Latest Minelab Patent - 11th Feb 2016

[crane]

I'm glad you've said that, as several people seem to be under the impression that Minelab's BBS machines are PIs with discrimination. This erroneous idea seems to be prompted by some misleading marketing. Just because a metal detector has a non-sinusoidal (usually square wave) TX waveform, doesn't automatically means it's a PI.

Oops!
I replied to Dave's post after reading, and then found there was whole second page of replies on the same subject. Blimey ... this thread has become popular.

Well we have been here before in the GPZ7000 thread.

BBS/FBS and the GPZ process information in the time domain, same as PI.
BBS and FBS extracts X and three different bands of time constants, this is obviously different to VLF which processes info in the frequency domain.
BBS and FBS have a period where X can be extracted relatively free of the target signal, there is no such period in VLF.
The method of target excitation is similar to PI and quite noticeably different to VLF.

[Qiaozhi]

The Minelab circuit and waveforms and patents have been around for more than 20 years. The "BBS" etc. technology is not PI. It is sequential multifrequency.

I'm glad you've said that, as several people seem to be under the impression that Minelab's BBS machines are PIs with discrimination. This erroneous idea seems to be prompted by some misleading marketing. Just because a metal detector has a non-sinusoidal (usually square wave) TX waveform, doesn't automatically means it's a PI.

Oops!
I replied to Dave's post after reading, and then found there was whole second page of replies on the same subject. Blimey ... this thread has become popular.

[deemon]

Well, it is also PI because it demodulates the resistive component in the time domain during the periods of zero reactive voltage across the transmitter coil. New technique, some of us have known for a long time that it was theoretically possible, but to achieve zero reactive voltage across the transmitter coil close enough to perfect to make it worth the trouble, while current is flowing through the transmitter coil, is a tough engineering challenge and that's why it took so long for a company to actually achieve a marketable product with it.

By the way , the good method to distinguish PI machine from VLF is to observe a method of RX signal processing .... if our receiver analyzes only a fundamental frequency (f) of the TX pulse sequence ( or maybe 2 or 3 frequencies ) - this is a kind of VLF . But if we use simultaneously all the harmonic series of the coil current ( f , 2f , 3f , 4f , etc ) - we have a PI device .

[Davor]

Physics work the same for both.

look at fisher impulse driver and CZ-5 driver and find difference. while FIRST IS PI, SECOND IS VLF. yup, fisher impulse has voltage source connected to the coil, via capacitor. so you are ON MY SIDE NOW, Davor?

No. Actually you decided some time ago that my side is different from yours, but that's beside the point.
Ever heard of tri-state logic? It is achieved with the same half bridge you often mention, but with slightly different drive. Impulse uses it. There is no voltage source connected to the coil while receiving.
CZ transmits a pure square wave, plain and simple. A rail voltage is constantly there, either + or -, but always there. When polarity changes, the current forces itself through the coil back to the battery, and that's the reason it is efficient. But the real mojo is in Rx. It processes signal in frequency domain. It might as well process it in time domain, or combined. You have a lemon, and a few ways to squeeze it.

[Dave J.]

Davor, BBS works in same manner like Fisher Impulse, excluding 'bbs'.
BBS - full bridge driver, un-resonance coil
Fisher impulse - half bridge driver, un-resonance coil

so why first is VLF, but second is PI? monocoil in FI? - a PI can be also with RX coil. not argument.

FISHER IMPULSE IS NOT PULSE INDUCTION detector, but some people in MD industry actively PR some detectors as
PI. ADVERTIZING for dummy users.

The only thing that makes the Impulse transmitter different from conventional PI in terms of waveform, is that the flyback is of longer duration due to being clamped at a lower voltage. The receiver is off while current is flowing in the transmitter coil. It is not in any sense whatsoever a VLF.

And, you're mistaken about the resonance issue: there are patents on resonant transmitter PI's although to my knowledge none are marketed to the general public.

The distinctive feature of PI is intervals of zero reactive voltage across the transmitter coil (usually because there is no current flowing, the GPZ7000 is the exception), during which the receiver detects resistive phase voltages induced in the receiver coil (which may be the same coil, or may be IB or some other configuration). In the schematics forum of this website you can find many, many examples of both PI's and non-PI's, and US patents are available for free online (and I think also on this website?)

I have built PI's which also demodulated signals while there was current of changing amplitude flowing in the transmitter coil, which as a practical matter requires induction balance. I believe this was disclosed in my CZ/Impulse patent. I'm close to certain that the GPZ7000 also does this. This is a time domain VLF method. So a given machine can be both a VLF and a PI.

[kt315]

Mostly for the kind of processing that follows. All PIs have no voltage source connected to the coil after the Tx excitation, while all VLFs do.
The physics work the same for PI and VLF.

look at fisher impulse driver and CZ-5 driver and find difference. while FIRST IS PI, SECOND IS VLF. yup, fisher impulse has voltage source connected to the coil, via capacitor. so you are ON MY SIDE NOW, Davor?

[kt315]

Well, it is also PI because it demodulates the resistive component in the time domain during the periods of zero reactive voltage across the transmitter coil. New technique, some of us have known for a long time that it was theoretically possible, but to achieve zero reactive voltage across the transmitter coil close enough to perfect to make it worth the trouble, while current is flowing through the transmitter coil, is a tough engineering challenge and that's why it took so long for a company to actually achieve a marketable product with it.

without o-scope pics and schematics all your texts are only abstract discourse. chukcha ne pisatel', chukcha - chitatel', eah? =)

[Davor]

I often do some peer review of conference papers, and the vast majority of those do not need any improvement. Patents? Not so much.

[Teleno]

I liked it back when Strecker was the Examiner. He knew his stuff, and even if you thought you were in the clear, he'd usually shoot ya down. Blew about 90% of what I claimed into the weeds. No hard feelings, that was his job, and in the process I learned a lot.

I work as a patent examiner myself. Shooting down is the only fun of the job.

[Davor]

so why first is VLF, but second is PI? monocoil in FI? - a PI can be also with RX coil. not argument.

Mostly for the kind of processing that follows. All PIs have no voltage source connected to the coil after the Tx excitation, while all VLFs do.
The physics work the same for PI and VLF.

[Dave J.]

The quality of the US patent office is as good non existent, it's just rubber-stamps whatever is submitted to them.

I liked it back when Strecker was the Examiner. He knew his stuff, and even if you thought you were in the clear, he'd usually shoot ya down. Blew about 90% of what I claimed into the weeds. No hard feelings, that was his job, and in the process I learned a lot.

[kt315]

It is not. You confuse step voltage with PI.
There are basically 2 ways of conserving energy in VLF. One is running a resonant tank with an oscillator, a classic solution. Current recirculates between a coil and a capacitor.Another is running a step voltage source, or square wave if you like, and recuperating current once a coil goes to counter-phase. It may be counter-intuitive, but the square wave has many advantages over sine.
The most interesting one is complete avoidance of 1/f noise, typical for free-running oscillators. Maybe it does not sound as much, but it is in fact the final frontier of the current state of the art. The amplitude is always equal to rail voltage.
BBS is in fact an ingenious way of tailoring excitation with arbitrary frequencies - one at a time. Pick any - they do not have to be harmonically related. Now that BBS patents are all lapsed, it is a pity more people do not play with the concept. In CZ you filter frequency components of the fundamental and a harmonic. That's fine, but with BBS you don't have to do that, as you observe a single frequency at a time, change excitation frequency and observe another, and so forth. Simple.
But BBS is by all means VLF, same as CZ, regardless of square wave excitation.

Davor, BBS works in same manner like Fisher Impulse, excluding 'bbs'.
BBS - full bridge driver, un-resonance coil
Fisher impulse - half bridge driver, un-resonance coil

so why first is VLF, but second is PI? monocoil in FI? - a PI can be also with RX coil. not argument.

FISHER IMPULSE IS NOT PULSE INDUCTION detector, but some people in MD industry actively PR some detectors as
PI. ADVERTIZING for dummy users.

[Dave J.]

BTW, GPZ7000 is a VLF as well

Well, it is also PI because it demodulates the resistive component in the time domain during the periods of zero reactive voltage across the transmitter coil. New technique, some of us have known for a long time that it was theoretically possible, but to achieve zero reactive voltage across the transmitter coil close enough to perfect to make it worth the trouble, while current is flowing through the transmitter coil, is a tough engineering challenge and that's why it took so long for a company to actually achieve a marketable product with it.

[Teleno]

Just because “x” solution known for problem “A”, and “y”solution known for problem “B”, this not mean solution “z” obvious known for problem “A+B.”

Obviousness is a given because of these factors:

1. GB and discrimination are known features of metal detectors and their combination already exists in the prior art. Therefore such a combination, per se, is prima facie not inventive. You can't appeal to the combination alone to claim inventiveness.

2. As a consequence of (1), an unexpected, surprising synergistic effect should be present in the combination in order for it to be considered inventive. The effect must not predictable by the person skilled in the art when combining the known techniques disclosed in the patent. However, no such effect is present because GB and discrimination are completed separately and sequentially with no mutual interaction and doing exactly what the skilled person expects them to do, nothing more.

Contrary to what you pretend, there's no transformation of GB signals to TC spectrum. GB is treated first by a known method and completed, then TC by another known method starts. There's no interaction. This sequence is the normal procedure in previous combinations of GB + discrimination, therefore the combination is obvious.

Obviously the examiner didn't have the time to find the relevant prior art and do a meaningful substantial examination. The quality of the US patent office is as good non existent, they just rubber-stamp whatever is submitted to them.

[Davor]

BTW, GPZ7000 is a VLF as well