SFT systems have two independent onboard systems operating in concert with each other. Transmission Error (TE) measurement and Torsional Acceleration (TA) analysis. The concept of transmission error (TE) measurement is to capture, with rotary encoders, the rotational geometrical deviations between two gears relative to an ideal rotation. The torsional acceleration (TA) measures the change in rotational speed over time (dynamics), often used to analyze gear meshing impacts and their noise behavior. TE represents the cause (real geometrical deviations), while TA shows the effect of such a TE at higher speeds and loads.

This TE technique is better suited to measure and detect lower-order errors such as: single-flank total composite action, single-flank tooth-tooth action, single-flank runout, single-flank circularity, and single-flank concentricity. TA is to use a method of rotational synchronous time signals, with data collected from torsional accelerometers, to focus on NVH-related issues in the measured component. These errors can be time domain-based errors like nicks or gear modulation due to runout and circularity, and they can be order domain-based errors like gear mesh energies, side bands, and ghost orders. These order domain errors can occur on a sub-micron level.