Digital Storage Oscilloscope 20
point on the left edge of the screen). Turn the VERTICAL POSITION knob clockwise to
move up the spectrum.
2.7.2.7 Using Cursors to Measure FFT Spectrum
You may use cursors to take two measurements on the FFT spectrum: amplitude (in dB)
and frequency (in Hz). Amplitude is referenced to 0db that equals 1VRMS here. You
may use cursors to measure at any zoom factor.
Push the CURSOR button, choose the Source option and then select Math. Press the
Type option button to select between Amplitude and Frequency. Click the SELECT
CURSOR option to choose a cursor. Then use the V0 knobs to move Cursor S and
Cursor E. Use the horizontal cursor to measure the amplitude and the vertical cursor to
measure the frequency. Now the display at the DELTA menu is just the measured value,
and the values at Cursor S and Cursor E.
Delta is the absolute value of Cursor S minus Cursor E.
2.8 Trigger System
The trigger determines when the oscilloscope begins to acquire data and display a
waveform. Once a trigger is properly set up, the oscilloscope can convert unstable
displays or blank screens to meaningful waveforms. Here introduce some basic
concepts about trigger.
Trigger Source:
The trigger can be generated with multiple sources. The most
common one is the input channel (alternative between CH1~CH4). Whether the input
signal is displayed or not, it can trigger normal operations. Also the trigger source can
be any signal connected to an external trigger channel or the AC power line (only for
Edge triggers). The source with the AC power line shows the frequency relationship
between the signal and the AC commercial power.
Trigger Mode:
You can select the Auto or Normal mode to define how the oscilloscope
acquires data when it does not detect a trigger condition. Auto Mode performs the
acquisition freely in absence of valid trigger. It allows the generation of untriggered
waveforms with the time base set to 80ms/div or slower. Normal Mode updates the
displayed waveforms only when the oscilloscope detects a valid trigger condition.
