Agilent Technologies InfiniiVision 7000B Series Guide de l'utilisateur Page 200

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6 Measurements and Math Functions
200 InfiniiVision Oscilloscopes User’s Guide
The measured frequency is normally displayed in 5 digits, but can be displayed in 8 digits
when an external 10 MHz frequency reference is provided at the 10 MHz REF rear panel
BNC and the gate time is 1 second (50 ms/div sweep speed or greater). See (“To supply
a sample clock to the oscilloscope” on page 406.)
The hardware counter uses the trigger comparator output. Therefore, the counted
channel’s trigger level (or threshold for digital channels) must be set correctly. The Y
cursor shows the threshold level used in the measurement.
Any channel except Math can be selected as the source.
Only one Counter measurement can be displayed at a time.
Duty Cycle
The duty cycle of a repetitive pulse train is the ratio of the positive pulse width to the
period, expressed as a percentage. The X cursors show the time period being measured.
The Y cursor shows the middle threshold point.
Frequency
Frequency is defined as 1/Period. Period is defined as the time between the middle
threshold crossings of two consecutive, like-polarity edges. A middle threshold crossing
must also travel through the lower and upper threshold levels which eliminates runt
pulses. The X cursors show what portion of the waveform is being measured. The Y
cursor shows the middle threshold point.
To isolate an event for frequency measurement The following figure shows how to
use Zoom mode to isolate an event for a frequency measurement. If the measurement is
not possible in the Zoom mode, then the normal time base is used. If the waveform is
clipped, it may not be possible to make the measurement.
Duty cycle =
+ Width
Period
-------------------
X 100
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