I was doing order analysis on some motor run-up run-down data ( from 200 ~ 5000 rpm). It was noticed that when dealing with run-down data (defined as starting rpm 4900, ending rpm 200), the calculation stops at around 2000 rpm. The help file said that the rpm channel has to be equally spaced, but I tried multiple things, including generate a straight line rpm channel but still had no luck. If I reduce the window size (say, from 4096 to 2048), the ending rpm will go down some, but still not to the specified end value.
I finally inverted the rpm and signal channel (made the “run up”) then did the same analysis (starting at 200, ending at 4900) and it worked.
Why?