We are about to start monitoring a machine with big journal bearings (~ 2 foot dia journals, 0.018 inch diam clearance), but are limited to mounting accelerometers on the bearing housings.
The frame is QUITE substantial. I'm expecting if we had prox probes measuring the journals they'd report 0.002 inch or less orbit. I expect the 1X casing vibration will be a lot less. Wild guess maybe 10-to-1

What are some relative measurements others have experienced?

Thanks,

Dan T

Dan, you don't give a speed but with two foot journals and a reasonable sliding velocity in the bearings your speeds are probably 1000 RPM or less.

Proximity probes are highly recommended in this instance. If you anticipate 2 mils shaft relative and a 10:1 ratio to the case then you will get the equivalent of 0.03 g on the casing (assuming 1000 RPM). Tough to measure!

As an aside, you probably aren't far off on the 10:1 although needless to say on this forum you will have many opinions.

John from PA