The setting of alarm levels plays a vital role in a machinery condition monitoring and diagnostic system. Two approaches to set vibration alarm levels using vibration signals produced by shipboard fire pumps are presented for the time and frequency domains. In the time domain, cross peak analysis (CPA) is proposed to extract the dominate peak points. The distribution of these cross peak points is found to have a lognormal distribution and can be normalized to a Normal distribution in the VdB domain. The computed μ+2σ value in the VdB domain is the suggested alarm level. In the frequency domain, 1/1 octave band analysis (OBA) is introduced. An artificial fault simulation was conducted to compare 1/1 OBA with the broadband method. The result shows that 1/1 OBA is more sensitive to changes in VdB level than the broadband method.
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