VMI VIBER X5 MKIII, Instrument Manual, Page: 43 / 121

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5.1.8. Averaging
(Linear, Exponential, Smart, Peak Hold)
Averaging means that the different parts are averaged together, and can be used for
reducing random errors like background vibration due to a source other than the machine
being measured.
Linear means that each part spectra/value has the same weight in the final spectra/value.
If we for example select 8 as the No of Averages, every line level in the spectra will be
divided by 8. When all the parts of the spectra are summed the level of each line is an
average of the 8 measurements. This type of average will enhance continuous signals and
reduce noise and stochastic signals. Linear averaging is well suited for trend analysis and
most other frequency analysis. The measurement stops automatically when all the part
spectra have been measured.
Exponential means that the last part spectra/value has the same weight in the final
spectrum/value as the sum of all previously measured parts.
A sudden change in the vibration level is more visible than with the other averages.
Exponential is used when you want to see the variations in the vibration signal.
The measurement stops automatically when all the parts have been measured.
Smart averaging is similar to linear averaging with one difference:
If the value changes more than 5% percent the averaging resets.
The advantage is that when you move the transducer from one location to another, the
movement of the transducer will generate a high value. On linear averaging, if the No of
Averages is high, this will cause the value to slowly change to actual value during a long
time. This is also the case when the measurement condition (as speed) changes.
Peak Hold means that the largest value of each spectrum line is stored in the final spectra.
If the level at the 50 Hz line is largest in the part spectrum 2, and the 200Hz line is largest
in part spectrum 7, both will be saved in the final spectrum.
Peak hold is used at coast up/downs or when you want to measure an unexpected event.
5.1.9. Number of Averages
(1, 2, 4, 8, 16, 32 or 64)
To get a representative measurement of the vibrations in a machine we must measure the
vibrations during a certain time. We cannot decide to stop a machine or a whole plant
based on a measurement taken during less than a few seconds.
One way to extend the measuring time is to measure several spectra during a longer time
and calculate an average spectrum. Each of these single spectra is called a measurement.