Measurement Time And Rates; What Is Arming - Fluke PM6690 Operator's Manual

99999999, and the quantization error is worst
case. The best case is when the displayed
value is 10000000. Then the quantization res-
olution corresponds to ± 0.5 LSD units.
+
± 1 unit in 99999999 (=1E8)
means 10 times more relative
resolution than ± 1 unit in
10000000 (=1E7), despite the
same number of digits.
A gradual increase of the measurement time
reduces the instability in the LSD caused by
the quantization uncertainty. At a specific
measurement time setting, the counter is justi-
fied to display one more digit. That one addi-
tional digit suddenly gives ten times more dis-
play resolution, but not a ten times less
quantization uncertainty. Consequently, a
measurement time that gives just one more
display digit shows more visual uncertainty in
the last digit.
For a stable LSD readout, the maximum mea-
surement time selected should be one that still
gives the required number of digits. Such opti-
mization of the measurement time enables the
total resolution to be equal to the quantization
resolution.
Measurement Time and
Rates
The set measurement time decides the length
of a measurement if Frequency or Period
Average is selected.
This is important to know when you want to
make fast measurements, for example when
you are using the statistics features, or when
you are collecting data over the GPIB bus.
The so-called "dead time", that is the time be-
tween the stop of one measurement and the
start of the next one in the course of a block
measurement, can be below 2 ms.
Measurement Control
A block is a collection of consecutive mea-
surements, the results of which are stored in
local memory for statistics or plotting pur-
poses (STAT/PLOT menu) or for later trans-
fer to a controller over one of the data com-
munication links (GPIB, USB or
ETHERNET).
Additional controls over start and stop
of measurements
Free-running measurements may be easy to
understand, but measurements can get more
complex.
Besides input signal triggering, the start of a
measurement is further controlled by the fol-
lowing elements:
–
Manual RESTART, if HOLD is selected.
–
GPIB triggering (<GET> or *TRG), if bus
triggering is selected.
–
External arming signal, if Start Arming
is selected.
–
Expired start arming delay, if Arming
Delay is selected.
In addition to expired measurement time and
stop signal triggering, the stop of measure-
ment is further controlled by:
–
External arming signal triggering, if Stop
Arming is selected.
GPIB triggering is described in the Program-
ming manual.
Now let's look deeper into the concept of
arming.

What is Arming?

Arming is a pretrigger condition ("qualifier")
that must be fulfilled before the counter al-
lows a measurement to start.
Arming can also be used to qualify the stop of
a measurement. This is called "stop arming"
The Measurement Process 5-5