Hi ku2,
So what exactly do you mean by functioning incorrectly? The nature of the incorrect behavior will help determine where the issue is. Note that the speed of your while loop is highly limited by your use of Express VIs which can take a fair amount of time to execute.
So, low RPM acquistion now works correctly, but you cannot increase your sample rate past 10 Hz? Let us know what incorrect behavior means in this case and hopefully we can figure something out.
Cheers,
Andy C.
Applications Engineering
National Instruments