Tach Trigger; Averaging; Average Overlap; Explaining Waveform Parameters - Commtest Instruments vbBalancer Instrument Reference Manual

Tach Trigger

When you select Tach Trigger, measuring begins only when a
tachometer pulse is detected. If Tach Trigger is set to OFF the
instrument will begin measuring as soon as the settling time has
elapsed.

Averaging

When measuring vibration, several spectra are usually measured
and averaged to produce an average vibration chart. The averaging
process minimizes the effect of random variations or noise spikes
that are inherent in vibration signals. Averaging is applied to
amplitude values, not to the frequency range.

Average Overlap

Overlapping is a means of collecting and displaying data more
quickly. As vibration measurements are collected a percentage of the
new data is combined (overlapped) with each subsequent
measurement. The higher the overlap percentage, the less newly
acquired data is needed to generate a spectrum, and thus the faster
the spectrum can be displayed. An overlap percentage of 50% is
ideal for most cases.

Explaining Waveform Parameters

Equivalent Fmax

This allows you to control the waveform sampling rate by expressing
it in terms of the maximum frequency of interest. For example, if you
want a waveform with frequency content (Equivalent Fmax) up to 1
kHz, the instrument will automatically sample at 2.56 kHz. Changing
the Eq. Fmax directly affects the sampling rate, so it has an inverse
effect on the duration of the waveform.

Number of Samples

The resolution of the waveform increases with the number of
samples used i.e. the more samples, the more information the
waveform contains. However, the more samples in a waveform, the
more memory is used up to store the waveform.
80 Section 7: Setting Measurement Options