Digital counter data is not written into a file

Question

Hello
I'm a beginner with labview and I'm trying to make a measurement program for my setup (sensor data -> file). I have the USB-6008 and I'm trying to save data from  a digital counter and 3 analog ports. The counter is for RPM and the number of revolutions. Analog is used for force, potential voltage and temperature. Currently data from the analog ports is written to a file normally but all the data from the digital side is lost. So in the measurement text file columns for the digital data are empty.
The DAQ assist for the counter is set "on demand" but the analog DAQ assist has a sampling rate of 1k (continous). My problem propably comes from the different sampling rates. I could set analog sampling to "on demand" but I need the 1k rate for the measurements. Also making two different measurements files works but it's very inconvinient.
Am I right about the sampling rate and how would I fix this?
Attachments:
measurements.vi ‏144 KB

Answer 1

Think Data Flow.  For a Loop to "loop", everything inside the loop must execute.  Furthermore, since your loop starts with "Acquire one sample" and ends with "write one sample", the time for the loop to execute will be the sum of the times to sample (1 msec) + write (??).
Take advantage of the fact that LabVIEW in inherently parallel.  Instead of taking one sample/loop, take (say) 1000, but do not write them in the same loop.  Instead, "export" them to a parallel loop (via a Queue) so that when the 1000 samples arrive, they are written all at once.  While it is true that to acquire 1000 samples at 1KHz will take 1 second, most of that time will be spent "waiting" for the next sample to be taken (it takes almost no time to put a point on a Queue).  Similarly, if I have a whole second to write 1000 points to a file, that's more than enough time.
Separating "serial" tasks into parallel streams is a common LabVIEW Design Pattern called the Producer/Consumer pattern.  There are numerous examples of this pattern, including a template that will write the basics of the code for you (open the File menu, choose "New...", From Template, Frameworks, Design Patterns, Producer/Consumer Design Pattern (Data)).  A slightly more sophisticated example can be found by starting LabVIEW, New Project, Continuous Measurement and Logging. 
Bob Schor