Signal analysis VLF-Detektor

[Qiaozhi]

Thx, that's even more accurate. I built up housings for three different coils. So I'll try the coplanar (concentric), and DD in three different sizes with varying frequency.
My problem is, how can i assume the capacity and at least the inductance? Isn't 5.433mH is much? I thought about 350uH...

Thank's for your help! I really apprechiate it

350uH is more appropriate to a PI detector. The TGSL, as an example, uses 6mH for the TX coil and 6.5mH for the RX.

[SIMONN]

350uH is more appropriate to a PI detector. The TGSL, as an example, uses 6mH for the TX coil and 6.5mH for the RX.

Oh okay... And what about the capacity? Do you calculate the value with the "Medhurst"-formulary?

[Qiaozhi]

Oh okay... And what about the capacity? Do you calculate the value with the "Medhurst"-formulary?

[SIMONN]

Ye, that's obviously... But I just have have the frequency and wanna try to get the inductance. But you assumed the capacity of 47[nF]. How could you assume this self-cpapcity of the coil? There are many different formulary for approximation...
And also the resistance of a 30 AWG wire is about 20 [Ohm]...

[SIMONN]

Qiaozhi,

I got a lot of information about the TGSL detector in the board and now Igot a second fundamental question to you:

Actually, is it possible to determine and discriminate metals just with the coils? That means I don't use the detector...
A signal generator creates a signal to the Tx-Coil and I meassure the receiving signal with a oscilloscope. I also wanna use the received data in LabVIEW with a "synchronous demodulator" in order to discriminate through a case-study.
But is that a working alternative to the whole detector (PBC, etc etc) ???

Please give me a request what you think about it...

Thanks!

[Qiaozhi]

Ye, that's obviously... But I just have have the frequency and wanna try to get the inductance. But you assumed the capacity of 47[nF]. How could you assume this self-cpapcity of the coil? There are many different formulary for approximation...
And also the resistance of a 30 AWG wire is about 20 [Ohm]...

47nF is not the self-capacitance of the coil. This is the capacitor you need to put in parallel with the coil to form a tuned circuit.

Qiaozhi,

I got a lot of information about the TGSL detector in the board and now Igot a second fundamental question to you:

Actually, is it possible to determine and discriminate metals just with the coils? That means I don't use the detector...
A signal generator creates a signal to the Tx-Coil and I meassure the receiving signal with a oscilloscope. I also wanna use the received data in LabVIEW with a "synchronous demodulator" in order to discriminate through a case-study.
But is that a working alternative to the whole detector (PBC, etc etc) ???

Please give me a request what you think about it...

Thanks!

If LabVIEW can simulate the circuitry of the detector, then yes. You need a pre-amp to amplify the signal from the RX coil, followed by the synchronous demodulators and also the filter stages, etc. Have a look at the TGSL information for more details ->
http://www.geotech1.com/forums/showthread.php?t=15710

[SIMONN]

Thank you so much!
So, I totally underestimated this kind of project... Actually I thought I can use the received signal from Rx-coil to get the whole information from the amplitude and the phase lag...

So, I'am not sure if it is possible to "create" the detector cirtuitry with LabVIEW, but otherwise I'll have a problem with my project.

I'll read through your attached doc and come back with many questions. Thanks so much for your help!

SIMONN

[SIMONN]

So, I read through the document...

But what's basic set-up now? If I also build the PCB and at least the whole circuitry of the detector, why do I need the pre-amp and the synchronous demodulator etc? I can discriminate between metals if I build up the whole detector?

I saw "flow digramms" like this set-up: (attached picture)

[SIMONN]

Or at least one basic question:

How much hardware do I need? According to the picture above I don't need the whole detector. If I can create the blocks like filter etc in LabVIEW. I can do that, but not design the electric circiutry...

Just for your information:

I compared the received signal from the Rx-Coil with the original signal from the signal generator. If I move metal about the coils, I can determine a tiny vary in the amplitude. Can I really not use THIS RECEIVED SIGNAL from the Rx-coil? I am sad and sorry to "spam" you with questions. But I definitely need help for this student project... A "one-man" project

[kt315]

Can I really not use THIS RECEIVED SIGNAL from the Rx-coil?

yes, certainly. you can not. if you will take PI mono coil you do not feel to need using THIS RECEIVED SIGNAL from the RX coil. then ... you would need to re-go on the another class of detectors.

[SIMONN]

Can I really not use THIS RECEIVED SIGNAL from the Rx-coil?

yes, certainly. you can not. if you will take PI mono coil you do not feel to need using THIS RECEIVED SIGNAL from the RX coil. then ... you would need to re-go on the another class of detectors.

... and don't have the possibilitiy to determine between metals.

Or is it possible to discriminate with the PI detector? I don't think so...

Thank's so much for your help. I only can see one option for me: Build up the TGSL (VLF) detector completely and discuss the data in LabVIEW. But it doesn't really make sense for me to do that with LabVIEW, because once I make the "whole detector" it can discriminate between metals and so I don't really need it digital.

But that's the basic condition of my project...

[SIMONN]

Hello together,

I am back with more results for my project. But I need your help again wit hthe signal analysis. That's my point of view:

1. I create a digital puls signal trought a "data aquistision! (DAQ) board and drive the gate of a MOSFET with that.

2. Because I need more current to drive the coils, I used my MOSFET as a switch with an external 12V (1.3Ah) battery.
(see the link:
http://static.electro-tech-online.co...itch-n-fet.png
load = transmitter coil, micro = DAQ board)

3. please see the attached picture to see my received signal from the receiver coil. I don't know, but I can't really determine metal.

I only get a chance in the (blue) receiver signal, if I put the metal in the crossing area of the DD-coil. (It's the same effect like a metal core coil. But I can't determine metal if the metal is not in this zone.

Do you have an idea how this could happen? I don't know what's wrong...

Thank you all!

Simon

[SIMONN]

and there the effect in case I get a change in the received signal.

Please give me a respone to my signals.
Thank you

[Qiaozhi]

Simonn - please keep your posted images to 800x600, not 4800x3600 (or whatever it was exactly).

I have modified your last 2 posts to correct the problem. As you can see they are still very readable at this resolution.

Some questions:
Where are you sampling the received signal?
Or were you expecting to see a change visually on the scope?
Are you using a damping resistor?

[SIMONN]

Simonn - please keep your posted images to 800x600, not 4800x3600 (or whatever it was exactly).

I have modified your last 2 posts to correct the problem. As you can see they are still very readable at this resolution.

Some questions:
Where are you sampling the received signal?
Or were you expecting to see a change visually on the scope?
Are you using a damping resistor?

Oh... That's great. Thank you Qiaozhi.

Actually, the received signal is parallel connected to a 1k resistor.So, that's the parallel signal from the resistor and the coil?!
And yes, I expected to see a chance in the amplitude?!?! But there is nothing as long as the metal is not in the "crossing section" of the coils...

Oh, before I forget: The shielding of the coils. I put both shielding wires together (as you can see on the picture) but if I connect the shield
with any GND, the signal is clear away....