Why is measuring a frequency so slow?

Question

If I don't measure a the two frequency's I can get the program to write data about 7 times a second, but with the frequnceys it is only 1 or 2 times. Take a look at the program to check this out. Also on the graph there seems to be a buffer over run, data is written the the wrong side of the graph first.
Attachments:
twin_turbo_wo_water_to_air_data_output.vi ‏192 KB
create_data_string_II.vit ‏24 KB
Measure_freq_--_Sub.vi ‏46 KB

Answer 1

There is still a VI missing from your list so I could not run your code. In the future consider saving your top level VI with "save with options">> development distribution. This creates a library of all the VIs.
You are using write characters to file.vi. This VI opens a reference to a file, writes the data, then closes the file. This makes the VI very slow. Consider opening the file outside of the loop, writing to the file inside of the loop and closing when your are done. Open up the write character to file to get an idea of the VIs you will need.
This kind of operation is usually best done using parallel loops--one loop for acquisiton and one for data storage. The tricky part is that you will need to use queues to transfer the data between the l
oops. There are several excelent LabVIEW shipping examples of how to use queues. Open LabVIEW >> help >> examples >> optimizing applications >> sync. tasks.
The queues will speed your code and reduce the buffer overflows because your data will be pushed into the queue as it is aqcuired and can be written to file in larger pieces speeding the write process.
Jeremy