Do ION7550 and ION7650 meters use cosine (cos) or sine (sin) based Fast Fourier Transform (FFT)?

Issue

What do ION7550 and ION7650 meters use for Fast Fourier Transform (FFT).

Product Line

ION7550/ION7650

Environment

Configuration

Cause

The user want to know how the meter uses FFT

Resolution

The FFT decomposition in the ION7550 and ION7650 meters use a cosine based function. The latest firmware for the 7550/7650 (v350 and above) also notes in its code comments that sine inputs are rotated 90 degrees to compensate for the cosine based FFT function. In other words, they are translated into cosine functions to keep unity.