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Displaying the Frequency Spectrum
By default, MultiView displays time-domain data: vibration readings over time. You can also have MultiView
display frequency-domain data: the frequency spectrum determined by a Fast Fourier Transform (FFT) of the time-
domain data. As shown in the figure below, when displaying a frequency spectrum, MultiView divides the trace
area, showing the vibration traces on the right, and the frequency spectrum on the left.
In the frequency-spectrum display, the horizontal axis is the vibration frequency, and the vertical axis displays the
amplitude for that frequency. Both scales are linear. Frequencies are limited to 200 Hz and below, by the AMS.
Each frequency display has a vertical green line. The line is positioned at a particular frequency (100 Hz, by
default), and the text at the top of the line identifies the frequency and the current amplitude for that frequency.
You can move the lines to monitor the amplitude at different frequencies.
By default, MultiView performs the frequency analysis using a sample of 512 data points (512 milliseconds of
data). MultiView receives data from the AMS in packets of 100 data points. The FFT is computed every 100
milliseconds, using the latest packet of 100 points, plus the previous 412 data points. You can specify a different
sample size. Increasing the sample size increases the resolution of the frequency spectrum, but the additional data
points cause the FFT results to respond more slowly to changes, similar to the way a rolling average tends to
smooth out changes. When you change the FFT sample size, MultiView automatically disables all trigger and
Go/No-Go tolerance
s. After changing the sample size, you’ll need to adjust and
re-enable any triggers or Go/No-Go
tolerances.
Frequency spectra
Vibration traces
