VMI VIBER X5 MKIII, Инструкция по эксплуатации инструмента

Страница: 104 / 121

104
8.9. Residual unbalance
What is a residual unbalance?
If we place a large weight in the shaft centre we do not get an unbalance. The radius from
the shaft centre is also important.
The residual unbalance in VIBER X5 MkII™ is always the product of the unbalance weight
times the radius and has often the unit gram/mm = gram millimeter.
That is why the numbers in the residual and allowable unbalance seams so large.
A residual unbalance of 100 grams corresponds to an unbalance weight of:
1 gram at the radius 100 mm or 10 grams at the radius 10mm or 100 grams at the radius
1mm.
They all produce the same centrifugal force and unbalance vibration.
8.10. Response matrix
VIBER X5 MkII™ calculates and stores the unbalance sensitivity ( Response Matrix ) while you
are balancing. Next time you want to balance the same machine you can use the response
matrix and the instrument calculates the balancing weights directly after the first trial run,
or if all transducers are already mounted, even while the machine is still in production. No
trial weights are needed to be mounted.
When you use the Response Matrix all transducers including the RPM transducer must be
placed in the same directions and locations as when the Response Matrix was first
calculated.
What is a response matrix?
When we mount a trial weight in the machine and make a new start the vibrations have
changed. (If they have not changed the trial weight is too small). We can calculate this
change by (vectors) subtracting the vibrations without the trial weight from the vibrations
with the trial weight.
If we divide this change in vibration with the weight of the trial weight we will get the
normalised unbalance sensitivity or the response matrix.
For example:
The change in vibration is 8 mm/s caused by a trial weight of 50 grams on the radius 400
mm. Then the unbalance sensitivity will be 8/(50x400) = 0.0004 or 4.0E-4 (mm/s) / (gram
millimeter). This value is called a11=0.004 in the response matrix.
The unbalance sensitivity can be explained in other words. First, we assume that the
machine in our example has no unbalance what so ever thus the vibration is zero (0).
If we mount a weight of 1 gram on the radius 1 mm = 1 gram millimeter, then the vibration
would be 0.0004 mm/s.
If we mount this weight in the direction we call zero (0) degree in the machine and the