Implement Metal detector circuitry in LabVIEW

[DPARK]

Hey Lynn,

basically, I achieve a very slow voltage from the receiver coil due to the inductance of the coil. This signal depends very strong of the coil position und therefore I balanced the coils for a minimal received voltage.

The expected signal depends of course very strong to the kind of metal. But it shouldn't be task to distinguish between them. So, If I see a vary in amplitude, I know there is metal. This should be all. Additional, it would be great to add a filter to reduce noises. 

My proplem is, I don't know how to get the amplitude from the "whole" signal und how to control a LED in case there is metal.

Basically, I heard a lot of "amplitude modulation" but isn't that just used if I also want to discriminate metals?

I hope you can help me with the components. I' ve never learned LabVIEW but I wanna try it.

Please see the attached document to see my point of view.

Thank you so much!

[johnsold]

OK.

1. What is amplitude?  For a sinusoidal signal the formula is v(t) = A*sin(w*t).  A is the peak value of the signal v(t).

2. What is variation in amplitude? A change in A over time.  If you collect enough data to contain several complete cycles (and the noise is small), then the A for that data set is approximately the maximum value of any of the data points.  If the A' for a subsequent data set is different from A, then you have a variation in amplitude.

3. Use a shift register to pass the value of A from one iteration of the loop to the next.  Compare current value to previous value and decide whether metal has been detected.  You may want to keep several previous values of A, depending on how vast the metal or coil moves.

4. Do you have some kind of fixed impedance between the generator (AO) and the coil so you can see the change?

To learn LV start with the online tutorials.

Lynn

[DPARK]

Hmm.. okay... I understand you until the time depending of the Amplitude.

Why should I keep an eye on the current levels? I don't really understand your instruction.

What komponents are used for that in LV?

At the moment I get a very low voltage signal at a high frequency...

[johnsold]

The output of the analog output device acts like a constant voltage source.  No matter how the impedance of the coil changes (within the limits of the AO device), the voltage remains the same.  To measure the effect of bringing metal near the coil (which changes its impedance), you can put a resistor in series with the coil.  The voltage drop across the resistor will change with the coil impedance giving you a measurable signal.  This is part of the external circuitry, not part of LV.

Lynn

[DPARK]

Ahggg... I thought I can create a sinusoidal oscillation with the device... Okay, but why should I use a resistor and not a capacitor? Shouldn't I achieve a oscillating signal with a LC-resonat circuitry?

I know what impedance is but do I have to calculate it for my case? I am not sure...

Thanks so much for your help.... I really appreciate it.

[DPARK]

Please see also the attached picture to understand the assembling.

I hope I mentioned that I have a Transmitter coil (Tx) and a Receiver coil (Rx). So the "produced" voltage is due to INDUCTANCE between the coils. 

Thank you!

[johnsold]

You can create a sinusoidal signal with LV.  It will probably not be an oscillator in the usual sense.

Rather than trying to guess what you know and do not know frmm your comments and your VI, please tell us about your background.  What do you know about electrical circuits, especially AC circuits with inductance?  What do you know about measuring changes in inductance?  Please post an image (.png preferred, NOT bitmap) of the diagram of your coil and the connections to the DAQ device(s). What kind of DAQ devices do you have?  What other electrical measuring devices do you have available?

Lynn

[DPARK]

That's what I tried with my VI. Therefore I used "Simulate Signal" and connected it with the device "NI USB -6212" analog output.

Alright, I am a student in mechanical engineering and now I am working for a research projekt. I chose a "electrical" project to get more experiance in this field. But I only have basic knowlege and I calculated a few resont circuitries during one semester. So I only understand basic's of that. 

My problem is I have to finish this project soon, so I can't learn all the things in two weeks. I try my best but this isn't a project to learn LabView etc... 

That's to the background...

So I basically know how to deal with AC circuits because I already calculated impedance etc... I know that are komplex calculations. 

A attached a picture. You can see all devices I can use. I also worked with a signal generator device, but I don't have it now...

It must be possible to create a oscillating signal, transmit it to the analog decive output and to the transmitter coil. Due to inductance of the two coils I get a changed oscillating signal from the receiver coil. If I move metal about the two coils, I can already determine a change in the amplitude of the received signal. Can I not use this change of the received signal for my VI? ... 

Thank you

[F._Schubert]

I've been busy with my work, so sorry about coming back late on your problems.

You won't be able to get this osscilating because your feedback will be to slow (unless you compile it on an FPGA). For this you would need to use an analog amplifier.

As you mentioned you have little time left, I try to give you a push in getting at least something done in this project. To make it a bit easier on the software side, you should try to get your sine generator back. It is possible to do it with the DAQ as well, but having a sync of analog output and measurement requires some low level DAQmx functions and can't be done with the DAQmx assistant.

What I basically suggest you to do is a frequency sweep. If you already can control the sine generator with LabVIEW, you can automate it, otherwise just make a user interface to type in the frequency. For each frequency, you recorde amplitude and phase. Step up the frequency on a logarithmic scale.

At the end, plot Amplitude vs. Frequency and Phase vs. Frequency. You should see the resonance peak in the amplitude.

Now do the same with some metal in the detector and have the same measurement.

Felix

[DPARK]

Okay... Thank you!

The problem now is:

I definitely can't use the signal generator the next 2 weeks... But.... I also have a amplifier in the lab. (see picture)

I tried to work with that but I didn't really find there are changes... I just get a "short" signal... 

That means now, I have to create the signals with the board. I really need your help. This is beyond my knowledge

in this short time... I am sorry. I try to keep as much as possible in mind...

Thank you Felix!