Monitoring oscilloscope with labview 7.1

[gigi85]

thank you 🙂

I re.ask my new problem again 🙂

Is it possible obtain what kind of waveform i'm seeing on the scope?

 i'd like that labview tell me if what i see is sin, square, etc waveform 

is present a specific driver for this or i have to do it by myself?

if i have to do by myself in which way can i treat overshoots?

[Aojha]

If you have only two types of input like sin and square then you can take FFT ( if it gets single frequency its Sin else Square). If you haveother types of inputs also like exponential and ramp then this method would not work.

Probably you can design your own rules with the help of Waveform monitoring VI's under Waveform pallete

[gigi85]

i have square and sawtooth waveform

[Aojha]

If Square and Sawtooth have aprrox. same frequency then slope of square will be order of magnitude higher than slope of sawtooth. You can use transition measurement VI to get the slope. But if frequency is also varying then this method will not work.

[gigi85]

i have to check if a signal is only square or sawtooth...i could have a range obout their real value.

so that i made a vi to detect if my waveform is a square (i check if rise time and fall time are less of a certain value and i check that all my values of my waveform are in a certain range...in this way it works... 

but i have a problem with a sawtooth...i could make the same thing, checking only max and min value, fall time and rise time...but in this way i can see only if it's a sort of a sawtooth...maybe it's only similar, slow in a phase and fast in the opposite one.

but i want underline that as input i can have all sort of waveform, also a random signal

[Aojha]

Let's remove random signal from disscussion.

1- Do FFT=> Signle Frequency=>Sinusoidal

Multiple frequency

1- Check slope and frequency=> calculate slope/frequency=> No. greter than a certain value Square

 No. less than that value could be Sawtooth or random (most probably Sawtooth).

These can be performed for basic testing.

To check for rest you will have to do more tests and update yourself when new input comes.

But if amplitude and frequency of input can be calculated then FFT of individual input will be distinct.

[gigi85]

could you explain me better what i have to do? in theory and in labview...

thanks

[Aojha]

The time domain and frequency domain properties of a signal are related through their fourier transform.

Fourier transform is unique for any type of signal (Be it sin, square, ramp or any other).

I don't know if LabView has some inbuilt function to detect incoming waveform, but you can use FFT (Fast Fourier Transform, frequency spectrum) ssignature to distinguish between Wavforms.

For example pure sine will have only single frequency. If you see the spectrum of Square and Sawtooth you will find the difference in their spectrum.

You may also search for fourier transform of different waveforms and use as your check to detect input signal.