Measurements and Math Functions 5
InfiniiVision 7000B Series Oscilloscopes User’s Guide 163
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 set the reference
signal mode” on page 388.)
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.
Duty cycle =
+ Width
Period
-------------------
X 100
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