The 10Hz Bearing That Broke Everything
You inherit a vibration monitoring script written in 2015. It uses raw FFT, hardcoded 2048-point windows, and zero overlap. You think "I'll just swap in scipy.signal.welch() — it's the modern way, right?" Then you push to production and the false alarm rate triples.
This happened on a pump monitoring system running 24/7 on an edge device. The old FFT code was brittle and ugly, but it worked. The Welch replacement looked cleaner, followed best practices, and completely missed a bearing fault that the legacy FFT had caught for three years straight.
Here's what I learned migrating five different legacy vibration analysis scripts to modern scipy APIs. Some of it wasn't in the documentation.
What the Legacy Code Actually Did
Most industrial FFT code from 2010-2016 looks like this:
python
import numpy as np
# Legacy vibration FFT (circa 2015)
def analyze_vibration_old(signal, fs=10000):
"""Original FFT-based analysis — do not modify (in production since 2017)"""
---
*Continue reading the full article on [TildAlice](https://tildalice.io/fft-welch-legacy-vibration-migration-pitfalls/)*
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