User Manual

3.10 FFT Analysis Modes
100
Waveform Example
The coherence function has two general definition formulas. For the definition formulas, see "3.10.2 Analysis
Mode Functions" (⇒ p. 102)
Coherence Function COH
This function gives a measure of the correlation (coherence) between input and output signals. Val-
ues obtained are between 0 and 1.
With a single measurement, the coherence function gives a value of one for all frequencies. Spectrum
(frequency-domain) averaging should always be performed before measurement (analysis is not
available with time-domain averaging).
Main uses:
• To evaluate transfer functions
• In a system with multiple inputs, to inspect the effect of each input on the output
See About the Functions "3.10.2 Analysis Mode Functions" (⇒ p. 102)
Axis Display Type Description
X axis
Linear
Frequency is displayed with equal spacing
Display Range: DC to the top of the frequency range
Log
Frequency is displayed logarithmically
Display Range: 1/400
th
to 1/4000
th
(depending on the number of analysis
points) to the top of the frequency range
Y axis Lin-Mag
Displays the causal relationship and degree of relationship between two input
signals, as a value between 0 and 1 (dimensionless units).
Normal display
X axis: Log
Y axis: Lin-Mag