quency according to Mr. Hertz
measure the actual gate time (tg) and the
number of cycles (n) that occurred during this
gate time.
Thereafter, the counter calculates the fre-
's definition:
The '9X' measures the gate time, tg, with a
resolution of 100 ps, independent of the mea-
sured frequency. Consequently the use of
prescalers does not influence the quantization
error. Therefore, the relative quantization
error is: 100 ps/tg.
For a 1-second measurement time, this value
is:
Except for very low frequencies, tg and the set
measurement time are nearly identical.
If the input signal disappears during the mea-
surement, the counter will behave like a volt-
meter with a sample-and-hold feature and wi
ll
freeze the result of the previous measurement.
Mainly for GPIB use, you can manually select
a fixed time-out in the menu reached by press-
ing
SETTINGS
Misc
Timeout. The range
of the fixed time-out is 10 ms to 1000 s, and
the default setting is
Off.
Select a time that is longer than the cycle time of
the lowest frequency you are going to measure;
multiply the time by the prescaling factor of the
input channel and enter that time as time-out.
When no triggering has occurred during the
time-out, the counter will show NO SIGNAL.
The set measurement time determines the
measuring speed for those functions that uti-
lize averaging -
Frequency and Period Avg.
For continuous signals,
trigger is on and can be increased to:
when Manual trigger is on, or via GPIB:
■ Average and Single Cycle
Measurements
To reduce the actual gate time or measuring
aperture, the counters have very short mea-
s
urement times and a mode called
Single for
period measurements. The latter means that
the counter measures during only one cycle
of the input signal. In applications where the
counter uses an input channel with a
prescaler, the
Single measurement will last as
many cycles as the division factor. If you
want to measure with a very short aperture,
use an input with a low division factor.
Averaging is th
e normal mode for frequency
and period measurements when you want to
reach maximum resolution. There is always a
tradeoff between time and precision,
however, so decide how many digits you
need and use as short a measurement time as
possible to arrive at your objective.
USER MANUAL ● CNT 9x Series ● Rev.22 February 2020
4-10
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