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A program for evaluating any new lubrication products can be used to indicate the possible replacement of current lubricants. The general charac-teristics of new lubricants can be obtained from specifications provided by suppliers or from testing of the lubricant. The final selection of new lubri-cants should be made only after close observation of the lubricant in severaltypical plant applications. During the monthlyinspections， new lubricants should be checked especially closely to ensure they are retaining their desired properties. While all lubrication applications are important to machineryhealth， gear couplings present special critical lubrication problems and require special attention as explained previously.
Operating experience has proven that unless a continuous program ofrequired lubrication is followed， even the most well-designed units are sure to fail. A proper lubrication management program must incorporate amonthly lubrication schedule， an evaluation of new lubrication products， and supervision to ensure the prescribed procedures are carried out by maintenance personnel.
In the event of failures due to lubrication problems， the failures should be thoroughly analyzed to determine if they were indeed caused by lubricant failure or incorrect maintenance procedures. Once the problem has beenisolated， corrective action can be initiated to prevent subsequent similar failures.whether it requires changing lubricants or procedures.
Bibliography
API Standard614，""Lubrication， Shaft-Sealing and Control Oil Systems
for Special-PurposeApplications，"" American PetroleumInstitute， September
1.73.
Clapp，A.M.， ""Fundamentals of Lubricating Relating to Operating and Main-
tenance ofTurbomachinery，"" Proceedings of the 1st Turbomachinery Sympo-
sium， Texas A&MUniversity， 1.72.
Fuller，D.D.，Theory正 Practice ofLubricationfor Engineer ， WileyInterscience， 1.56.
O"Connor，J.J.， andBoyd，J.，eds.， Standard Handbook of Lubrication Engin-eering， Mc.raw-Hill BookCo.， 1.6..
16
Spectrum Analysis
A total analysis of high-speed rotating equipment requires a complex blend of performance and vibration data. The trend toward total analysis is growing with the problems of an energy shortage and the need for max-imum plant utilization. Performance analysis is essential in the efficientutilization of turbomachineryand， when coupled with vibration analysis， is an unbeatable tool as a total diagnostic system.
The real-time analyzer plays a very important role in presenting vibratory data in a manner that can lend itself to a trending data system. This important role of the spectrum analyzer will be explored in detail in thischapter. Also， the role of the spectrum analyzer will increase with a better understanding of statistical techniques in vibration analysis.
Basically， spectrum analysis transforms a displacementjtime chart into an amplitudejfrequency chart known as a spectrum. This analysis consists of decomposing a time-varying signal into its component pure tones. Pure tones are sinusoidal wave forms of constant frequency and amplitude. This decomposition is done digitally upon a signal by a minicomputer using the Fourier transformation or by filtering the signal.
Signals generated by high-speed machinery are very complex in nature and are generated by several forces with a net effect that masks the pure tones.The random portion of thesignal， which is blended with the pure tones， is called noise. The ratio of the total amplitude (area under spectrum) to that of the noise is called the signal-to-noise (SjN) ratio. Sometimes this ratio isexpressed in decibels， ordb， as follows:
S川 1 S(16-1)
N ratio in db二却 log N
558
For example:
6db二却
1 db二 3.16
却 db二 1
4 db二 1
If the SjN ratio is less than 1 db， it becomes difficult to differentiate the periodic part of the spectrum from noise.
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