was a pioneer in this field, too).

But,

as far as CW detectors are concerned...

Some distinguish two types of detectors:

• Impulse detectors
• Continuos wave detectors (CW)

It is wrong !

For instance, Minelab Explorer or Whites DFX use pulse trains (which are definitely NOT continuos) but nobody would call it Pulse induction detectors, wouldn't he?

BBS/FBS detectors or Whites DFX are frequency domain detectors.



Piotr, proscan


PS
Have you seen Cobryn's PI British patent ? Good reading for those who knows his article in WW.

[Max]

I agree with what Max wrote just below. I also agree that Colani cooperated with Aitken who pioneered geophysical methods in archaeology. Correct me if I am wrong, but Eric also worked with Aitken back then (nonetheless he was a pioneer in this field, too).

But,

as far as CW detectors are concerned...

Some distinguish two types of detectors:

• Impulse detectors
• Continuos wave detectors (CW)

It is wrong !

For instance, Minelab Explorer or Whites DFX use pulse trains (which are definitely NOT continuos) but nobody would call it Pulse induction detectors, wouldn't he?

BBS/FBS detectors or Whites DFX are frequency domain detectors.



Piotr, proscan


PS
Have you seen Cobryn's PI British patent ? Good reading for those who knows his article in WW.

Hi Piotr,
yes it's true - only rx part indicate if it's a pi or not , I mean sampling at a fixed delay etc (time domain) not tx pulses alone. Right.

"Have you seen Cobryn's PI British patent ? "

No, not yet. I think I'll take a look soon.
Now I'm building the Bandido II (with some problems) and have little time to read much stuff. Also a lot of work to do.
Need lot of beers...



Best regards,
Max

[Esteban]

Hi

Are or not implicate frequency in PI detectors? If yes, also is a type of frequency domain. Is the pure electric metal detector in frequency domain? If the electromechanical vibrator close and open at X times for second, is in frequency domain. Works off-resonance type with oscillator? So, is in frequency domain. Works BFO in frequency? So, is in frequency domain. Induction/balance and two boxes type use frequency. Is or not in frequency domain? Are implicate time in frequencies? So, all are in time domain.

I know that pulse train detectors aren't PI.

Manufacturers tends to uses terminologies for to differentiate of others, BBS, bla, bla.

I think there are categories in managing the frequency.

* * * * * * * * *

so I'll call it "Rumkorf balanced style md" : "RBS".

I think many of early MD (say 1887 ahead) were based on this kind of RBS.

So there are two types:

- Electric (obsolete), who knows?

- Electronic

No sure if I'm wrong...

But, correct me if I'm wrong!

[Max]

Hi

Are or not implicate frequency in PI detectors? If yes, also is a type of frequency domain. Is the pure electric metal detector in frequency domain? If the electromechanical vibrator close and open at X times for second, is in frequency domain. Works off-resonance type with oscillator? So, is in frequency domain. Works BFO in frequency? So, is in frequency domain. Induction/balance and two boxes type use frequency. Is or not in frequency domain? Are implicate time in frequencies? So, all are in time domain.

I know that pulse train detectors aren't PI.

Manufacturers tends to uses terminologies for to differentiate of others, BBS, bla, bla.

I think there are categories in managing the frequency.

* * * * * * * * *

so I'll call it "Rumkorf balanced style md" : "RBS".

I think many of early MD (say 1887 ahead) were based on this kind of RBS.

So there are two types:

- Electric (obsolete), who knows?

- Electronic

No sure if I'm wrong...

But, correct me if I'm wrong!

Hi Esteban,
for me a real PI must have a direct control on the RX sample(s) , so we call this control to be "in time domain" , say at 10uS after the Tx pulse and seems that I called RBS detector haven't such a control.
It works on nulling voltages in the two symmetric primaries and that in continuity (no sampling here, no "time domain" control). It continuosly runs and when an imbalance occours then is revealed by the secondary voltage that become different from zero. There isn't a definite TX pulse (step function) and then a delay and then the sampling and so on...It's more like an induction balance but no sinusoidal wave here, just a series of spikes.

What I think about (maybe I'm wrong):

If we have no distinct separation between TX and RX phases we can't talk about PI or time domain analysis. When TX and RX are mixed at the same time we call this "frequency domain" (a maybe confusing terminology...)cause most of these freq. dom. detectors work on continuos wave , where tx and rx signals are always present at the same time and analysis is performed on frequency--> means continuos wave, so phase angles etc.
In so called "time domain" instead we have distinct, like in a radar, tx "time" and rx "time" and they are truly separated in time.

---
"
So there are two types:

- Electric (obsolete), who knows?

- Electronic
"

Yes, I think so. Electric means e.g. this kind of RBS or other similar, that seems very close to induction balance , due to the "balance" and the fact that coils must be aligned etc to "null" unwanted signals e.g. from ground.

Best regards,
Max

[Esteban]

Hi Max

Thanks for your comprehensive explanation.

Regards

Esteban

[Qiaozhi]

This is quite an interesting circuit. In fact, it is most similar to a P.I., as it transmits pulses and uses the same coil(s) to transmit and receive. However, unlike a normal P.I. with a monocoil, there are 2 TX coils that do not need to be balanced, so it's definitely not an I.B. system. At first glance it looks like there is no circuitry to sample the decay curve, but this is not true. If a metal target is located below one of the coils, then the decay time of this coil will be different to the other coil, and a signal will be heard in the telephone receiver. The transformer with 2 primary windings in opposition is used to cancel the signals from the two halves of the TX circuit. The meter is simply zeroed using the rheostat.

It could be quite interesting to build a 2 coil P.I. based on this concept, but obviously using more modern technology. It might even work quite well.

Esteban - how about this as a project?

[Esteban]

Don't know the performance. Article refers that is important to reduce in the minimum the vibrator sound, maybe in special receptacle. This was published on Science&Invention magazine, 1921.

But, as you said, can be re-adapted with modern components.

Do you want the article?