strip chart keeps displaying short waveform

[Rut]

Hi,

I am trying to mornitor DAQ reading with strip chart. If the DAQ data is connected directly to a chart, then the display mode is for numbers and shows right, scrolling from left to right according to history length. But if the data is combined with time and delt T to form a waveform which is connected a chart, then the chart displays only a period of data equal to the size of sampling buffer and displays at the same location on the chart and doesn't scroll to the left. I checked the history of this latter mode, it's only 1. The former is 1024 or whatever number it's set to. Need your advice. Thanks,

Rut

[Vanessa L]

Hi Rut,

I understand that you are using a strip chart to display data you are collecting but I think I need more information about your program. Are you using a DAQ Assistant Express VI to collect the data or are you using the low level DAQ VIs? I’m also not sure what you mean by combining the data with t0 and dt to form a waveform.  Are you using the build waveform VI? The data that comes out of the low level DAQmx Read VI should be in waveform type already which is coupled with a dt and a t0. The following online knowledgebase gives some idea with the difference in chart history length if you are talking about an array of scalars or a waveform data type.

I have tried replicating your problem with both the DAQ Assistant Express VI and the example program Cont Acq&GraphVoltage-IntClk.vi (in the example finder).  When plotting just the regular waveform data type in both cases, the data moves from right to left and the length of the graph shown corresponds to the chart history length that was set.  If you could post the code that you are dealing with, it might make it easier to understand and reproduce on our end.  Thanks!

[Rut]

Hi Vanessa,

I am using a 3rd party DAQ that uses its own driver. I am clear now what the problem is: I didn't read the circular data buffer correctly. The DAQ updates only a portion of the buffer, but I plotted the whole buffer each time. So it looked wierd. Also there was some timestamp problem caused by the incorrect reading, which could be solved by initializing the timestamp only once in the beginning.

Thank you for your kind reply and I will keep you posted if new issues come up.

Rut