Measuring PHASE SHIFT IN PI

[simonbaker]

Gday Simon, yes like i mentioned in the other thread we need a test standard so we can all test the same things & confirm results.

Why don't we just start off with a circuit--say Gary's _Chemelec PI circuit or something, everybody can assemble it cheaply & were under way?

It is all very confusing when we all have different & varying circuits to test with.

Many heads are better than one, especially mine.

Sounds good if there is agreement - can you post a link to the essential info for Gary's _Chemelec PI circuit ?

-SB

[Qiaozhi]

Tinkerer, is there another file format you can attach your findings with, can't open the files?
I couldn't open the last PDF for some reason either?
Thanks

The most likely reason you cannot open the spreadsheet is because Tinkerer has saved it as .xlsx, which is the new format for Microsoft Excel files. The same applies to Word documents as well. They are now saved as .docx by default.

Fortunately the world of open source software comes to the rescue. Just download OpenOffice from www.openoffice.org and (despite what Microsoft tells you) you can open these files without any problem. You can even save them in the more familiar .xls format. See attached file.

[Qiaozhi]

I had a very tiring work day today, so I have to leave some questions unanswered.
It would be nice if somebody could coordinate and organize all the information that comes together here.
Here is a test sheet of some time ago.

Tinkerer

To make this information more effective we would need measurements taken at various distances from the coil. The current spreadsheet only shows the results when the targets are 1.25" away.

[Tinkerer]

Ok - but this thread is derived from some other thread, so good to repeat the essential information, like what is basic circuit for tests, test points, idea we're discussing, what coils (single, double, balanced, etc). Just hard to follow otherwise.

Regards,

-SB

Simonbaker,

We will move fastest ahead, if we divide the work load between us.
If you write a resume of our present position, I could correct errors and we would have a unified information sheet.

Tinkerer

[Tinkerer]

Gday Simon, yes like i mentioned in the other thread we need a test standard so we can all test the same things & confirm results.

Why don't we just start off with a circuit--say Gary's _Chemelec PI circuit or something, everybody can assemble it cheaply & were under way?

It is all very confusing when we all have different & varying circuits to test with.

Many heads are better than one, especially mine.

Hi B^C,

I suggest we use my own. The others will not fit.
I have posted the power supply circuit some time ago. Since then I have made some changes, I will update the schematic and post again. We start with that.
Have you sorted out the problem with opening the files?
Do you have any suggestions what format I should use so that the files can be opened by everybody?

All the best

Tinkerer

[Tinkerer]

Hello Tinker, SB and BC,

Great thread. As mentioned by robbi_h in the other thread resistive ground minerals on IB or normal PI are a problem. You may want to make up a jug of salt water for testing. This can be made by pouring a whole can of salt into about 2 liters of water. This will simulate a weak resistive ground mineral, you will have to deal with it the field or beach. It will show a signal between 1 - 5uS. after a voltage transition. Unfortunately its in your zone of interest 2.5uS. Keep it going.

Regards Mark

Hi Mark,

thanks for the input. I know the resistive ground problem, having used metal detectors on the bottom of the oceans for many years.
I would be interested in suggestions of how to simulate this effect in the lab.
I am curious also about the phase shift it will produce on my experiment.

Tinkerer

[Tinkerer]

To make this information more effective we would need measurements taken at various distances from the coil. The current spreadsheet only shows the results when the targets are 1.25" away.

I fully agree with you. The 1.25" distance is not a good one anyway, but, since I am still experimenting with the coils also, I assemble the coil arrangement only with one plastic screw in the center, no epoxy, so I can easily dismantle and rebuild different size coils.
So this plastic screw nut prevents me to locate a target closer than 1.25" to the coil. It is only a problem with very low gain and very small targets.
I am going to make a draft test schedule and post it. Then we can all agree on the parameters and can repeat the tests to compare results.

In the meantime, would you be so kind to write the "Hymn book" for us?

All the best

Tinkerer

[simonbaker]

Simonbaker,

We will move fastest ahead, if we divide the work load between us.
If you write a resume of our present position, I could correct errors and we would have a unified information sheet.

Tinkerer

I would like to do that but I am so new to PI circuits that I will be too slow and probably misinterpret.

Off the top of my head, I'm aware of a number of different PI design topics:

1. Differential vs. grounded PI coil designs.
2. One vs. two coil designs.
3. "Balanced" RX coil design (I guess nulled like with VLF detectors).
4. Center-tapped coil vs. no center tap.
5. Distributed capacitors (in coil) vs single capacitor.
6. Sampling during TX on pulse vs. sampling after TX pulse turn-off.
7. Target modeling; slow vs. fast targets.
8. Importance of "flyback voltage" magnitude and duration.
9. Techniques for adding discrimination to PI detectors.
10. Possible misconceptions, myths involving "charging" the target, etc.
10. Others...?

I think the main point of this thread and Tinkerer's recent thinking is related to subject (6) and (10), how to add discrimination to a PI detectors.

I think Tinkerer started looking at the TX on pulse sampling as a possible way to gather more information that could lead to discrimination techniques.

Along the way, he observed what he believed was a stronger target response to the on-pulse than the off-pulse.

This lead to wondering whether the target "Tau" (time constant) caused a stronger response to "slow" pulses than fast pulses; was there some truth to "charging" the target; were eddy currents during TX pulse on-time helpful or harmful to overall detection, did they enhance or suppress the target response during the turn-off pulse.

Aziz did some Spice simulations with different targets and TX pulses, but I'm not sure what the conclusions were.

Tinkerer has been testing target responses and gathering some data on different targets using a test setup that I think is a TX coil with targets placed very near (or in) it. I'm not sure whether there is a separate RX coil or if it is "nulled" (balanced) to the TX coil. Qiaozhi wants to see how the data changes if the targets are at varying distances.

I know I missed out many important topics.

For me to understand better I'd like to know exactly what the experimental setup is (circuit, target, etc.) that we are talking about, and a clear statement of the question or theory. Photos, circuit diagrams, graphs, etc. would help greatly making it clear and easy to remember.

Regards,

-SB

[simonbaker]

Hi B^C,

I suggest we use my own. The others will not fit.
I have posted the power supply circuit some time ago. Since then I have made some changes, I will update the schematic and post again. We start with that.
Have you sorted out the problem with opening the files?
Do you have any suggestions what format I should use so that the files can be opened by everybody?

All the best

Tinkerer

Hi Tinkerer -

I recommend you save the files to ".csv" format; most spreadsheet software can read that in easily, and in a pinch it can be read in any text editor.

Regards,

-SB