When the response input level is severely overloading, the analyzer’s input is
clipped. This results in a poor frequency response and poor coherence because
the actual response is not being measured. This is called over-ranging. See
figure 2-4.
Figure 2-4
Input Over Ranging
You should also verify that the signals are the type you expect. With a random
signal, you should measure the histogram to verify that it has a Gaussian
distribution. See figure 2-5. In addition, you can visually inspect transient
signals. See figure 2-6.
Figure 2-5.
Verify Random Test Signals
Figure 2-6.
Verify Transient Test Signals
Histogram
Random Noise
Typical Force
Exponential Decaying
Responce
Agilent 35670A
Operator's Guide Measuring Structures
2-5
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