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2.2.2 Roller Bearing Analysis
The VIB-I/O module uses the shock pulse method to analyze the roller
bearing. This method provides the measurement of mechanical shock
impulses. They arise during operation from the contact between the roller
bearings and the rolling path in the load zone and spread in waves in the
material. The signals measured during the rolling process divide in the carpet
value and the peak value. With increasing deterioration of the measuring state,
the distance between those two values will increase. The VIB-I/O module
measures the carpet value, as well as the peak value. With the analysis of these
two parameters, damages can be detected very early. Shock impulses are
influenced by the rolling speed of the roller bearings.
The subsequently used scale in three parts for the evaluation of the roller
bearing state ('good', 'limited' and 'poor') shall serve only as a pictorial
example. The actual limits boundaries between 'good', 'limited' and 'poor'
roller bearing condition can differ strongly from bearing to bearing, depending
on the design and operational conditions. A reliable diagnosis of a bearing
condition is only possible with a trend analysis over longer periods of time.
2.2.3 Shock Impulses
Shock impulses are momentary impulses arising from mechanical damages to
roller bearings or the bearing surfaces. The severity of these shock impulses
depends, amongst others, from the rolling speed of the roller bearings. Shock
impulses occur during machine operation as frequently as vibrations. They can
be traced to various causes, e.g., shocks due to harsh handling or explosions.
The deciding factor is their short duration. A shock impulse may be defined,
as e.g., transmission of kinetic energy to a system in a relative short time.
Shock impulses occur in bearings. There, they are caused by the contact
between the roller bearings and the rolling path of the load zone. Because
both, the surface of the rolling path and the surface of the roller bearing are
rough, signals are generated by the collision at locations where the lubricant
layer is not thick enough and these roughness peaks meet. These signals
spread in waves and are transmitted to all other surrounding parts via the
bearing.
2.2.3.1 Measuring Shock Impulses
The acceleration sensor mounted to the load zone of the bearing is actuated
through shock impulses at its natural resonance of approx. 30 kHz. A high
band filter is used to suppress low frequency portions, - such as those caused
by alignment or balancing errors. The remaining signal portions are processed
by the computer to obtain various shock impulse parameters that are described
in the following pages.
WAGO-I/O-SYSTEM 750
I/O-Modules
Machine Condition Monitoring with VIB-I/O Modules
Condition Monitoring
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