Main Menu 2 - Ametek 7280 Instruction Manual

RUN FFT
When the
acquires a new set of data, performs an FFT on it and displays the resulting spectrum.
A change in the reference frequency also causes the displayed spectrum to be
updated.
LIVE FFT
When the
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 3 kHz and 5 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 5-23 the cursor can be seen positioned at 830 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 computer monitor.
For example, in figure 5-23 the cursor has first been used to identify the strong
signals at 166 kHz, 498 kHz, 830 kHz and 1.162 MHz and then the reference
frequency has been set to 890 kHz. Finally the spectral display has been re-run to
confirm that the reference frequency is well separated from the interfering
frequencies.
Pressing the Previous Menu key exits the Spectral Display menu and returns to
Main Menu 1.

5.3.21 Main Menu 2

When Main Menu 1 is displayed, pressing the Main menu 2 key accesses Main Menu
2, which is shown in figure 5-25.
Chapter 5, FRONT PANEL OPERATION
key adjacent to the Run FFT control is pressed, the instrument
key adjacent to the Live FFT control is pressed, the instrument
5-41