Problems making an curve tracer with the add-on Digilent VI

[Whens_Wens_Day]

Hello to all,

I know this is quite a begginer or maybe an obvious question but i really need help with someone pointing it out.

Recently im trying to make an expansion for the Analog Discovery 2 to make it able to caracterice an transistor with a Vce more than 5 V, up to 36V and a base current instead of simply a Vb, for my final year project.

How to caracterize the transistor

I managed to made a prototype of the hardware and Im trying to control it with Labview, the setup is like the image.

This setup should be correct as i tried it in Waveforms from Digilent

But when I did the Labview block diagrams, it does not give me the curve as i expected. I think the problem is in how I plotted the results, which made a lot of trouble.

The main loop prepares to read the channels 1 and 2 as well generating the functions W1,W2, but Im not quite sure what i did with the results are correct, as well for the plotting, as I see it only always overwrite the plot.

Plot from Labview

Any suggestions please?

[GerdW]

Hi Day,

---

@Whens_Wens_Day wrote:

But when I did the Labview block diagrams, it does not give me the curve as i expected. I think the problem is in how I plotted the results, which made a lot of trouble.

The main loop prepares to read the channels 1 and 2 as well generating the functions W1,W2, but Im not quite sure what i did with the results are correct, as well for the plotting, as I see it only always overwrite the plot.

Any suggestions please?

---

Right now you show the lastest curve data in your XY graph. Nothing less, and nothing more…

What's the point in collecting your measurement data in growing 2D arrays when you plot just the data of the current iteration?

(Maybe you should append new data to a 1D array instead of building 2D arrays?)

[Whens_Wens_Day]

Hello there,

I spent some time debugging the program and managed to make some progress. First, I discovered that I had missed a wire. Second, I noticed that the functions responsible for sampling from the analog channels—channel 1 and channel 2—were acquiring both signals and indexing them into the same waveform data. I was able to separate each channel and obtained the following results:

This makes sense because those are the waves I generated.

Now, I see that the issue lies in how I plot the samples. Since I’m overwriting the XY plot each time, I’m only displaying the last group of data. For example, I can see this:

For the first loops

Some loops later

Finally

So that means the way i store data and plot them is the problem, now how should be the flow to save data and then plot them all together?

For now Im doing this:

But its not right, so how should be a classic loop and plot diagram look like? It doesn't mather if i plot the data in the current iteration or outside it.

Wen

[Whens_Wens_Day]

Hi all,

I finally got it:

But there i still have some trouble when changing with the plotting, if i change the plot type lining the points into a curve:

So now Im trying to acces the array data that makes this plot, is there a way to acces it?

Wen

[GerdW · Accepted solution]

Hi Wens,

---

@Whens_Wens_Day wrote:

But there i still have some trouble when changing with the plotting, if i change the plot type lining the points into a curve:

---

Two options to avoid those interpolation liines between the curves:

• create separate plots for each curve
• separate the data of each curve with a NaN point, when you put them all into one plot. NaN samples will not be plotted in the graph…

[Whens_Wens_Day]

Hi GerdW,

Thank you for your help, now it works as I want.

Sincerely,

Wen