Latest Minelab Patent - 11th Feb 2016

[DOOLEY]

hello all..............

just thought i'd post a picture,

I simulated the TX of the fisher impulse a while back,

hopes this is a close representation dave.............

[Dave J.]

That looks about right, DOOLEY. The current waveform is alternating polarity triangles separated by off periods. The receiver gates on during the zero current periods. Searchcoil is mono, although I've done induction balance with similar transmitters.

[Teleno]

That looks about right, DOOLEY. The current waveform is alternating polarity triangles separated by off periods. The receiver gates on during the zero current periods. Searchcoil is mono, although I've done induction balance with similar transmitters.

First of all, congrats for your successful career doing things that you love to do.

One question... the triangular wave has a much slower decay than the usual high-voltage transient. How did you manage to get decent signal from small targets with such a sluggish decay? It's counterintuitive.

[DOOLEY]

ah,
coil current picture below...........



yes,
I was wondering the same,
thought FAST switch off would give a better target response ???

[Dave J.]

First of all, congrats for your successful career doing things that you love to do.

One question... the triangular wave has a much slower decay than the usual high-voltage transient. How did you manage to get decent signal from small targets with such a sluggish decay? It's counterintuitive.

Good question, there's a lot that the circuit does that's counterintuitive. But alas..... since I'm still on the payroll there's only so much I'm at liberty to divulge.
Part of the answer that's not counterintuitive, is the high rep rate. The emphasis on low conductors (our representative target was the U.S. 5 cent "nickel" coin) made the Impulse target response really muddy on high conductors like silver dollars.

[kt315]

Nearly all single-frequency metal detectors are sinusoidal. If you don't know what the MXT is, I know with absolute certainty it's sinusoidal because I designed the thing and it's still being manufactured that way, so why are you arguing with me about it? I usually expect smarter behavior on this forum.

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. Has nothing to do with half-bridge or full bridge, I've done both PI's and VLF's both ways, there's a full bridge switching nonresonant VLF sitting on my desk right now. I've been doing this stuff for a living for 35 years with successful products under a whole slew of different trademarks, it's not like I'm clueless.

If you don't want to believe me about anything, there are other folks here who also know their stuff, you can learn from them.

why you - in El paso - are not able to share schematic with me? you do bare words and no arguments from you only bare texts. i ask you SCHEMATICS AND O-SCOPE PICS.
I do not write that BBS is PI -!!!! i write IN YOUR LOGIC half- and full bridge driver is PI ie BBS IN YOUR LOGIC is also PI.

[clancy]

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.”
Example of “z=x+y.” Glider control flight “x” + independent engine fly plane but without controlled flight “y” both achieve before Wright brothers power control flight “z=x+y”, but from what you say Teleno, what Wright brothers achieve z=x+y be obvious. Don’t think many agree with you. (Some say “Everything is obvious in hindsight.”)
Same way, patent that solve problem “A+B” with solution “z”can be OK patent, depend on whether SOLUTION “z” obvious.
This patent much more complicate than TC spectrum from un-ground balance signals. E.g. response of 2 different un-ground balance frequency (w1,w2) as function of target TC have same value for only 1 single value of TC =not ambiguous, but e.g. in figure 3, trace 36 and 32 have same value for 3 very different TCs = ambiguous. This cause by ground balance nulls. Same with all other traces, all have same value as any other trace for at least 2 different TC value. Again ambigious. So, how to solve this with not ambiguous to TC spectrum? This e.g. be only part of problem need to solved “z”. For this patent solution “z NOT = x + y” where “x” = “ground balance signals” and “y” = “transform un-ground balance signal to TC spectrum,” because z need different more complicate than just use known prior art to transform ground balance signals to TC spectrum. Solution not obvious I think. Examiner think OK.

[6666]

The CZ operates in the frequency domain, not time domain like PI's. It's a type of induction balance VLF technology, operating at 2 frequencies simultaneously. Introduced in 1991 and still in production virtually unchanged.

The Fisher Impulse (no longer in production) was fully static (i.e. not "motion" or "autotune") and air tested on US coins out to about 10-12 inches (25-30 cm) as I recall. Sensitivity to low conductors was high enough that it did "see" salt water more than just a little bit, but of course a lot less than a regular VLF. No use for gold prospecting since it wasn't ground balanced. Like all PI's, it was rather vulnerable to electrical interference. Didn't like power lines at all. And in Los Banos we were able to detect some kind of U.S. Navy VLF transmitter somewhere up in the Suisin Bay area well over 100 miles (160 km) away (we RDF'ed it by triangulating from Santa Cruz) but holding the searchcoil plane horizontal nulled the H-field so it wasn't really a problem.

Thanks Dave its interesting reading about the development of such projects from so long ago.

[Dave J.]

why you - in El paso - are not able to share schematic with me? you do bare words and no arguments from you only bare texts. i ask you SCHEMATICS AND O-SCOPE PICS.
I do not write that BBS is PI -!!!! i write IN YOUR LOGIC half- and full bridge driver is PI ie BBS IN YOUR LOGIC is also PI.

The schematic of the MXT is White's IP, it is not mine to share. But by now you should know what a resonant single-frequency PNP-driven transmitter looks like.
BBS is not PI. Neither is the VLF sitting on my desk which has a similar transmitter. Neither is the CZ, which is single-ended switched drive.
If you don't want to learn from me, you're in luck because there are other people here who know what PI is, learn from them.

[Davor]

why you - in El paso - are not able to share schematic with me? you do bare words and no arguments from you only bare texts. i ask you SCHEMATICS AND O-SCOPE PICS.
I do not write that BBS is PI -!!!! i write IN YOUR LOGIC half- and full bridge driver is PI ie BBS IN YOUR LOGIC is also PI.

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]

BTW, GPZ7000 is a VLF as well

[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.

[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.

[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.]

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.