Null rows in output textfile

[Wilroy]

Hello LabVIEW community,

I am running LabVIEW 8.5.1 on XP. I have four analog voltage signals coming into an SCB-68 and a PCI-6259 M.

I would like to sample the four signals at 10 ksamples per sec, for a duration on the order of a couple of minutes.

I use a DAQmx read and Export_Waveforms in a while loop, as shown in the attached image (Acq.jpg).

There are blank rows distributed through out the output file, as shown in the attached image (Textfile.jpg). These blank rows

have zero values associated with them and undesirably insert zero values into the acquired signals.

It seems a null row is inserted at every iteration of the while loop. The number of null rows per occurrence and frequency of occurrence seems to depend on the sampling rate and loop execution time (experimented with Wait_until_next_ms_multiple in the loop).

I've tried to work through the Export_Waveforms vi, but am stuck in a confusion of auto-indexed loops and shift registers. Suggestions on how to remove these null values would be greatly appreciated.

Cheers,

Wilroy. 

[Karunya_R]

Hi Wilroy,

Thats excellent troubleshooting at your end. You are right about the blank lines being due to your data not coming at that point but you are still writing to the file. Have you tried to increase the sampling rate? As you increase the rate, the blank lines should be lesser frequent. 

What specific questions do you have about shift registers and auto-indexed while loops? 

Here is some help information: 

Enabling Auto Indexing for While loops