Latest Minelab Patent - 11th Feb 2016

[Dave J.]

But at least Dave's patent is actually readable.

Dave - How good was your prototype at rejecting iron?

Also, I must thank KT315, whose comments prompted me to read it thoroughly in the first place.

The prototype that got buried forever did iron rejection the same way a VLF/TR does, fully (except for gating) static using the reactive signal. So it wasn't very good at rejecting iron; or perhaps better said too enthusiastic about using ground minerals to reject good targets.

An earlier version of the technology was a very simple lightweight no target ID fully static unit, ground balanced in the customary PI style to knock out the "red stuff". The timing put the "target response hole" right about zinc pennies, and iron fell below that. So you could hunt for high conductivity coins and dig no trash other than the occasional beverage can, which needn't be dug anyhow because when you lift the searchcoil the signal doesn't quickly disappear. For US coinshooting in bad ground, the best metal detector I've ever swung. It was just technology development, not a prototype of a product, and wouldn't have been salable anyhow because in discrimination mode it was only good for about 5, maybe 6 inches. In all metals (not ground balanced) more like 8 inches.

[Qiaozhi]

Actually not.
Because i do avoid to read patents!

But at least Dave's patent is actually readable.

Dave - How good was your prototype at rejecting iron?

Also, I must thank KT315, whose comments prompted me to read it thoroughly in the first place.

[ivconic]

I can understand ....
...
Confused?
You should be.

Actually not.
Because i do avoid to read patents!

[Davor]

I think KT315 is just pulling some legs here.

[Qiaozhi]

I can understand KT315's confusion here, as Patent 4868504 does blur the lines somewhat between Pulse Induction (PI) and Continuous Wave (CW) detectors. There is also the language translation problems.

Analysis of Patent 4868504:

The circuit shown in Fig.2 is used to generate a non-sinusoidal transmit voltage. It energizes the transmit coil and returns energy to the power supply from the collapse of the magnetic field, thus minimizing power consumption.

There is a description of the two main types of metal detector: Very Low Frequency (VLF) induction balance detectors, and Pulse Induction (PI). However, this is where a lot of confusion is generated, since several of the embodiments in the patent incorporate an induction balanced coil, and at least one embodiment is referred to as CW.

PI detectors are described as typically including an oscillator which applies brief pulses at a rate of 100 to 3000 pps to a search coil having a single winding. [Of course, this could also be an IB type.]
Eddy currents that are induced in nearby metal objects during the transmit pulse will continue to flow for a period of time after the transmit pulse is terminated, and the receiver detects the voltage that is induced by the decaying eddy current. [So … what distinguishes a PI from other detectors is that the received signal is sampled during periods when the transmitter is turned off, and there are no TX oscillations during the receive period. As an example, the TR detector in ITMD has a transmit circuit that generates pulses which are applied to a search coil. The coil is tuned by a parallel capacitor to generate a decaying sine wave signal during the time when the TX pulse is off. Hence, it is not a PI, even though it uses a pulsed transmitter.]

The purposes of the invention are:

1. To provide a new and improved apparatus and method for metal detection and geophysical exploration that overcomes the limitations of PI and VLF technologies.
2. To minimize power drain on the battery.

In the circuit (Fig.2) the search coil is energized to produce a magnetic field which builds up and collapses. [This is one of the requirements for it be a PI.]

There are two main disclosed embodiments:

1. The first uses separate TX and RX windings in IB, and are monitored continuously.
2. The second uses temporally separated pulses in IB, and monitored only during time intervals of inactivity between the pulses.

In operation, current is alternatively exchanged between capacitors 23 and 24, and energy lost is topped up by the battery.

Sync demods operate on the fundamental and 3rd harmonic of the RX signal (due to the driven node being stimulated by a square wave) as follows:

1. Fundamental resistive signal - 1/3rd of the 3rd harmonic resistive signal = composite resistive signal. (ignores salt water and soil conductivity).
2. 3rd harmonic reactive signal - fundamental reactive signal = composite reactive signal (ignores magnetite in the soil).
3. Composite reactive / composite resistive = character of metal target.

Other combinations are also discussed.

Fig.5 shows an embodiment employed in a PI detector, which exhibits a greatly reduced power drain on the battery. This embodiment is capable of using a mono coil, although an IB coil is recommended. Clearly this version is a PI, as (referring to Fig.6) the metal target detection occurs during periods 3,4 and 7,8 when the transmit signal is off. Both salt and magnetite are eliminated in this instance by the simple process of not sampling early in the decay period, so obviously this method cannot be used for finding low conductivity targets such as thin gold chains or small gold nuggets.

By using an IB coil, it would be possible to monitor the RX coil continuously and combine the advantages of both CW and PI detectors, together with minimal battery drain. [Note that the transmitter coil is non-resonant.]

The patent appears to be a disclosure of Dave's discriminating PI, with only one particular embodiment being of relevance to the Fisher Impulse. The Fisher Impulse is definitely a PI, whereas any variant employing the concept displayed in Fig.4 would appear to be a combination of both PI and CW technologies. As I said at the start, the patent blurs the two techniques in certain embodiments. Even with Fig.4 there is still a pulse that turns off, thus creating a non-resonant decay curve. However, due to the CW nature of the waveform, it is possible to extract both resistive and reactive components from the RX signal (an IB coil is required to make this work) and hence provide target ID. Although you may find it difficult to understand it, even Fig.4 is still essentially a PI. You must take into account the fact that the current lags the voltage in the transmit coil, so that part of the period is effectively inactive, and during this time energy is returned to the capacitors 23 and 24.

Confused?
You should be.

[ivconic]

"...and to put some more petrol on the fire..."

Indeed Dooley!

[DOOLEY]

pictures taken direct from FISHER IMPULSE PAT.........

FIGURE : 6
TRANSMIT WAVEFORM OF IMPULSE :


FIGURE : 4
showing how it "COULD" be used for CW TX :



I learnt how to READ from an early age,
posting pictures for clarity...............

that,
and to put some more petrol on the fire.............
as it seemed to be going out.................
LOL.

[ivconic]

still one serb here!

One visible and 10 000 invisible... beware!
...
You can call me an ignorant and teach me the tech... but maaannn you are trying to do that with Dave J. !!!???
Who's next? Eric?
Duuuude!

[Teleno]

still one serb here!

There's nothing in the world more pathetic than the quibble of two d*ckheads on the internet.

[ivconic]

And kt315 just proved it, and at the same time proved that BBS is PI-- see his post right above yours?

But he's wrong: everyone knows that VLF's run off regulated supplies whereas PI's run straight off a lead-acid battery. Has nothing to do with how signals are created or processed or how metals are detected, the "pulse" is what happens when you connect the circuit to the battery without the current limiting you expect from a power supply regulator.

That's what i am talking about, man!
Recently we the Europeans expelled ML from EU territory just because of similar behavior!
Now with huge help of KT's unbeatable evidences&proofs, you, the Americans, can successfully do the same!
...
You owe a certain sum of money to KT... he finally opened your eyes man!
Admit!!!

[kt315]

Is it a goose or a gander? What's the point you're trying to make?

Here, help yourself: Как перестать спорить с людьми в жизни и в интернете — 11 методов

[kt315]

Is it a goose or a gander? What's the point you're trying to make?

Here, help yourself: Как перестать спорить с людьми в жизни и в интернете — 11 методов

still one serb here!

[Dave J.]

It is obvious that thieves from ML stole whole concept from early Fisher designs....

And kt315 just proved it, and at the same time proved that BBS is PI-- see his post right above yours?

But he's wrong: everyone knows that VLF's run off regulated supplies whereas PI's run straight off a lead-acid battery. Has nothing to do with how signals are created or processed or how metals are detected, the "pulse" is what happens when you connect the circuit to the battery without the current limiting you expect from a power supply regulator.

[Teleno]

ok, i do it. http://www.slideshare.net/seriousdet...st-manual-scan

A BBS detector transmits a complex multi—period sequence of pulses which yields a host of information, about the object and the ground which is not available in any otherdetector.

PULSES -! Dave, agree that BBS is pulse induction in its nature ))))) but yup, you was the pioneer who patented half bridge transmitter like a "PI".

Is it a goose or a gander? What's the point you're trying to make?

Here, help yourself: Как перестать спорить с людьми в жизни и в интернете — 11 методов

[ivconic]

It is obvious that thieves from ML stole whole concept from early Fisher designs....