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Chapter 5, FRONT PANEL OPERATION
be updated.
LIVE FFT
When the
key adjacent to the Live FFT control is pressed, the instrument
acquires data repeatedly, performs an FFT on it and displays the resulting spectrum
until the Stop key is pressed.
NOTE: Live data acquisition is not available at 0.2 kHz and 0.4 kHz measurement
resolutions.
Cursor
The
and
cursor movement keys move the display cursor from side to side. The
cursor takes the form of a short vertical line that is positioned just above the top of
the data curve at the selected frequency, which appears just below the X-axis. In
figure 5-29 the cursor can be seen positioned at 55.0 kHz. The cursor makes it
possible to obtain an approximate frequency for any peak on the display, thereby
possibly assisting in identifying its source.
Reference Frequency Indicator
The display shows the letter "R" centered above the frequency at which the lock-in's
reference channel is currently operating. This makes it possible to quickly identify
the signal of interest from all the other signals present.
Using the Spectral Display Mode
In a typical experiment, if the lock-in amplifier's output is more noisy than might be
expected with the given settings, then the spectrum of the total input signal being
measured can be determined and displayed using the Spectral Display menu. If
strong interfering signals close to the reference frequency are observed, then the
reference frequency should if possible be changed so that operation occurs in a
quieter region. Alternatively it may be possible to switch off the source of the
interference, which might for example be caused by a switched mode power supply
used to power another item of test equipment.
Pressing the Previous Menu key exits the Spectral Display menu and returns to
Main Menu 1.
5.3.24 Main Menu 2
When Main Menu 1 is displayed, pressing the Main menu 2 key accesses
Main Menu 2, which is shown in figure 5-30.
5-39
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