Fluke PM6690 - Page 70

as opposed to the more common “start arm
-
ing”.
When you use arming, you disable the normal
free-run mode, i.e. individual measurements
must be preceded by a valid start arming sig
-
nal transition.
If you use start arming and stop arming to
-
gether you get an externally controlled mea
-
surement time, a so-called “External Gate”.
n
Manual Arming
The counters have a manual start arming func
-
tion called HOLD. Here you manually arm
the start of each individual measurement by
pressing the RESTART key.
Use this manual arming mode to measure sin-
gle-shot phenomena, which are either trig-
gered manually or occur at long intervals. An-
other reason for using this manual arming
could simply be to allow sufficient time to
write down individual results.
n
When Do I Use Start Arming?
Start arming is useful for measurements of fre
-
quency in signals, such as the following:
–
Single-shot events or non-cyclic signals.
–
Pulse signals where pulse width or pulse
positions can vary.
–
Signals with frequency variations versus
time (“profiling”).
–
A selected part of a complex waveform
signal.
Signal sources that generate complex wave
forms like pulsed RF, pulse bursts, TV line
signals, or sweep signals, usually also produce
a sync signal that coincides with the start of a
sweep, length of an RF burst, or the start of a
TV line. These sync signals can be used to
arm the counter. See Fig. 5-1.
n
When Do I Use Stop Arming?
You normally use stop arming together with
start arming. That means that the external
gating signal controls both the start and the
stop of the measurement. Such a gating signal
can be used to force the counter to measure
the frequency of a pulsed RF signal. Here the
position of the external gate must be inside a
burst. See Fig. 5-2.
Note that burst measurements with access to
an external sync signal are performed in the
normal Frequency mode, whereas burst
measurements without an external sync signal
are performed in the self-synchronizing Fre
-
quency Burst mode.
In time interval measurements, you can use
the stop arming signal as a sort of “external
trigger Hold Off signal.” Here you block stop
Measurement Control
5-6 The Measurement Process
S t o p A r mS t a r t A r m
E x t G a t e
B u r s t
S i g n a l
Fig. 5-2 Start and stop arming together is
used for burst signal gating.
Sync
Pulse
Si
g
nal
Fig. 5-1 A synchronization signal starts
the measurement when start
arming is used.