VMI VIBER X4, Руководство пользователя

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Vibration Measurement Instruments
Averaging (Linear, Exponential, Smart, Peak Hold)
Averaging means that the different parts are averaged together and can then be used for reducing random
errors, such as 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, for example,
you select 8 as the Number 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 for 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 the 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 mea-
surement 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%, 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 Number of Averages is high, this will cause
the value to slowly change to the actual value over a long time. This is also the case when the measurement
condition (such 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 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 for coast up or coast down, or when you want to measure an unexpected event.
Number of Averages (1, 2, 4, 8, 16, 32)
To get a representative measurement of the vibrations in a machine, the vibrations must be measured over a
certain length of time. You cannot decide to stop a machine or a whole plant based on a measurement taken
over less than a few seconds.
One way to extend the measuring time is to measure several spectra over a longer time and calculate an av-
erage spectrum. Each of these single spectra is called a measurement.
If you collect more averages, you will have fewer random errors. However, collecting more averages re-
quires more time. If, for example, you select the Number of Averages as 8, the instrument will measure 8
different spectra and continuously calculate an average spectrum. Usually 6 to 8 measurements are enough.
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