DAQmx Timing of Counter and Analog Readings

[Maverickous]

Hey all,

I am starting a new post about a topic I have been getting help with. Attached it my latest VI. Its pretty close to what I need it to go.

The TDMS file attached had a "Write Time" of 2 seconds, and an "Idle Time" of 5 seconds. I forget what I had the clock rate at, I don't think it was 5000, as it shows now in the VI, but it could have been.

Anyways, as you can see I don't have an equivalent amount of data in my five columns. I realize that only the Analog DAQmx task has a specific timing attached to it, but I was under the impression that one timing source dictated the loop time. This is clearly not the case. In theory, I would like to have multiple points of data per cycle, not ~30 cycle jumps in time and cycle count and a mass of data that I no longer have anything to plog against.

What am I missing? I have a physical function generator that the CI is reading, should that be the timed input and use that frequency as a trigger for the Analog stuff? It seems like that wouldn't be enough data.

I am so close to having this VI doing what I need it to do, just need a little help getting this bit sorted out. Thanks.

Previous foum thread: http://forums.ni.com/t5/LabVIEW/Clock-Rates-and-Periodic-Data-Logging/td-p/1829789

-Lyric

[Maverickous]

Hey all,

[Maverickous]

I am starting a new post about a topic I have been getting help with. Attached it my latest VI. Its pretty close to what I need it to go.

The TDMS file attached had a "Write Time" of 2 seconds, and an "Idle Time" of 5 seconds. I forget what I had the clock rate at, I don't think it was 5000, as it shows now in the VI, but it could have been.

Anyways, as you can see I don't have an equivalent amount of data in my five columns. I realize that only the Analog DAQmx task has a specific timing attached to it, but I was under the impression that one timing source dictated the loop time. This is clearly not the case. In theory, I would like to have multiple points of data per cycle, not ~30 cycle jumps in time and cycle count and a mass of data that I no longer have anything to plog against.

What am I missing? I have a physical function generator that the CI is reading, should that be the timed input and use that frequency as a trigger for the Analog stuff? It seems like that wouldn't be enough data.

I am so close to having this VI doing what I need it to do, just need a little help getting this bit sorted out. Thanks.

Previous foum thread: http://forums.ni.com/t5/LabVIEW/Clock-Rates-and-Periodic-Data-Logging/td-p/1829789

-Lyric

[Maverickous · Accepted solution]

Hey all,

Quick update. I hooked up a second function generator to a PFI port on my DAQ and made a sample clock for each channel type (AI and CI), then pointed both clocks at the same port. Bingo, I have the same number of samples in each column, and the data looks correct.

So lesson learned: you can use the same external clock, but not the same internal clock for different channel types. Neat trick.

--Lyric