Essentially most field sales people are chosen from within, usually the applications engineering department . I was in the premier applications engineering group, and had been in the position for about 8 months, with a total of 1.5 yrs in the department before I interviewed for the position. These positions can sometimes be posted online, but usually external candidates are only hired in niche and undesirable locations or if there is no interest internally. To get a field sales position, know a wide variety of NI's products and understand why someone might use a digitizer vs. a general DAQ board, vs. a DMM. Know controls concepts such as HIL, closed-loop control, have some "elevator pitches" prepared, such as "What is teststand?" or what differentiates measurement studio to labwindows/cvi etc.