Write to measurement file timing

Question

I am trying to make a VI that allows the user to turn on and name channels through the front panel. After the user has configured the channels, they can push a button and record voltages from the enabled channels and save them using the "Write to Measurement File".vi.  I would like the user to be able to record a measurement file that is consistent in length each time they push the button...in this case, 5 seconds of data.  The current VI doesn't appear to be doing this...everytime I push the record button, the data gets recorded for 0.045 seconds.  Apparently I must be missing something as this isn't behaving how I expected it to.  See attached VI.
Attachments:
Select Channel rev 3.vi ‏244 KB

Answer 1

It waits 5 seconds then saves the last 10 samples.  Because that is the way you programmed it.  The while loop returns only the data from the last iteration.
Two ways to do what you want: 1. Read 5 seconds * 200 samples/second = 1000 samples.  No loop required.
2. Read 10 samples at a time and accumulate the data until you have 5 seconds of data.  To avoid memory reallocations the way to do this is to Initialize an array with 1000 elements outside the loop. Wire it to a shift register.  Inside the loop Read the samples and use Replace Array Subset to put the new data into the initialized array. Wire the output of the shift register to the file VI.
You generally should not put any time consuming code inside an event structure.  Read the caveats in the detailed help for the event structure.  Consider a Producer/Consumer architecture.
Lynn