random delay in reading triggered AI

[rvleadmal]

Hi,
I am using DAQmx for a digitally triggered analog aquisition (n channels, n samples).For repeated aquisition the program works correctly if the interval between triggers is small(like around a second). However if you leave about 4-6 second gap between triggers there is about 200ms delay before it starts aquiring. I.e.the graph shows that the aquisition started from t = 200ms instead of from t = 0. (This does not happen all the time but happens with resonable frequency.

i am attaching the VIs I've made. The main VI is called skeletonv2.0. (The other 2 are sub VIs used in the main VI)

NI Software : LabVIEW version 7.0
NI Hardware : Multifunction DAQ device PCI-6023E
Driver Version : 7.0.0f0
OS : W
indows 2000

[rgharrison]

Hi,

I've taken a look at your code and I ran it on my machine to see if it would demonstrate the delay but I didn't see it happen. I tried retriggering it quickly and then more slowly (>5s) and it still seemed to give me proper data. What I suspect is that you have residual data from the previous acquisition still in the buffer. It could also be that although you have a separate group of data on each trigger, the program is considering it as a continuous operation so the next group of data is added to the previous group.

It is unlikely to be a hardware issue. It has more to do with how the data is interpreted by LabVIEW and the charts in LabVIEW. How much data are you reading on each successive trigger? Maybe you can adjust the chart history leng
th by right-clicking on the chart. Another consideration is the speed of your computer; How fast is your processor and what amount of memory do you have? This might help determine the timing discrepancy in the chart.

One suggestion is to clear your chart history before you display the next trigger's worth of data. You can create a property node of the chart (right-click >> Create >> Property Node) and select the property to clear the history of the chart right before you display new data. I have a feeling that this will do the trick. Anyway, hope that helps. Have a good day.

Ron