how do i acquire the generated signal?

[pomplamoose]

ladies and gentlemen, i'm a bit of a novice in LabVIEW although i practice solving more or less difficult problems, i got NI cDAQ-9178, have connected input with output channels and after making a working scheme on acquisition the signal and on generating separately, i decided i could successfully combine the two schemes and obtain the generating-acquiring system. hell i didn't know it wouldn't work. there is probably a lot of things im doing wrong in this case, so any andvice or help directly with the .vi i've attached to the message would be soo appreciated. thank you.

[KateB]

1. Which module you use for AI and AO? Don't tell me it's 9178, since that's chassis model.

2. What is an error message shown?

[pomplamoose]

Hello, KateB,

im using module NI9269 as AO and NI9205 for AI, sorry, i thought the info on the model of chassis model was neccessary 🙂
the problem is there is no error messages, it just does not for the reason unknown to me acquire the generated waveform, check the vi attached, 

Thank you 😉

[KateB]

Check already and found nothing wrong. Further check...

1. When you said you make it work separately, how do you actually do it?

2. This may sound a bit annoying, but I need to know how do you connect the signal between modules?

3. What does it show on frontpanel when you run a VI?

4. Can you add error cluster boolean to loop condition in below loop as upper loop? The problem may come from below loop, but never pop up, since you don't do any error handling in below loop.

[pomplamoose]

1. When you said you make it work separately, how do you actually do it?
i could see the waveform which was generated by the AO channel by just connecting a signal generation to a DAQ assistant VI for generation, then i placed the acquiring DAQ assistant and connected the output to the waveform chart - seems legit. now im trying to make it with those blocks as in .vi ive attached, so that it wouldn't show me a buffer overflow error, as it for some reason does. i was given an advice that if the same scheme was made with those blocks, there could be a separate buffer block where i could establish the buffer size. so i started working following the same logic: not connecting the generating and acquiring parts of the scheme together as i thought they were already connected to each other with real wires. but it doesnt work. 😞

2. This may sound a bit annoying, but I need to know how do you connect the signal between modules?

the output channel(in my case ao0) is wired to the input channed ai0.  i have wires of two colors - red and white, so the the red wire from the ao0 on 9269 goes to the ai0 on 9205, the white wire goes from ao0 to COM thing on 9205. im might be giving some irrelevant info - just trying to be as specific as possible.

3. What does it show on frontpanel when you run a VI?

i have two charts to control the similarity of the signals. for instance when i did the same with DAQ assistant blocks i generated a square wave with freq=1 to be able to say if its true for a real time change of the signal every second. then i moved to making a scheme with those blocks and now i see clearly a good generated square wave and i see that nothing is being recieved - its just drawing a line, like the voltage does not change.
4. it does not work either, i took the lower loop from the labview examples, and tried numerous changes such as placing a lower loop in the while structure of the upper loop, removing elements, swapping them, all the things a novice could think of 🙂 including removing the clear task block along with the error message block - no errors, and nothing works. btw it didnt show any error with the error block, so i thought the problem is that the AI somehow doesnt see the AO could it be it?

forget about annoying me, feel free to ask any neccessary questions, im realy curios about all this data acquisition thing and i'd really love to improve my skills 🙂 thanks you, again and again 

[KateB · Accepted solution]

One thing I suspect is that your generated frequency is not suitable with #S and Fs you configured. You may try #S=10k and Fs=100k.

[pomplamoose]

did i get you right? #s stands for number of samples per channel and Fs is sampling frequency?

and one more question: after determining the appropriate number of samples and sampling frequency, how do i determine the buffer size correctly corresponding to the characteristics above? thank you

[pomplamoose]

yeah it really worked, but now i face another problem: the generated signal starts at 0 and runs with specified amplitude and frequency, but the acquired signal starts at 10.7. so i went down to NI MAX and checked the settings of the input channel and saw the following: the voltage range is -10...10 V but with differential terminal configuration voltage is somehow still 10.7, then i switch it to RSE and it goes down until it reaches 1 V as i configured, so i thought, maybe i should switch terminal config to RSE in my labview scheme, i double-clicked on AI channel and AO channel, switched both to RSE, but when i run it, it switches back to default automatically, and the voltage is again above maximum - 10.7V. 😞

[pomplamoose]

problem solved although i still have to make sure i understand what is the difference between differential, rse and nrse config 🙂 thanks, KateB, kudos! 

[KateB]

Sorry for late reply. Stuck in BKK rain. BTW, glad to hear that the problem is solved. Cheers!!!