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Installation, operation and maintenance instructions
High voltage flameproof motors for explosive atmosphere
AMD Rg 355-400-450-500
Rolling bearings check – Impact impulses measurement
General
The bearing condition can be monitored by the
"Shock-Pulse Method".
All major bearing manufacturers know this "shock-
pulse method" and are able to offer the instrument and
give advice on request.
The principle is outlined below:
When a rolling element of a rolling bearing rolls over
any unevenness in its path it transmits so-called
shock-pulses (structure-borne noise). These shock-
pulses spread throughout the material as shock waves
and are measured as a criteria for monitoring the
bearing condition. A piezo pick-up, set at resonance
(usually at 32 kHz) is used as the sensor, its electrical
signal is then processed. The original shock-pulse is
converted in the indicating instrument to a "spike
pulse" which can then be read off as the "SV" ( =
Shock Value).
In order to evaluate the measured values they must be
multiplied by a scaling factor given by the speed and
bore diameter of the bearing in question.
The suppliers (e.g. SPM) give standard values, based
on experience, which allow a bearing to be judged as
being "good" (green), "fair" (yellow) or "bad" (red).
Extensive measurements on new bearings by various
machine manufacturers and our own experience show
that:
1. Monitoring the bearing condition is only of value if
the initial SV measurement is taken and
recorded
manufacturer's works or at commissioning; record
sheets issued by the measuring instrument
manufacturer e.g. SPM should be used and later
handed over to the customer.
during
the
running
tests
2. The initial SV measurement could already lie in the
range "fair" (yellow). However, the magnitude of
the measurement alone is not decisive at it is
influenced by many things such as bearing
roughness, kind of lubricant, installation and load
conditions.
3. After
a
certain
measurement could decrease, i.e. the bearing
condition can improve.
4. Therefore, the initial SV measurement should be
taken
as
a
measurements.
5. The informational worth of the measurements is
only given when they are taken and recorded
periodically at regular intervals.
6. Measurements must always be taken for the same
bearing conditions e.g.
- same speed, for variable speed machines.
- same load conditions, (e.g. for fans with blades
which can be adjusted during operation).
- same lubrication conditions i.e. never directly
after relubrication. The new grease must be
distributed within the bearing.
- same measuring points.
7. Based on the initial SV measurements, the
subsequent SV measurements indicate the trend
of any change in the bearing condition. This
indication of trend can be a decisive aid in planning
in
the
the next machine over-haul.
Hence, it follows that the shock-pulse method is not
suitable for bearing diagnosis based on a single
measurement only, but periodical measurements
made under the same conditions are necessary for
comparison purposes, and the differences in these
readings are the criterion for evaluation.
Sheet No.
3AAM101039 E
Rev. B
01.2023
Page 1 of 1
running-in
period,
the
SV
reference
value
for
further
Issued by: MOLM
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