The easiest way to do this is if you have a function that relates voltage to pound force. You can enter this directly into your task configuration and get pound force from your DAQmx Read rather than voltage. If you cannot come up with a function, then a simple table lookup is an alternative. You can do this in your LabVIEW code by using the Interpolate 1D VI (Mathematics -> Interpolation & Extrapolation).
Note about your code: When your data acquisition starts you have no way of stopping it. The inner loop as a True wired to the conditional terminal, which means it's an infinite loop and the code will not respond to you pressing the Stop button on the front panel. Instead of placing the buttons inside a cluster leave them free so you can read the Stop button inside the inner loop.
