field test unit no 001 "model T"

[Aziz]

BTW,

the integrator in the front-end is also limitting the detectable frequency response. Most aren't even well designed to get the high frequency components. I dare to say, that most PI detectors can't detect bandwidth of greater than 100 kHz.
*LOL*
Aziz

[Aziz]

as if you have any idea
Why does every troll have to pose as a stuffy professor, or as a nagging woman :duh:

This guy/girl is looking for the "Made in Germany" WBGB technology.
*LOL*

PS: Due to bad behaviour of patent trolls, the technology isn't published to date.
If I would do this, someone would steal and patent it with no shame.

[Aziz]

I'll have to disagree with this. On most PI detectors the "detection bandwidth" through the sampling integrator(s) is only 100Hz or so. The same can easily be true of direct sampling with an ADC. That is, if you synchronous sample a single point 10us after the flyback then the required ADC BW is very low. So do you still need more than 100Hz BW on the transmit?

No, I meant the bandwidth before the synchronous demodulation occurs.
Does it make sense to transmit at frequencies, you can't detect at all?
Clearly not. Just save the TX power energy or use it additionally in the frequency range, you can detect.

Aziz

[Carl-NC]

Bandwidth limitting makes sense.

Consider, you have a TX transmitting a wide band pulse, let's say 10 Mhz bandwidth (ultra fast coil).
And you can detect only a bandwidth let's say 1 Mhz bandwidth.
Does it makes sense to transmit the other 9 Mhz bandwidth too?

No, not at all. You could move the "wasted" transmitted energy into the frequency region you take the measurements. And you have more bang to the targets.

Fortunately, the coil with it's parasitic capacitances and damping resistor forms a low-pass filter, which is limitting the reasonable frequency response into the 500kHz to approx. 1 MHz region. If you are not using (sampling) this frequency region, you are just wasting TX energy.

I'll have to disagree with this. On most PI detectors the "detection bandwidth" through the sampling integrator(s) is only 100Hz or so. The same can easily be true of direct sampling with an ADC. That is, if you synchronous sample a single point 10us after the flyback then the required ADC BW is very low. So do you still need more than 100Hz BW on the transmit?

[Davor]

Don't talk about GB with me then, Aziz. Talk to the members of this forum and explain where, with a PI, the X component is coming from for Ground Balance.

as if you have any idea
Why does every troll have to pose as a stuffy professor, or as a nagging woman :duh:

[Davor]

We have a damping period of 6µs - 10 µs until we can get some samples.

You can observe this as a successive process. Let me get there... There is a pulse, a dead period, and a sample. For every subsequent sample you can also observe it as a very same process: pulse, somewhat longer period, sample. For each such sample you have successively lower high frequency content information.
Now, considering first sample as a combination of sample time (~1us) + waiting time, and frequency content as ~1/T, there is a significantly lower frequency content in each of such samples than the sample time (~1us) may suggest.
It also appears that fourier may not be the best transform for such samples.

[chudster]

Back again.

... Where is the significant upper frequency limit?

Consider the following practical example:
We have a damping period of 6µs - 10 µs until we can get some samples. While looking at the coil current slope (dI(t)/dt), we can expect of having not much significant high frequency components after the flyback period. The later sampling times eating a lot of high frequency response and we effectively end up of having maybe a bandwidth of 200-400 kHz.

So 1 Mega samples/s is just an overkill and should be enough for experiments.

Aziz

I think Carl explained it well in his post. It depends on the approach you take and also whether you integrate or demod the signal in some way and then sample that.

A low sample rate with a few samples at strategic times is possible and approximates sample and hold techniques of some analog circuits. Another way is to ask what is the target signal, determine the highest freq components in that signal (including "features"), sample it to the digital domain and with an accurate representation of the signal "oscilloscope style" it can be processed as wanted digitally. This seems to be the approach Moodz is taking and is the approach I would have expected for the UMD (that's the Ultimate Metal Detector). A direct sampling approach seems to indicate 1MSPS to 2MSPS.

Chudster

[UrbanFox]

Why should I talk about GB with you? You won't get my WBGB.... but the Chinese.... or the QED2 dev team...
MUHAHAHAHAHAHAHA

Don't talk about GB with me then, Aziz. Talk to the members of this forum and explain where, with a PI, the X component is coming from for Ground Balance.

[Aziz]

OK Aziz, a legitimate question which I am sure forum members would be interested in hearing an answer to.

If we are talking PI, where does the X component come from for Ground Balance???

Why should I talk about GB with you? You won't get my WBGB.... but the Chinese.... or the QED2 dev team...
MUHAHAHAHAHAHAHA

[Aziz]

Hey, using the semi analog-digital demodulator/modulator concept, we can modulate four samples into a stereo input channel of the sound card. That should be enough.. It will even work with two samples only (high frequency/low frequency components).

One of the highlights of the Tablet PC processing is, that you can make everything in the software!!!
Cheers,
Aziz

[UrbanFox]

Back again.

While I ignore Ufox (he can't even write my name)
Aziz

OK Aziz, a legitimate question which I am sure forum members would be interested in hearing an answer to.

If we are talking PI, where does the X component come from for Ground Balance???

[Aziz]

Back again.

While I ignore Ufox (he can't even write my name), we have to talk about the TX frequency response further. Where is the significant upper frequency limit?

Consider the following practical example:
We have a damping period of 6µs - 10 µs until we can get some samples. While looking at the coil current slope (dI(t)/dt), we can expect of having not much significant high frequency components after the flyback period. The later sampling times eating a lot of high frequency response and we effectively end up of having maybe a bandwidth of 200-400 kHz.

So 1 Mega samples/s is just an overkill and should be enough for experiments.

Aziz

[UrbanFox]

The truth is: reliable discrimination can't be implemented.

But the ground balance can be implemented (by separating X and R) and the relation of X/R (or vice versa) gives a good indication to discriminate iron/non-iron targets. It might work for most conditions. But can fool you too.

Aziz
PS: We have a very nice weather here. I'm heading for a walk.... Cheers.

We are discussing PI aren't we??? Where does the X come from for Ground Balance???

[Aziz]

Thanks. Do you suppose that time position and time duration of signals contain useful information for target identification or this is something too variable to rely on this for target identification?

The truth is: reliable discrimination can't be implemented.

But the ground balance can be implemented (by separating X and R) and the relation of X/R (or vice versa) gives a good indication to discriminate iron/non-iron targets. It might work for most conditions. But can fool you too.

Aziz
PS: We have a very nice weather here. I'm heading for a walk.... Cheers.

[WM6]

The other concept is using an integrator, which is integrating a "spectral response" depending on the time position and time duration and the frequency response of the integrator

Thanks. Do you suppose that time position and time duration of signals contain useful information for target identification or this is something too variable to rely on this for target identification?