Measurement Computing eZ-Record rev.2.1 - Manual (Page 37)

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January 2001 eZ-Record Manual
Display Functions
Open Function Menu: Right click on the plot.
Using Key Commands: Press “D” + “F”. Use the arrow keys to highlight your
selection and press “Enter”. Note that in some cases you can press the first
letter of an option to select it
The data type determines the functions available for display.
Time: A single-channel display function. Displays a time domain waveform of
filtered, sampled data scaled in either Volts or EUs.
Spectrum: A dual-channel display function. Displays averaged linear spectrum
computed as the square root of the averaged autospectrum. This function is
calibrated in peak engineering units (EU).
Auto Spec: A single-channel display function. Displays the square of the
magnitude of the complex (one-side) Fourier spectrum of x(t). Autospectra
are calibrated so that if A is the peak amplitude of a sinusoidal signal x(t),
then the autospectrum has the value A
2 at the sinusoidal frequency.
PSD: A single-channel display function. It is the Fourier Transform of the
Autocorrelation function. This normalization should be used with
continuous random signals.
Coherence: A dual-channel display function. At each frequency, the
coherence is a value between 0.0 and 1.0, which indicates the degree of
consistent linear relationship between two signals during the averaging
process. A value of less than one indicates that phase cancellation occurred
during cross-spectrum averaging, which may be due to uncorrelated noise on
one or both signals or to a nonlinear relationship between signals.
FRF: 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).
Cross: A dual-channel display function in the frequency domain. It is equal to
the product of the complex Fourier spectrum of y(t) (the numerator or first
named channel) times the complex conjugate of the Fourier spectrum of x(t)
(the denominator or second named channel). The special case y=x yields the
autospectrum. Averaging of these functions (frequency-domain averaging)
forms the basic foundation on which virtually all other multichannel,