frequency sampling

[tajim]

Dear All!

I hope every one is doing fine!!

Well! I am a freshman of Labview and would like to have an expert view on this VI that I have made. I am trying to learn by doing!! This VI is about seeing the effects of sampling at different frequency. I have a LABVIEW 8.5 and am using a simulate signal express VI, two VIs of DAQ assistant etc. Also I am playing a bit with the number of samples and Sampling rate.

Coming to the points that I have not understood!!

1. This VI crashes and I am not able to figure out that what is the reason??

2. The time scale changes itself as I raise the number of samples even if I keep the sampling rate same.

3. Also, the peak frequency changes with the number of samples!! Why??

I hope to have your kind response!!

Thanking for your time!!

Tajim

[Morini · Accepted solution]

Hi Tajim,

Sorry about the late response. I did some modifications to your VI and it works fine.

You can begin with choosing the same Sampling Rate and Number of Samples for all three waveforms. This way everything will be sychronized to begin with.

After this you can try to change the Sampling Rate and Number of Samples for the waveforms. However you should becarefull when setting very large Number of Samples. If you have a low Sampling Rate, say 100Hz and a high Number of Samples, say 1000 samples it will take 10 sec to acquire all the samples. If the seconde DAQ assistant is running at much higher Sampling Rate at the same time you will have a DAQ buffer overflow and it might crash. Ofcourse there is ways to avoid this by implementing different structures in LV, but for this test application you should be ok if you just keep this in mind.

Thanks!

[tajim]

Dear Dennis!!

Thanks for the support!! and thank you very much for your  kind advise!!

Well! I have some more queries regarding synchronized acquisition of Force, Displacement and Temperature signals. How can I do this in time domain and as controlled by an Encoder Signal (e.g.; the acquisition of all the samples must start with the first pulse from the encoder and stop after exact multiples of the rotations (lets say 1, 2 ,3, 4 and so on) of the encoder in time domain). Could you please guide me to well explained illustrated tutorial(s)? I also want to learn what is happening in the DAQ device!! Especially with reference to the sample clock and its options such as finite sample, continues samples, on demand and hardware timed samples. 

Further, What is the efficient way of selecting a Data Acquisition System in terms of Transducer(s), Signal Conditioning, NI DAQ device, Labview and Computer hardware (RAM and CPU settings)? I am trying to educate myself using tutorials and other stuff that is provided on the web site (www.ni.com) but am not getting any where!!

I am a Mechanical Engineering and have very small knowledge of electronics and its hardware engineering. I hope you will understand my frustration as I have to learn everything from start. It would be really efficient if I could get an expert guidance on the issues that I have mentioned!!!

I hope that you could  *HELP* me!!??

tajim

[Morini]

Hi Tajim,

Depends on your system requirements(Number of channels, acquisition speed and acuracy...) we can provide you with different solutions based on different platforms. From what you wrote I think cDAQ or M-Series DAQ boards will fit your need. However if you need determinisme execution of your application you will need our RealTime platforms.

Please feel free to contact your local NI office at +45 45762600 to talk more about your application. 

You can also from Labview "Example Finder" find some example codes on DAQmx synchronization applications. Labview --> Example Finder --> Hardware Input/Output --> DAQmx --> Synchronization --> Multi Function or Device. What you need is to use the Encoder signal to trigger the Sensor Measurements.

There are some links that might help you as well:

http://zone.ni.com/devzone/cda/tut/p/id/2835

http://zone.ni.com/devzone/cda/tut/p/id/4329

Please let me know if you need more information on this application.

Thanks!

Message Edited by Morini on 04-16-2009 05:28 PM

[tajim]

Dear Dennis!!

Thank you very much for your guidance. I will definitely come back to you after I read all the information that you have provided.

Thanks again!

BR

tajim

[Rafi2003]

Hi,

I would like to experimetn, too, with this example.  When i run it on my maching I get  'sub vi is not excutable' error.  

1.  Do I need any hardware in order to run it?

2.  Can you attach this fixed vi to you mail so i can look at it?

Thanks

Rafi