How do I associate timing with multiple AI loops that is independan​t of loop execution speed

Question

I am using Labview 7.1 and I am performing AI of
voltage on different channels of the same multifunction DAQ.  I am
using while loops to aquire the data.  I am writing the data to
spreadsheet file with an associated time as a 2D array.  Currently I am
using the 'elapsed time' interactive subVI to get the time in seconds
(attempting to use the 'Get Date/Time in seconds' and converting it to
DBL results in time values that do not change. My thoughts are that
maybe the number of seconds is too large to display single second
precision with a DBL floating point number). When I run AI on two
multiple loops they execute at different rates and thus the time values
from "elapsed time" are accumulated at different rates. I have tried
using timed loops to control timing, but if one loop executes at a rate
slower than the timing of the loop the 'elapsed time' still accumulates
at different rates.  I need to be able to associate both analog inputs
to the same time
value in the spreadsheet value and I would like to find a way to
associate a time with each data point that is independant of loop
execution speed (although I would still like to control execution speed
of the loops. I am pretty new to Labview and programming in general,
any help would be greatly appreciated.

Answer 1

If you want to read more than one AI at the same time, you should use a trigger.  You would need to set up the AI Trigger to an external source.  Then you would have to use a function generator or digital out to create a clock.  The clock would be wired to the AI external trigger.  When the clock goes high (or low depending on configuration), both AIs would read.  That is the method I use when needing to sync multiple AI inputs.
- tbob
Inventor of the WORM Global