Spider DSA User’s Manual
121
since the input is zero at all the DOFs other than j.
The FRF Hij can be estimated using the various classical estimators such as:
or
or
or
where GXX and GYY are the auto spectra of input and output respectively, GXY
is the cross-spectrum between input and output, and GYX is the cross-spectrum
between output and input (i.e., the complex conjugate of GXY). H1 has the
ability, by averaging, to eliminate the influence of uncorrelated noise at the
output, whereas H2 has the ability, by averaging, to eliminate the influence of
uncorrelated noise at the input. Compared to H1, H2 is less vulnerable to bias
errors at the resonance peaks caused by insufficient frequency resolution
(called resolution-bias errors).
Test Configuration
The Test Configuration window is used to set test-specific software options and
parameters. It is divided into many sections accessed by the list on the left. Many
of these sections are specific to particular test types and are described in
subsequent chapters. Other sections are for common functions shared by all test
modes. These are also described in other sections of this manual. The Test
Configuration window will be frequently referenced throughout this text.
To access these settings, go to Setup, select the Test Configuration item under
the Setup menu or click the Config button on the control panel.
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