Yes we use a accelerometer and it integrates to velocity.
coming to planets,in first stage we have three planets and in second stage we have four planets.This gearbox is a movable gearbox where some pressure is applied for grinding(Normally runs between 10 to 15 mm/sec vibration).
You may want to request the anticipated frequencies from the manufacturer Eichoff.
Based on earlier information, the 2nd stage has ring = 74 teeth, planet = 27 teeth and the sun = 18. If your tooth counts are correct, that may mean you have a non-factorizing gearset in the 2nd stage.
In a non--factorizing planetary gear train the the number of teeth on either the sun gear or ring gear is not evenly divisible by the number of planets. In your case both the sun (18T) and ring (74T) are not divisible by 4. A non--factorizing system is theoretically smoother and quieter than one that factorizes for torsional
vibrations, but will cause increased lateral vibration. In a factorizing arrangement, the tooth actions of the various planets are synchronized, tending to produce a cyclic beat. Having said that ANSI/AGMA states "The benefit from hunting and non--factorizing is theoretical, without experimental verification."