can anyone tell me why i am not getting signals in seprate graphs

[malik123]

hi

i am stuck with one basic problem, actually i am using NI USB 6212 DAQ with my labview8.6, what i am doing is of getting two different analog signals on ai0 and ai1 simultaniously and showing them on two seperate waveform graphs, i use this split signal and array index both to solve the problem but it is still showing me only one signal on both graphs instead of showing me two different signals on either graphs. can any body tell me what i gonna do now, is there any problem with my DAQ device i just brought it few days back, or should i have to include any thing in software,?the test vi is attached.

waiting for good response

[dousley]

Hi Malik.

I took a look at your code. I think it will work. In fact, it does work with the hardware I used at my desk. That leads me to wonder if there are any surprises to the wiring you have going to your module.

As a cross check, I would suggest that you bring your whole acquisition into one graph and see if your two inputs look different there. If they don't, maybe the signal you're giving to your first channel is the same as the signal you're giving to the second channel. Perhaps they are shorted together somehow. That would be my first guess.

I hope that's helpful.

Daniel O

Conditioned Measurements

[malik123]

hi dousley

thanks for the reply

thats why i am surprise too, why it is not working, let me explain it to u a bit. i have two function generators that r connected with the pin Ai0 and Ai1 respectively, i have tryed both signals seperatly than it is Ok, but when i want use both channels then it makes problem,

now come to the hardware side may be that has some thing to do,

the senario is that i connected my first function generator Positive (+) to Ai0(+) and the function generators negative is connect with Pin (AI GND) same with the other function generator i put the positive to Ai1(+) and ground the other pin to (AI GND),

so this is the whole hardware picture, now can u have some idea if i am doing some thing wrong with this settings?

looking forward

Regards

[dousley]

So when you only connect the Function Generator #1, then you get the correct waveform on Graph #1? And when you only connect Function Generator #2, you get the correct waveform on Graph #2?

When you connect both function generators, does the signal look like Function Generator #1 or Function Generator #2? Or does it not look like either one?

[malik123]

both waveform graph#1 and graph#2 shows the same out put of Function Generator#1 even though both are connected on there respective inputs, and  if i change the frequency of the Function generator#2 it only distort the signal on graph 2  instead of appearing, but  if i disconnect function generator#2 during running state it again shows the out put of FUnction generator#1 on both graphs.

[dousley]

A few more questions that might help:

1) What is the configuration for your input channels? Which channels? Single ended? Differential? What input range? What frequency?

2) What is the configuration of your sources? What output impedance for each one? Floating outputs? Single ended or differential?

3) What happens if you disconnect Function Generator #1 and just connect Function Generator #2? Does it's waveform appear on either graph?

[malik123]

answer1: i have tryed with both single ended and Differential? right now i am using differential because there is no such effect, input range in 10 to -10 volts

answer2: Function generator #1 has 10 Hz frequency output differential, output impedence 50ohm amplitude 8Volts

           and Function generator #2 has 100 Hz frequency output differential, output impedence 50ohm amplitude 5Volts

answer3; when i did that as u mentioned it shows me the output of Function Generator#2 on both graphs,

[dousley]

Thank you Malik. That is some good information. It's especially interesting to note that either function generator seems to be driving the other input. It sounds like there is an unintended electrical connection. Like the channels are shorted together, or something kind of like that. You had FGEN#1(+) going to AI0 and FGEN#1(-) to AI GND, and FGEN#2(+) going to AI1 and FGEN#2(-) going to AI GND,... correct?

When you switched to using a differential input (so FGEN#1 goes to AI0 and AI8, FGEN#2 goes to  AI1 and AI9) the channels became separated like you had originally planned? 

Well, if you don't mind, I do have another question just out of curiosity. If you have the board running an acquisition in your original setup, disconnect the function generators. What resistance do you measure between AI0 and AI1 (or whatever your input channels were)?

Daniel

[Jeff at home]

Malik--

I just took a look at your example code.  The problem is in the index array function.  You've left both indicies at default so you are returning (from top to bottom) Waveform(0) and Waveform(-1).

You want to return Waveform(0) and Waveform(1).

Good luck! 

[Dennis_Knutson]

Jeff,

You might want to review your LabVIEW basics. When you leave the inputs unwired, the first output returns element 0, the second output returns element 1 (not -1), a third output would  return element 2, etc. There is nothing at all wrong with the index array function as it is being used.