VMI VIBER X5 MKIII, Instrument Manual, Page: 95 / 121

95
Vibration before
mounting of trial
weight
Change in vibration
due to the trial
weight.
Initial
TW
8.1. Balancing Theory
When we want to balance a new machine we do not know the relationship between the
vibrations and weight e.g. how much vibration a certain weight is creating.
To solve this problem we measure the vibrations before and after we have mounted a trial
weight. If the difference in vibration between the initial run (before weight mounting) and
the trial run (after weight mounting) is 12 mm/s due to a trial weight of 43 grams then we
can calculate how many grams that are needed to change the vibration 1 mm/s.
43 𝑔𝑟𝑎𝑚𝑠
12 𝑚𝑚/𝑠
= 3.58 grams / mm/s
This is called the unbalance sensitivity of the machine and depends on the stiffness of the
machine and on the shaft speed. The VIBER X5 MkIII™ stores this unbalance sensitivity with
the name
Response matrix .
To balance a vibration of 7 mm/s we only have to multiply the vibration with the unbalance
sensitivity:
7 mm/s x 3.58 grams / mm/s = 25 grams
When we want to balance a machine where the unbalance sensitivity is unknown we must
use trial weights and trial runs.
No vibrations are completely stable. If we measure the same measuring
point twice, with a small time difference, the vibration
readings usually differ a little due to normal variation in
the vibrations, even if we are averaging the
measurement. This difference is increased if we stop
the machine between the measurements.
To minimize the effect of this “natural” variation at
balancing we must put in such a large trial weight
that the change in vibration due to the trial weight is
much larger than the natural variations.
During a trial run the instrument checks if the change in vibration is
sufficient.
8.2. Balancing Application menu
In the Balancing application menu you choose:
Ongoing = to continue the last balancing session
1 Plane = to perform a new one plane balancing
2 Plane = to perform a new two plane balancing
From File = to work with, or view, a previous balancing
session from a balancing file.
Response matrix – To perform a balancing session with the unbalance sensitivity of an
existing balancing file.
Figure 8-2: Balancing Application
Menu