Most low-speed rotating equipments are large and important. Therefore, a plant will suffer substantial losses if the operation of such equipments stops because of any damage to their rolling-element bearings. This paper discusses a diagnostic method for rolling-element bearings in rotating equipments with extremely low speeds of 100 rpm or less and further, it proposes a diagnostic method based on acoustic emission (AE) envelope waveform of 100 kHz to 1MHz frequency. Abnormality diagnosis was performed even for a rotation number of 1 rpm by improving the signal-to-noise (S/N) ratio by carrying out further amplification after envelope waveform processing and AE waveform amplification. Furthermore, a method for removing electric noises and an abnormality-diagnosis method based on an event-counting method in the case of extremely low-speed rotation are proposed. Further, we are manufacturing a diagnostic instrument based on this diagnostic method, and we are performing abnormality diagnosis and monitoring of on-site conditions.
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