CEMB USA N300 - Manual (Page 35)

Balancing function 6 - 1
Chapter 6
Balancing function
One of the most frequent causes of vibration is an unbalanced rotating body (unevenness
of the mass around its rotation axis), which can be corrected by balancing.
The N300 instrument can be used to field balance any type of rotating body, on one or two
planes, using 1 or 2 vibration detectors and a photocell.
All of the situations are covered by ad hoc procedures guiding the operator step-by-step
through the sequence of operations.
In practice, the most frequent goal is to reduce vibration to an acceptable goal below a
certain value (see Appendix B). However reducing the unbalance only has an effect on the
synchronous component 1xRPM. If this component has a low value, accompanied by a
high Overall value, it indicates problems not connected with unbalance and that cannot
therefore be corrected by balancing (see Appendix C).
A preliminary analysis must therefore be carried out to assess the entity and cause of
vibration before proceeding with balancing: the N300’s vibrometer function can be used to
take an overall vibration measurement (Overall) and a synchronous value measurement
1xRPM (see chapter 5 –Vibrometer Function). Only proceed with balancing if the latter
is predominant; otherwise it is best to concentrate on resolving other problems with the
machine.
The following instructions must be complied with for correct balancing:
- position the sensors as close as possible to the supports of the rotating body to be
balanced, using the magnetic base or fixing it with a threaded hole for good
repeatability;
- apply a suitable reflecting sticker on the rotating body as a point of reference (0°).
Starting from this position, the corners are measured in the opposite direction
compared to that of the shaft’s rotation.
− connect the photocell to the N300 instrument and position it at a distance of
between 50 and 400 mm from the rotating body. Slowly turn the rotating body (if
possible by hand, otherwise as slowly as possible) and check that the LED
positioned on the back of the photocell only lights up once per turn, when the ray
of light lights up the reference mark. If that is not the case, move the photocell
closer to or further away from the piece or tilt it away from the surface.