Generating a non-periodic analog signal from a file while keeping track of sample number sent

[giogonza]

Hi every one. I'm really new in Labview and maybe my question is trivial for some users but I'm still having a hard time trying to figuring out how to get this done in Labview.

This is my situation:

I got a huge text file with 650000 samples that belong to a non-periodic signal. We need to read from this file and generate an analog output by reading its values (file is a cvs format) and then recreate the signal by doing periodic D/A conversions (this is not an issue). This analog signal is going to serve as signal generator for the analysis of one of our medical devices (signal is an ECG record).  At the same time, we are going to read from the serial port of our PC to get the responses of the UUT to the stimulus.

Since the timing between the samples has to be deterministic (timing is critical for our application) I plan to use hardware-timed generations by using the onboard clock of my DAQ device to synchronize the D/A generation. The issue is that we need to keep track of the sample number that is being sent to the UUT at any particular moment because we plan to compare our signal values with the responses obtained from our UUT so in that way we can analyze if its behavior is erroneous or correct. How can I achieve this? Once I send a block of samples to the FIFO buffer of my DAQ card for the generation I lost control over the sample number that is being sent.  The reason why I need to have control over this is because some of the samples are annotated and they serve as reference for the analysis of the UUT

Any ideas on how to accomplish this?

These are my settings: Labview 8.2 professional, Windows XP, and a PCI MIO16E card. Sample fs is variable 128sps<fs<1kps. FIFO size 512 samples.

[Nathan_R]

Hi giogonza,

            Assuming you are using the NI-DAQmx drivers there is a DAQmx write property that returns the total number of samples generated since the start of the task. This will let you keep track of how many samples have actually been generated. To access this property use a DAQmx Write Property Node. The property you want is Status»Total Samples Per Channel Generated. I believe this will do what you need. Let me know if you need any more help.

Thanks,

Nathan

[giogonza]

Hi Nathan, Thanks for your reply.

I tested the option you gave me and it works fine but just for the first cycle of my waveform generation.  The problem I'm facing right now is that the file with the data values has to be read in a cyclical way. So once my DA is done with the first 650000 samples the program has to point to the first sample again and some how I need to reset the "counter of the total of samples per channel generated" to keep track of the second round of values . My program keeps incrementing the value of the "counter of the total of samples per channel generated" for the second, third, and n cycle of my generation. Is there any way to reset this value? or any sugestion on how to acomplish this?

Thanks your your help!

[Nathan_R]

Hi giogonza,

The only way I know to reset the “total number of sample generated” is to start and stop the task. I’m assuming you do not want to do this because you don’t want to interrupt your output. Another option would be to divide the total samples by your file size using the Quotient & Remainder block. This will let you keep track of the number of samples output this cycle of the file as well as the total number of cycles outputted. The screen shot below shows an example of this. Let me know if you need any more help and have a great weekend.

Thanks,

Nathan

Message Edited by Nathan_R on 02-15-2008 12:41 PM