Implement Metal detector circuitry in LabVIEW

[DPARK]

04 and 05

[johnsold]

AWG 30 wire is rated for about 140 mA in coil or transformer applications according to a handbook I have.  So 0.5 A pulses seem rather large unless the duty cycle is very low.

Counter Output is the output from a counter circuit or device and typically varies dynamically as the counter counts.  Electrically the output driver may be very similar to a "Digital Output."  The Digital Output is driven statically from a boolean signal (or a numerical value representing a group of booleans simultaneously).

Lynn

[johnsold]

While I was creating my reply above you were posting some scope images.

1. How are you getting 50-60 V signals from your 12 V battery?  Does the scope think you are using a 10X probe when you are connected directly?

2. The 03.jpg shows a substantial amount of ringing at about 5 times the frequency of the excitation.  Try putting some resistance in parallel with the receiver coil, perhaps 1000 or 10000 ohms.  See if that damps the oscillation more quickly.  Then perhaps you can see some effect of metal.

Lynn

[DPARK]

Thank you so much... That was 10x... 😞 I am sorry.

Okay, here is the new data (with a 1k resistor parallel to the receiver coil):

I can get a chance in the received signal if i move metal about the coil, but between the coil and the metal can't be more than 5 millimeter... 😞 Not very efficient...

Please see the new values at the pics:

Simon

[johnsold]

OK.  Now you have a system which actually has all the necessary parts and it just barely works.  Before your system did not work.  With a working system you can begin to optimize.

Try different orientations of the coils and the metal target.  Try different duty cycles. Try different values of the resistor parallel to the receiver coil.  Make measurements.  Keep records. Analyze the results and use the analysis to predict what other changes to try.

Lynn

[DPARK]

Jap, you're right! Thank you so much. 

But what I also need and even can do at the moment is to create the software. I think I have to do FFT now to get the amplitude etc. Is there anything else I need?

I absolutly want to get it into LabVIEW for my project. Thats my goal and then you're release from that! 🙂 🙂

Thank you. I tried to sent you a 20mb video that you can see exactely what happens in case there is metal... It's to big for attaching...

Simon

[DPARK]

It's again me....

I am not really pleased about the response of the coil. I don't get really a signal. Just in case that the metal is between the crossing area of the coil. So it's not really the

effect of determine metal (and not an air cora coil), that's more like a transformator (with a metal core)... How could his happen?! I even don't know what signal I get from the RX coil...:(

Maybe you also have an advice for that...

Simon

[Henrik_Volkers]

I put your schematic into LTspice, with a pulse length of 1ms you get around 500mA , if you put the damping resistor in series with the diode the rise time of your pulse is not affected. However for 500mA don't make it greater than 30 Ohms, otherwise your Voltage at the drain of your FET get to close to the U_DSmax according to the spec of the FET.

And you should add the 100nF and the 100µF (or 2 -3 47µF) not very critical, to lower the internal resistance of your battery 😉

OK your real voltages will look different 🙂 since all the parasitic are not included ...

Now you have pulses. With 12V and 20Ohm coil resistance you can't get more than 500mA and longer pulses than  1ms don't give you more current.

Without iron/metal place your coils to minimize readings. Try a 1k, 10k or 100k  to 'shortcut' the reading coil, your scope has a higher sensitivity that your DAQ ... 2mV??   so use it.

I'm still curious about the not working shielding......

V(n002) is U_DS (measured between coil and FET to GND)

[Henrik_Volkers]

Maybe it's a good idea to move the coils away from your batt,scop,pc, powerline cords ..... 1m can help a lot 😉 how long is your cable?

[DPARK]

You're so awesome!!!! Thank you!

Hey, before I wanna try your new circuitry I'll get 5V to the digital output. As I mentioned, I currently use the "DAQ assistant" with the "counter output" because the 

created puls signal seems to be okay. But I only have a 2.5V voltage on the DAQ board output. How could this happen? I absolutely want 5V to trigger the MOSFET.

Can you tell me how I can get 5V to the ouput? I already read that this must me possible the the DAQ as a maximum digital output voltage of 5V...?!?!

To the shielding: I have to insulate the both shielding wires in the most sensitive crossing area of the coils. And... I should use always the same ground... Actually, I connected

3 different GND's for my circuitry. Maybe that's why it didn't work. 

Please let me know about the DO voltage of 5V, otherwise I only got a 6V voltage due to the battery... and not 12V....

Thank you so much!

Simon