Measurement Computing eZ-PostView rev.2.0 - Manual (Page 141)

eZ-Analyst 957397 Glossary G-3
Flat-Top Window, also written as Flattop Window
An FFT window function that provides accurate measurement of peak-amplitude. Compared to
the very similar 4-term “Max Flat Top,” this window also has a very low peak amplitude error,
and its frequency resolution is somewhat better. Its side lobes are considerably higher. Its
effective noise bandwidth is still almost twice that of the Hanning window, therefore this
window is used mainly to measure accurate peak amplitudes of discrete spectral components
that are known to be separated by several spectral lines.
Free Run (Free Running)
A state in which a data acquisition device acquires the next block of data when it has finished
the previous block. Free Run is a continuous collection of data, with a constant display
update.
Frequency-Domain
A domain where amplitudes are graphed in relation to frequency. Also see Time-Domain.
FRF (Frequency Response Function)
A dual-channel function for the single-input, single-output (SISO) frequency response function
between two specified input channels. FRF is the averaged cross-spectrum divided by the
averaged autospectrum of the input (the second named channel).
FSV (Full Scale Volts)
Maximum FSV refers to the high-end limit for the input voltage. Minimum FSV is the low-end
limit for the input voltage.
g
Acceleration due to gravity. In relation to earth’s gravity,
1 g = 980 cm/sec 2 , or 32.2 ft/sec 2 .
Gain
The degree to which a signal is amplified (or attenuated) to allow greater accuracy and
resolution; can be expressed as ×n or ±dB.
Hanning
An FFT window function. The Hanning window is typically used to analyze continuous signals.
The Hanning function reduces leakage and provides a relatively good compromise between
frequency resolution and amplitude accuracy.
Hz
Hertz, one cycle per second. Also, see CPM.
Impedance
Force/Velocity. A transfer type that is the reciprocal function of Receptance. Impedance is
derived by taking the inverse of the magnitude, and multiplying the phase angle by “-1.”
Inertance
Acceleration/Force. The transfer type function is calculated by dividing the cross spectrum of
the channel pair by the auto spectrum of the reference (force) channel.
Integration/Differentiation
Integration/Differentiation is for display purpose only and does not modify the data. It is only
active when frequency domain data is displayed. Select single or double integration, single or
double differentiation or none. Make your selection on the popup menu. Differentiation and
Integration are calculated by dividing each element of the function by (jw)^n, where j is the
square root of -1; w is the product of 2 pi times the frequency of the block element; and n is
an integer from +2 to -2.
n = 2 is double integration
n = 1 is single integration
n = 0 has not effect
n = -1 is single differentiation
n = -2 is double differentiation.
If the signal is acceleration, then single integration (Int1) results in velocity, and
double integration (Int2) results in displacement.
If the signal is displacement, then single differentiation (Diff1) results in velocity, and
double differentiation (Diff2) results in acceleration.