Triangular Wave Technology

[Tinkerer]

OK I'm not exactly sure whats clear but I'll have a stab. What I see in your sim is that the difference between the TX on sample and peak fly-back response sample is the same either way. However you have a lot less time to sample the peak with the shorter on pulse so I guess that means a crapper SNR. But then of course you can pulse more frequently and probably make it back. Hmm yes.. not super clear... not to me anyway.

[ATTACH]22851[/ATTACH]
Midas

Thank you for the feedback. I keep making the same mistake, thinking what is clear to me, is also clear to others.

What you correctly point out, is that the step response is the same for both TX. We can also see that the coil current is equal for both TX.

At the point of the first sample of a traditional PI, soon after TX switch OFF, however, the target signal (pink) amplitude of the short (50us) TX pulse, is very low, while the target signal (red) amplitude is much higher.

With the short TX, the TX ON eddy currents are of high amplitude. The step function inverts the coil current. the TX eddy currents are being nulled by the new eddy currents that are of opposite polarity.

The end effect, is that the measurable signal amplitude soon after TX OFF, is very low.

[mikebg]

SINE INDUCTION METAL DETECTOR

What next?
Can you tell which form of TX current is most inappropriate for the WB metal detector?

HINT: It looks very much like a triangle wave and in radio ingeneering is called CW (continous wave).

SINE INDUCTION
Below is attached the answer.
Despite time domain is not used in my hobby, I see how a synchronous demodulator (in a VLF metal detector) samples this waveform in T/2 windows.
The next question is:
How to distort the sine waveform in order to obtain frequency spectrum like trapezoidal waveform?
HINT: See figures of patent mentioned in post #54.

[Tinkerer]

Going back to the triangular Tx wave form.
There is a big difference in response between a perfectly symmetrical triangular wave form and a triangle that is more like a saw-tooth.

With an asymmetrical triangle, we might have a long ramp up, say 300us and then a short ramp down, say 10us, for a proportion of 30 to one.

We have then 2 very distinct Tau's. The long ramp is good for exciting targets with a long TC and the short ramp is good for short target TC's.

[Davor]

Whatever the length of the ramp, it will always relate to the applied voltage as e=di/dt
With e=const, the targets will never make any distinction between the two. Longer period would enable you to sample for a longer period, but I see no other relationship with the targets' tau.

[Prospector_Al]

Hi Eric,

You are very observant! And very sharp, putting two and two together. I also saw a logo with similar shapes somewhere, and I didn't think that anybody would decipher the meaning of the logo. I'm sure that in due time, the meaning will be made clear...

I'm truly amazed to see how many permutations are possible, like variations on a theme in music...The basic theory of metal detectors seems to be simple, yet it's very complex, and even those who have been investigating the various phenomena involved for a long time, suddenly make new discoveries. This appears to be possible only when one is bold enough to disregard the opinions of those who know it all...

The history of metal detectors has been outlined on theses pages, and it's fair to ask, "Why is it that "the perfect metal detector" has not yet been designed?" Is it because of immense difficulties or stubborn adherence to incorrecy ideas? The history of medicine is replete with similar problems--the faulty perceptions of Galenius percepted for over 500 years...

May The Force be with You,

Allan

[Aziz]

Hi Eric,

You are very observant! And very sharp, putting two and two together. I also saw a logo with similar shapes somewhere, and I didn't think that anybody would decipher the meaning of the logo. I'm sure that in due time, the meaning will be made clear...

I'm truly amazed to see how many permutations are possible, like variations on a theme in music...The basic theory of metal detectors seems to be simple, yet it's very complex, and even those who have been investigating the various phenomena involved for a long time, suddenly make new discoveries. This appears to be possible only when one is bold enough to disregard the opinions of those who know it all...

The history of metal detectors has been outlined on theses pages, and it's fair to ask, "Why is it that "the perfect metal detector" has not yet been designed?" Is it because of immense difficulties or stubborn adherence to incorrecy ideas? The history of medicine is replete with similar problems--the faulty perceptions of Galenius percepted for over 500 years...

May The Force be with You,

Allan

Hi Allan,

do we see the "Giant Nugget Detector" soon?
You know, the gold prospectors want it. They are fed up with flysh.. nuggets and chasing them with a magnifier.


Cheers,
Aziz

[Prospector_Al]

Hi Aziz,

My Crystal Ball indicates that the "G.N.D." will emerge some time this summer. I'm renewing my expired passport so I can fly to Ankara to conclude the deal.

Frodo lives,

Allan

[Prospector_Al]

Going back to the triangular Tx wave form.
There is a big difference in response between a perfectly symmetrical triangular wave form and a triangle that is more like a saw-tooth.

With an asymmetrical triangle, we might have a long ramp up, say 300us and then a short ramp down, say 10us, for a proportion of 30 to one.

We have then 2 very distinct Tau's. The long ramp is good for exciting targets with a long TC and the short ramp is good for short target TC's.

Hi Tony,

I believe such a detector already exists--I just can't remember where I saw it...

Allan

[Aziz]

Hi Aziz,

My Crystal Ball indicates that the "G.N.D." will emerge some time this summer. I'm renewing my expired passport so I can fly to Ankara to conclude the deal.

Frodo lives,

Allan

"G.N.D." sounds so good. I'm so familiar with the acronym.

How about the VTEM-Technology? (Vaporize The Evil Monopolist Technology)

Aziz

[Ferric Toes]

"G.N.D." sounds so good. I'm so familiar with the acronym.

How about the VTEM-Technology? (Vaporize The Evil Monopolist Technology)

Aziz

Not good for two reasons. 1) It will get confused with VETEM (Very Early Time ElectroMagnetics). 2) Better to keep such posts for Doug's Forum as it supports his agenda.

Eric.

[Aziz]

Not good for two reasons. 1) It will get confused with VETEM (Very Early Time ElectroMagnetics). 2) Better to keep such posts for Doug's Forum as it supports his agenda.

Eric.

Well Eric, actually the VTEM is a real technology (The Vapour TEM(c)(r)(tm)) . But it has the same effect of vapourizing the evil monopolist (there is an obvious "majik" harmony link here).
Aziz

[Ferric Toes]

Well Eric, actually the VTEM is a real technology (The Vapour TEM(c)(r)(tm)) . But it has the same effect of vapourizing the evil monopolist (there is an obvious "majik" harmony link here).
Aziz

OK, VTEM is real ( Versatile Time Domain Electromagnetics); helicopter borne, 230A peak TX, 4mS pulse width, bipolar standard technology. VETEM (Very Early Time EM) is real, down to 1uS TX pulses, just a few Amps, very small sample delay. Vapour TEM is unreal as it's name suggests. There is also UTEM, ZTEM and possibly others. I would prefer not to spread things too far as we already have enough coil configurations, pulse shapes, differential arrangements, ground balance, S/N, analogue, DSP, etc, etc. to keep us occupied for years.

Eric.

[Aziz]

OK, VTEM is real ( Versatile Time Domain Electromagnetics); helicopter borne, 230A peak TX, 4mS pulse width, bipolar standard technology. VETEM (Very Early Time EM) is real, down to 1uS TX pulses, just a few Amps, very small sample delay. Vapour TEM is unreal as it's name suggests. There is also UTEM, ZTEM and possibly others. I would prefer not to spread things too far as we already have enough coil configurations, pulse shapes, differential arrangements, ground balance, S/N, analogue, DSP, etc, etc. to keep us occupied for years.

Eric.

Yep, I have found, that the term VTEM is in use (see http://www.geotech.ca/vtem).


Anyway. Back to triangular wave technology.

I have compared a standard PI, triangular current wave (50% duty cycle, symmetrical triangle), the TEM (we use it here) and an unknown new configuration (named X) regards to target response of a large TC target (1 ms).

PI: almost zilch (averaged integrated response 208 nV just to give a figure for a comparison here)
Triangular: better (averaged integrated response 6 µV)
TEM: much better (averaged integrated response 22 µV)
X: best (averaged integrated response 92 µV)

The TEM isn't that bad for the giant nuggets regards to its simplicity and power efficiency.

Cheers,
Aziz

[Carl-NC]

I have compared a standard PI, triangular current wave (50% duty cycle, symmetrical triangle), the TEM (we use it here) and an unknown new configuration (named X) regards to target response of a large TC target (1 ms).

PI: almost zilch (averaged integrated response 208 nV just to give a figure for a comparison here)
Triangular: better (averaged integrated response 6 µV)
TEM: much better (averaged integrated response 22 µV)
X: best (averaged integrated response 92 µV)

Heaping gobs of information missing here.

[Ferric Toes]

Yep, I have found, that the term VTEM is in use (see http://www.geotech.ca/vtem).


Anyway. Back to triangular wave technology.

I have compared a standard PI, triangular current wave (50% duty cycle, symmetrical triangle), the TEM (we use it here) and an unknown new configuration (named X) regards to target response of a large TC target (1 ms).

PI: almost zilch (averaged integrated response 208 nV just to give a figure for a comparison here)

Yes, I am interested in further details and how you arrived at a zilch figure. i.e. coil type, coil diameter, coil inductance, peak current, TX width, sample delay, sample width, type of GB (or not), integration time, surface area of target, range of target, etc.

Looking for big nuggets deep is crossing over to techniques used in geophysics for locating ore bodies that are deep. Take VETEM which appears to be a standard bipolar TX design, that is claimed to be very good for targets with TCs of upwards of 1mS.

I have a prototype standard PI that is optimised for conductive objects in the 0.5 - 2mS range. No way is it in the zilch category, except for sub 10 grammers. Simulations are useful, but not necessarily an indicator of how well a practical detector works in the field.

Eric.