The IME is a very suitable device for gearbox monitoring. Ideally an IME is fitted to both the input shaft and the output shaft.
The IMEs monitor the condition of the bearings on the shafts they are attached to. Precision angular measurements on both shafts measure the total wear on the drive train through the gearbox. Torsional vibration information derived from the angular measurements will give an indication of problems in the gear train.
Contaminant particles in the lubricant passing through the bearings, and between the gear teeth may be detected, signs of potential bearing faliure.
In the case of systems where the output shaft is both driven from the gearbox, and drives the gearbox (under running and over running) as in helicopter main rotors, the total drive slack in the train may be measured each time the drive load changes.