Process
Basic Free-running Measurements
Since these counters use the reciprocal count-
ing technique, they always synchronize the
sta
rt and stop of the actual measuring
period to the input signal trigger events. A
new mea- surement automatically starts when
the previ- ous measurement is finished
(unless
HOLD is on). This is ideal for
continuous wave signals.
The start of a measurement takes place
when the following conditions have been
met (in order):
The counter has fully processed the previ-
All preparations for a new measurement
are made.
The input signal triggers the counter's
measuring input.
The measurement ends when the input signal
meets the stop trigger conditions. That hap-
pens directly after the following events:
The set measurement time has expired (ap-
plies to Frequency and Period Average
measurements only).
The input signal fulfils the stop trigger
conditions, normally when it passes the
trigger window the second time.
Resolution as Function of
The quantization error and the number of dig-
its on the display mainly define the resolution
of the counter, that is the least-significant digit
displayed.
As explained on page 4-10 under
Reciprocal Counting, the calculated
frequency f is:
while the relative rms quantization error Eq =
+100ps/tg.
The counter truncates irrelevant digits so that
the rms quantization resolution cannot change
the LSD (least-significant digit) more than 5
units. This occurs when the displayed value is
99999999, and the quantization error is worst
USER MANUAL ● CNT 9x Series ● Rev.22 February 2020
5-4
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