Recording Multiple Tasks PCI-6251

[stuee426]

I would like to display and record a frequency, analog voltage and TC temperature at the same time using a PCI 6251 and SCC-2345.  I will be measuring frequencies from 20 to 600 Hz.  I would like to record all three inputs at 10 scans per second.  I think this will need two DAQmx tasks, one for the analog voltage and TC, and another for the frequency measurement.  What is the best way to run the tasks at the same time and be able to record the data to a file at a given rate?

I am running LV 8.2.  Thanks for the help.

[Finnabon]

I found an example in Example Finder that may help you out.  The main take away from the VI is how it synchronizes the two DAQmx tasks using the Merge Error vi. 

The example is located in Example Finder >> Hardware Input and Output >> DAQmx >> Synchronization >> Multi-Function >> Multi-Function-Synch AI-Read Dig Chan.vi.

In order to write your data to file, here is an example of a good way to do that. 

http://zone.ni.com/devzone/cda/epd/p/id/5345

Allie

[stuee426]

Thanks for the feedback Allie, I am working on combining the two structures. 

 I still have a question though, how can I record data at a slower rate than I am sampling at?  To pick up a 600 Hz signal I need to sample at 3KHz to 6 KHz.  I only want to record data at a rate of 10 Hz or less to keep the file size down. 

Thanks!

Stu     

[Finnabon]

Hi Stu,

You might try decimating your data after acquisition with the Decimate VIs in LabVIEW. However, if you're sampling at such a high rate so you can accurately characterize your signal, you're going to lose that accuracy when you only record a part of that data.  To reduce file size, I would recommend using TDMS file types.  You can learn more about this here.

Allie