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If a gear tooth is damaged, the assumption is that, when engaged, it produces a waveform that is distinctive from the average. However, the transmission’s vibrations spec-trum is complicated by the many simultaneously meshing gears, and often these details are obscured, even after time-synchronous averaging. As was shown in the previous sec-tions, special processing tools are needed to isolate the dy-namics in order to be able to apply condition indicators to the individual components.
Typically, measurements are taken and the condition in-dicators are applied to the TSA signal. As mentioned pre-viously, this technique has been ineffective for planetary transmission prompting the need to use vibration separa-tion. In implementing vibration separation, a higher level of discipline is required in order to maintain proper index-ing of the transmission’s system with measurements. Some special precautions include maintaining gear stage orienta-tion during overhaul, a method to identify the correct spline to use when swapping different sun teeth, and the use of a planetary reset pulse that ensured that measurements begin when the transmission is in the pre-determined orientation. Because of these extra efforts to implement vibration sep-aration, an alternative method to transmission diagnostics was made possible. One that exploits the geometric syn-chronization between the sensors and planetary geometry that allows simple TSA data to be revisited.

The technique relates subsets of the TSA signal to the individual sun teeth in mesh. Figure 23 shows an enlarged view of the sun gear region for the OH-58C con.guration. At any given time, the sun gear is in mesh with four plan-ets. Due to the non-sequential nature of the OH-58C, the engaged planets are in different meshing positions along each tooth making it dif.cult to determine which teeth are ”most in mesh.” To eliminate ambiguity, the lines of centers between the sun and planets are used as references. The centers of each planet are tracked during meshing and then mapped to a region on the sun tooth. The sun gear angles in mesh at any given time gives the center of each individual mesh bin whose width is one sun gear’s pitch. A group of simultaneously meshing mesh bins is called a mesh group.
　
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