Sequoia / Tahoe Series User Manual California Instruments
250 M447352-01 REV-A
FFT data displayed in bar chart format shows the same data in a graphical format; refer to Figure 7-3.
While the amplitude information is shown graphically, phase data is only displayed in numeric format at
the right-side of the display. The display could show up to 25 harmonic components at a time. The triangle
at the bottom of the display shows the currently selected component for which numeric data is shown on
the right-side. This data includes the harmonic number (DC through 50), the harmonic frequency, the
absolute or relative amplitude (depending on selection in DATA field), and the phase angle with respect to
the fundamental. The rotary encoder could be used to scroll through the displayed harmonics horizontally,
or the touch-screen could be used to directly select an individual harmonic.
Figure 7-3. FFT data in Bar Graph Format
7.3 Triggering Measurements
Both FFT results and waveform acquisitions might have to be positioned at a specific instant in time. To
allow the data acquisition to coincide with user specified events, the measurement system can be triggered
in different ways. Trigger modes are available from both the digital interface and the front panel. Refer to
the Sequoia Series Programming Manual P/N M447353-01 or Tahoe Series Programming Manual P/N
M445374-01 for details on this mode of operation.
7.3.1 Trigger Mode
Trigger mode could be selected from the front panel using the MODE field in the HARMONICS menu of
the MEASUREMENTS screen; refer to Figure 7-4.
The following trigger modes are available in the HARMONICS menu:
Single (SINGLE) This mode causes the acquisition system to be armed only once after
the initial START. The power source waits until a trigger event occurs,
after which data is acquired; when the acquisition is completed, the
system is put in an idle state. A new START must be given to trigger
a new acquisition. This mode is appropriate for capturing events that
occur only once such as the inrush current when turning on a load.
Continuous (CONT) This mode causes the trigger system to re-arm itself after each trigger
event. Every time a new trigger event occurs, new data is acquired,
and the display is updated. No user intervention is required after the
initial START. This mode is appropriate for capturing repetitive events
or the source output continuously.
7.3.2 Trigger source
Trigger sources could be selected from the front panel using the SOUR(CE) field in the HARMONICS
menu of the MEASUREMENTS screen; refer to Figure 7-4.
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