When testing bearings I have noticed that if I press down with some extra pressure - I get a change in dB reading as opossed to letting the weight of the probe "rest" on the bearing housing.

Has anyone else experienced changed readings with additional pressure?

Terry O

Terry,

Yes, this can be a common problem to achieve repeatible measurements. I believe there can be two effects present:
1) If high vibrations (g's acceleration) are present, then the probe tip can bounce off the surface and give false reading.
2) Hand conduction/damping and deformation of the probe/sensor can change its response.

Mounting/holding an ultrasound sensor should be done with the same care that one uses to hold a vibration sensor or to ensure that an accelerometer on a magnet base is firm and not rocking.

Walt

As Walt points out a magnet would be a preferred method. However, most are not using magnets, I often tell my students when possible use a motor such as grinding motor. You know those "dual" wheel grinding motors most shops use to sharpen or buff a piece of metal, etc... Or, you may find a good bearing and using a enough pressure to hold the point of the ultrasound sensor to the bearing surface acquire a decibel number. Now, have the rest of the technicians find that same decibel number or reading, once they have found that same decibel reading remind them to take "note" of how much pressure they used. Practice this a few times and everyone should be on the same page.