Section 5 — Set Measurement Options119Number of AveragesThe larger the number of spectra used for averaging, the more any noisespikes in vibration signals are reduced, and the more accurately truespectral peaks are represented. However, the larger the number ofaverages, the more data needs to be collected, and the longer it will taketo obtain the average spectrum.Four averages are sufficient in most cases. You can set the number ofaverages to one if spectra averaging is NOT required (e.g. with run-upand coast-down recordings).Averaging TypesThe following averaging types are available:• Linear averaging — This is suitable in most cases. Theamplitude value at each frequency of a spectrum is added tothe same frequency of the next spectrum. The sum is thendivided by the number of averages taken.• Exponential averaging — This is occasionally used duringmanual measurements to give the advantage of a fast updaterate, while maintaining some averaging. The most recentspectra have more influence on the average than earliermeasurements. Averaging is continuous until you stop themeasurement.• Peak hold — This is useful for measuring the maximumamplitude peak that occurs over a period of time. It is alsouseful for measuring resonances during a bump test. Peak holddoes NOT average the amplitude values. It records and displaysthe maximum amplitude of each spectral line.Average OverlapOverlapping is a means of quickly collecting and displaying data. Asvibration measurements are collected, a percentage of the new data iscombined (overlapped) with each subsequent measurement. The higherthe overlap percentage, the less newly acquired data is needed togenerate a spectrum and the faster the spectrum can be displayed. Anoverlap percentage of 50% is ideal in most cases.
