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Reply with quote  #16 
Dear Oli and MarkL
Thanks for the insighful replies.Let me digest it firsy

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Posts: 1,120
Reply with quote  #17 
Electric Pete had a good piece on it on the old forum I came across it this morning whilst looking for something else.

No, it would not be appropriate to use that chart to interpret gE. 

gE is a highly processed form of acceleration used to evaluate bearing defects. The relationship to actual acceleration is unknown (without careful study of the actual waveform). The overall gE could be higher or lower than the overall acceleration. The primary value of gE would be trending/comparison, or using limits developed by someone who used similar processing and mounting to you. 

The Rathbone chart you presented primarily applies to low (below 1000cpm) and middle (1000cpm-20,000cpm) frequencies such as would come from unbalance/misalignment/looseness. To have a prayer of catching bearing defects (which is not really a job for overall anyway), for higher frequencies (above 20,000), the chart should slope down again. You'll find many more recent charts such as NEMA MG1 limits have similar curve, except the velocity limit decreases at high frequencies above 20,000. 

I'm not trying to be negative, but trying to pretend that gE overall represents acceleration and then reading off this chart would be completely misleading and incorrect. The only thing you can do with gE overall is trend/compare.

Link to rest of the article for context.

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