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Current versus Voltage


alnaimi

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Hi all,

Need ur help plzzzz :worship: :worship: , and its appreaciated ...

I have my circuit connected with LABVIEW through DAQ card , :rolleyes: in labview i just need to draw the current charastrastic and I have done the program ,,, notice that current = (VD-VDD)/R ,, I have problem it doesnot draw it ,,, I have attached the pictures of circuit and the labview program,,,,

Plzzzz need ur help ..

Thnxxxx

sorry forget the program....

this is the program

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QUOTE(alnaimi @ Feb 25 2007, 09:39 AM)

I have my circuit connected with LABVIEW through DAQ card , :rolleyes: in labview i just need to draw the current charastrastic and I have done the program ,,, notice that current = (VD-VDD)/R ,, I have problem it doesnot draw it ,,, I have attached the pictures of circuit and the labview program,,,,

I think you forgot to attach your VI.

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QUOTE(alnaimi @ Feb 25 2007, 09:39 AM)

I have my circuit connected with LABVIEW through DAQ card , :rolleyes: in labview i just need to draw the current charastrastic and I have done the program ,,, notice that current = (VD-VDD)/R ,, I have problem it doesnot draw it ,,, I have attached the pictures of circuit and the labview program,,,,

I see three things that you'll want to look at:

1. How many samples is the 'Simulate Signal' Express VI set to generate? If you're generating multiple samples, you're going to run into a problem since you're only reading one sample from your AI. You'll have no way to synchronize your data together. I'd recommend outputing a single value for Vout, then read the AI for Vin, for each iteration of your loop. This way you can synchronize your data points together.

2. Is your 'Build XY Graph' Express VI set to reset every time it's called? (I believe that's the default) I would wire a false constant to the 'Reset' terminal to ensure that it doesn't clear your graph every time.

3. Your math looks wrong in the VI. I agree that Id = (Vout - Vd) / R -- However in your VI it looks like you calculate Id = (Vd - Vout) / R

However, this would just end up inverting your results.

You look like you're on the right track -- Hope this helps.

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QUOTE(alnaimi @ Feb 25 2007, 02:55 PM)

but could u plzzzz rexplain number 1?? u mean flat sequence ??

My main concern is that you're generating x samples of a sine wave (I'm assuming x > 1). The 'Generate Signal' VI returns much more than one sample -- It's actually an array of samples -- As you'll see on the graph you have wired up to output of that VI. So, let's say you're generating a complete sine wave during each iteration. You then output that using your Analog Output. Your analog output will output the entire sine wave as it was generated. However, you then read your Analog Input at some point in time (and remember data flow -- You have no wires from your analog output to your analog input, so it's very possible that you're reading from your analog input before you output any signal!) Since you don't know what your analog output was outputing when you took your analog input sample, you really don't know what voltage (Vout) to connect that point to.

I've attached a quick VI that shows you a way to generate an entire sine wave, and then output, point by point, each value of that sine wave, while reading your Vd each time. This way, you can accurately synchronize your input and output data and create your graph.

Let me know if you're still having problems.

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QUOTE(alnaimi @ Feb 25 2007, 02:39 PM)

Hi all,

Need ur help plzzzz :worship: :worship: , and its appreaciated ...

I have my circuit connected with LABVIEW through DAQ card , :rolleyes: in labview i just need to draw the current charastrastic and I have done the program ,,, notice that current = (VD-VDD)/R ,, I have problem it doesnot draw it ,,, I have attached the pictures of circuit and the labview program,,,,

Plzzzz need ur help ..

Thnxxxx

sorry forget the program....

this is the program

Hi Noora

thanks for this site. I want to ask you did you recive data from your hardware to your program. so

I mean that did you check for that data are recieved by digital display. If your program can read data

from your measuring circuit then you may have mistake in the way of using the chart display tool.

if possible you may send to me an attachment for a picture of your program front panel and diagram

to see if you have some mistake but sorry that I use labview v.6.1 so I can not read your vi so that why I askyou to send to me a picturte. .... thanks

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QUOTE(Jeff Plotzke @ Feb 25 2007, 08:40 PM)

QUOTE(alnaimi @ Feb 28 2007, 07:08 AM)

:rolleyes:

this is THE VI , ur help is fully needed and I appreciate it 4 u all ,,, coz i am running out of time and i am new 2 labview

Alnaimi, Jeff was right.

Right click on the build-XY graph VI and configure click properties, deselect the mark:

http://forums.lavag.org/index.php?act=attach&type=post&id=5054

Ton

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QUOTE(alnaimi @ Feb 28 2007, 01:28 AM)

IT draws but not real current versus volatge ,,, any help plzzzzzzzzzz??

need it plzzz and thnx for ur time

Are you getting real values in for your current? Have you probed your analog input to verify? The graph won't show what you're expecting if you don't actually acquire that data.

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QUOTE(alnaimi @ Feb 28 2007, 08:39 AM)

u know , my curent is small coz the resistor is 47 ohm , but i have test the curent , there was ... but why not logical cuve?? do u think i need buffer??? sychronization?

You'll absolutely need synchronization between your output and your input. Otherwise, you'll have no way to accurately build your XY graph. In the VI you posted yesterday, there wasn't any synchronization -- You output 100 samples of a 10Hz sinewave and read the input each iteration. There's also no guarantee that you'll read your input after you set your output. For this reason, you need to think about these issues in this VI.

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