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ADASH Ltd.
Adash 4400 – VA4Pro
Appendix B: ACMT bearing and gearbox
measurement
Applications
The ACMT is the brilliant tool for condition of low-speed machines like paper machines, rolling mills, transport
mechanisms... .
Description
Various processes produces short duration pulses are in slow speed machinery. Pulses are often caused by
rolling element bearings, gearbox wear, etc. It is important to be able to accurately detect and analyse these
pulses for correct diagnosis.
The individual pulse can have very short duration. Consequently it is necessary to set a high sampling
frequency for measurement. Only in this way ensures to obtain a correct measurement of signal amplitude.
The time interval between pulses can be very long when the speed is low ( seconds, minutes). We need to see
the time signal which contains several pulses as minimum for correct evaluation. The long length of time signal
is required. This matter needs to use the low sampling frequency.
These two aspects produce the conflict in the measurement setting:
1. We need to use high frequency sampling for pulse measurement, which means the measured signal will very
short e.g. 100ms. When the time interval between pulses is in seconds we have low chance to catch it. And we
have no chance to have more pulses in one time signal.
2. We need the low sampling frequency for long time record e.g. 10s to obtain more pulses in one signal. But
with such sampling we cannot measure the pulse, because cut out by anti-aliasing filter. If we switch off this
filter, we have also no chance to catch it, because pulse duration is short and time period between samples is
long.
ACMT is the solution
This method implements both contradictory requests by double sampling the data. The high sampling frequency
is used in the beginning. Then the data are compressed. That is why we can take long time signal for
evaluation.
Example
All measurements were taken on a slow-speed 23132-TOR rolling bearing rotating at 60 rpm (1 Hz). Outer race
defect is on the bearing. The short pulses are generated during the operation.
We measure the signal with a record length of 4sec. When 2048 samples (standard value) is used, then 200Hz
anti aliasing filter is used. We take the signal without any pulses. All of them are cut off by filter.
We use the 19200Hz sampling frequency. But we can measure only 42ms time signal. The time between the
pulses is 114 ms. We need to be lucky and to hit the pulse.
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