LabVIEW
timer drift
We are developing a system on Labview to acquire data from several instruments by RS232 and there’s a bug we do not manage to work out. We want a 60s frequency acquisition, but each time the system logs a data string the time loop restarts with some delay, so that after the a few measurements there is a delay of a 1 second. For example :
13:43:14 108.21
13:44:15 108.22
13:45:15 108.22
13:46:15 108.22
13:47:16 108.23
13:48:16 108.23
13:49:16 108.23
13:50:16 108.23
13:51:17 108.23
Also, we would like for the system to start logging at a “round” time, for instance XX:XX:00. Is this possible ?
Below the section of the block of interest.
Thanks in advance
AVB
can you attach a real picture or (even better!) your vi?
Do you use a timed loop or just simple wait commands? "Wait for next multple" may help too...
the biggest problem is missing synchronization...
You have several parallel running measurements (no problems here). The will be executed in every iteration of the loop. But they will not stop after exactly 60s to allow file saving. That's why you get an time delay - this delay will grow with time...
One possible solution is shown in the attachment: Put the file saving in a separate loop - here no delays will occur...
It's not a perfect solution, just to show general scheme! You should also add some stop button to allow stopping your vi.
two options come to my mind:
1) round off the timestamp by using "%H:%M:00" instead of "%c" when creating the timestamp string
2) use a different wait scheme: wait until seconds=0 in the file-write loop. Use "seconds to Date/Time" the get a "date/time rec", unbundle seconds, compare...
