Hi bsteinma,
By default, the waveform graph will just
graph the set of samples that is given to it, which will be changing
for each iteration as you read new samples, and it formats the time
axis to correspond to the dt value of the waveform. You can actually
change this to display the absolute time by right-clicking on the graph
and selecting Properties. In the properties window, select the Display Format tab and make sure the x-axis is selected (please see attached screenshot "graph_properties.png" ). You can then select absolute time,
and you will see the axis change to correspond to the actual time of
your measurement (based on the t0 and dt values of the waveform).
However, even with this method, you will still only be graphing the
last set of data you read. If you want to see the data accumulate with
time, you will need to use a shift register and keep building an array
with data (not ideal for long period of time as the array gets large
and needs to be graphed each time), or use a waveform chart instead.
Regarding
your initial question about writing the time values, I would suggest
using the Export Waveforms to Spreadsheet File VI, which can be found
in your functions palette under Programming » Waveform » Waveform File I/O.
You can just wire your waveforms to this VI and specify to append the
data to the file (please see attached screenshot "wfm_sprdsheet.png" ). I also prefer to
turn off writing the header, otherwise a header will be inserted into
the file for each loop iteration and it is not as clean. Also note that
you will have to change the formatting of the cells in Excel to display
the time properly (I had to create a custom format of the form h:mm:ss.000 AM/PM
to view the time with the proper millisecond resolution). Please let me
know if this answers your question, or at least provides a good
starting point.
Regards,
Daniel S.
National Instruments
