X90 mobile modules
X90 mobile system User's manual V 1.20 - Translation of the original manual
253
Operator's limits - Experience-based values
Operators can also draw on their own experience when assessing the status of the machine. Long-term observation
of the characteristic values and the machine's history can provide relevant values based on experience.
The limits ascertained from this can vary significantly from limits set by norms and those prescribed by the man-
ufacturer of the machines. This assessment is only possible when operators have considerable experience with
oscillations in the machine and are in a position to differentiate between positive and negative characteristics.
When determining limit values, it is important to note that vibration measurements are influenced by factors such as:
•
The location of the damage
•
The location of the sensor
•
The speed of the moving parts of the machine
•
The load on the machine parts
Assessing the trend
In many cases, not enough is known about the actual behavior of a machine during operation, in particular when
there is damage.
To make a reliable statement about its condition, the chronological sequence of the characteristic values (charac-
teristic value trend) must also be used when making the assessment.
In the progression of the trend, the "Normal condition" is the starting point. The reference level (normal level) is
the level of the characteristic value as set in the normal condition.
Changes in the trend are observed with the normal condition as the starting point. When there is damage, the
relevant characteristic values in each case generally increase, although a decrease can also be an indication of
a problem in the system.
In order to assess trends accurately, it is essential that the characteristic values of the oscillations are always
recorded under the same operating conditions and always classified in the same way. In particular, the speed and
load ratio have a strong effect on the characteristic values. Increases in trends under differing operating conditions
cannot necessarily be a sign of a change in the actual condition. In many cases, trend observation can assist in
monitoring the condition of the machine and bearings.
27.01
16.02
04.03
24.04
13.05
01.06
5
10
15
20
25
30
35
40
45
rms
[mg]
Time
Failure
Figure 86: Typical trend progression
The first and second derivatives of the damage progression trend line can provide good information about how
badly a component is damaged.
Example
This example will use the first and second derivative to determine the best time for repairs. The maximum service
life will be taken into account when selecting a time to perform a replacement. The possibility of lowered production
quality is not taken into consideration.
