Breakthrough!!!!! Full discrimination with PI

[Aziz]

Hi porkluvr,

I know I will probably be embarrassed by the obvious simplicity of your answer, but I can't stand it any more.


Tinkerer, WHAT IS "TEM"?

Have a look into this poster:
http://www.zonge.com/PDF_Papers/TEMposterAs.pdf

Well, we call it TEM transmitter, because it is a tuned electromagnetic transmitter. There is obviously confusion with transient electromagnetic. But the output of the transmitter is also a transient electromagnetic pulse. This transmitter allows very high current pulses with less power consumption due it's high power efficiency. It is the most efficient TEM transmitter which is possible.

PS: Sorry Tinkerer, but I could not resist to answer his question.

Aziz

[Aziz]

Hi Tinkerer,

thanks for your efforts.

A more interesting spot would be just right after the maximum flyback voltage. Even the coil current I gets zero at this maximum flyback voltage, this has no relevance. It is the coil current change (dI/dt), which matters. Right at this point (I=0), it achieves it's maximum dI/dt even.

So the sampling window must be later than the maximum flyback voltage. Targets would be haven charged longer either.

Aziz

[Tinkerer]

Hi porkluvr,



Have a look into this poster:
http://www.zonge.com/PDF_Papers/TEMposterAs.pdf

Well, we call it TEM transmitter, because it is a tuned electromagnetic transmitter. There is obviously confusion with transient electromagnetic. But the output of the transmitter is also a transient electromagnetic pulse. This transmitter allows very high current pulses with less power consumption due it's high power efficiency. It is the most efficient TEM transmitter which is possible.

PS: Sorry Tinkerer, but I could not resist to answer his question.

Aziz

Thanks Aziz, saved me some work.

From many posts across the forum, I can see that many people would appreciate an explanation of frequency domain and time domain and how these domains apply to the PULSE INDUCTION METAL DETECTORS.

I will start a new thread for this subject. However, I am not good at explaining things, so I really depend on people like you, Aziz, to make the subject understandable.

Tinkerer

[Tinkerer]

Hi Tinkerer,

thanks for your efforts.

A more interesting spot would be just right after the maximum flyback voltage. Even the coil current I gets zero at this maximum flyback voltage, this has no relevance. It is the coil current change (dI/dt), which matters. Right at this point (I=0), it achieves it's maximum dI/dt even.

So the sampling window must be later than the maximum flyback voltage. Targets would be haven charged longer either.

Aziz

Thanks for the feedback.

I agree with you that other sample spots may give different results. This is why the first series of tests will use 5 different samples during the TEM pulse, as mentioned in my post above.
Eventually, every part of the cycle will have to be sampled to look for the information that it might offer.
The different frequency response appears at different times along the cycle timeline. By different frequency response I mean the different TC's of different targets appear at different spots in time along the whole TX - RX cycle.
I am anxiously waiting for Moodz FPGA to do the more intricate sampling. For the time being I am just trying to show the potential, enough to entice others to experiment with this exciting TEM method.
Thanks again Aziz for having explained and analyzed the TEM METHOD for all of us.

Tinkerer

[Aziz]

Hi Tinkerer,

..
However, the thin steel gives a positive response when presented flat to the coil. Therefore, the discrimination at this spot in time is not perfect.
..

this is exactly, what I have observed too. It's when the eddy current response (resistive response) dominates over the reactive response.

Nevertheless, we need to sample over many time windows to get all informations about the target.

Aziz

[porkluvr]

I will start a new thread for this subject.

Tinkerer

No. Don't. Stop.

Don't go overboard. A quick explanation of an alternate usage of the acronym TEM was good.

[Tinkerer]

Here are the test results for the sample taken at the time, 4 to 9uS after switching off.
Annexed is the picture showing the TEM pulse and the sample pulse.

The TEM pulse is really the Flyback that has charged the TEM capacitor. So the flat part at the left of the picture is the end of the TX charge, the coil charge current has reached it's maximum. At switch off, the Flyback is absorbed by the TEM capacitor.

I have added some more targets to the test.

The results:

12mm diameter steel ball ........................ not detected
13mm diameter lead ball ......................... 1mV positive
Crown cork flat ..................................... 4mV positive
Crown cork vertical ................................ 2mV negative
21mm diameter round PCB ....................... 1mV positive
21mm diameter copper coin ..................... 3mV positive
1 Gram gold bar .................................... only just positive

As we can see, a sample taken at this spot in time does not show much target response.

Observing the signal shape on scope screen I can see that the responses could be improved by taking shorter samples.

Tinkerer

[moodz]

Thanks for the feedback.

I agree with you that other sample spots may give different results. This is why the first series of tests will use 5 different samples during the TEM pulse, as mentioned in my post above.
Eventually, every part of the cycle will have to be sampled to look for the information that it might offer.
The different frequency response appears at different times along the cycle timeline. By different frequency response I mean the different TC's of different targets appear at different spots in time along the whole TX - RX cycle.
I am anxiously waiting for Moodz FPGA to do the more intricate sampling. For the time being I am just trying to show the potential, enough to entice others to experiment with this exciting TEM method.
Thanks again Aziz for having explained and analyzed the TEM METHOD for all of us.

Tinkerer

I am working on it ... coding coding coding ....slaving over a hot computer ....

[Tinkerer]

Here comes the next sample down the timeline.
Sample 9 to 14uS
The target response is quite a bit different from the sample before.

The results:

12mm diameter steel ball ........................ 1mV negative
13mm diameter lead ball ......................... 3mV positive
Crown cork flat ..................................... 5mV positive
Crown cork vertical ................................ 12mV negative
21mm diameter round PCB ....................... 2mV positive
21mm diameter copper coin ..................... 8mV positive
1 Gram gold bar .................................... 2mV positive

This sample does not give much new information, but I include it so an not to leave any gap in the sampling sequence.

Tinkerer

[Tinkerer]

Today we look at a SWEET SPOT on the TEM TX PULSE timeline.

Sample 17 to 22uS

The results are different from the other spots. Specially the difficult target, the crown cork shows good discrimination or differentiation.

Here it does give a 0 positive response, only a strong negative response.


12mm diameter steel ball ........................ 4mV negative
13mm diameter lead ball ......................... 3mV positive
Crown cork flat ..................................... 0V
Crown cork vertical ................................ 22mV negative
21mm diameter round PCB ....................... 2mV positive
21mm diameter copper coin ..................... 11mV positive
1 Gram gold bar .................................... 2mV positive

When we look at the changes in response between the different sample spots, we see that some type of targets show little difference in the response along the timeline.

Other targets show much more difference. This is an indicator that different factors have a different influence on the target and that, if we know how to interpret these differences, we can read information about the target.

Full discrimination is all about information about the target.

Tinkerer