Agilent Technologies InfiniiVision 6000 Series User Manual page 244

5 Making Measurements
244
Counter
The 6000 Series oscilloscopes have an integrated hardware
frequency counter which counts the number of cycles that occur
within a period of time (known as the gate time) to measure the
frequency of a signal.
The gate time for the Counter measurement is automatically
adjusted to be 100 ms or twice the current time window,
whichever is longer, up to 1 second.
The Counter can measure frequencies up to the bandwidth of
the oscilloscope. The minimum frequency supported is 1/(2 X
gate time).
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"
page 336.)
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.
+ Width
------------------- X 100
Duty cycle =
Period
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
6000 Series Oscilloscope User's Guide
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