Practical Solutions to Machinery and Maintenance Vibration Problems
Chapter 8, Vibration in Bearings
Section 4, Importance of Pickup Mounting and Location
In order to accurately monitor and trend IBF units over time, it is necessary to acquire accurate readings. Of all the various vibration units available, IBF units are the most sensitive to pickup location and mounting techniques. Small changes in location and/or mounting techniques can give rise to large changes in IBF amplitude readings, making it very difficult to identify the genuine changes in IBF number. The preferred location is as physically close to the bearing as possible and preferably (but not essentially) in the "load zone." For the usual vibration units, such as velocity or displacement, having one to a few interfaces between the pickup location and the bearing itself is not very important. However, for IBF measurements, each interface decreases the accuracy of the reading. Therefore, try to choose a location with the least amount of interfaces between pickup location and the bearing. As with all maintenance work, compromises may be necessary. If so, IBF absolute numbers may have to become secondary to IBF changes from one time to another.
For initial maintenance setup on large machines, it may be necessary to review the engineering drawings in order to find an appropriate pickup location that will provide a good transmission path. The location must be clearly marked on the machine so that subsequent readings will be acquired in the same location.
Stud mounting is the best, but obviously more expensive. A practical
alternative would be the magnetic holder. Use of an extension probe
"stinger" or stem usually does not produce as good results
unless of short length and adequately tightened to the pickup. Update
also suggests small drill point holes on the case's measuring points.
This textbook contains only part of the information in our Practical Solutions seminar.