Your VI diagram is password protected, thus rather useless. Can you elaborate what you get when "it does not work" (e.g. wrong result, no result, error message, etc.).
I've never had a problem with the plain vanilla "threshold array" included with LabVIEW. Of course it only finds the first zero crossing that goes from negative to positive so you need some extra coding to make it find all the others, e.g. in a loop increment the start index to the rounded up fractional index output to find the next zero with positive slope. Repeat until the end of the input array is reached. etc. Then repeat with the array multiplied by (-1) to get all the zeroes with negative original slope.
