ORDER TRACK ANALYSIS - rmpordermap

Hello everybody,

I am working on a real-time acquisition system (National instrument having 4 input analog channels) which aims at performing some vibrational analyses in real time. The data are acquired at 51200Hz and I am acquiring the accelerometer output and the primary speed. However, I do not have a tacho signal and therefore I am using the analog primary speed to perform the analysis.

More specifically, I am using rpmordermap by giving as inputs the accelerometer signal, the primary speed (analog signal) collected every second.

My problem is related to the fact that the main amplitude response do not correspond to a theoretical order (i.e. I exepect to have a high order amplitude at 15th order, but this shows at 14.96).

Does anybody know to what this might be related?

Thank you all for any answer