Fluke PM6690 Operator's Manual page 74

Measurement Control
scribed first does not employ arming at all but
rather draws on the fact that a counter of this
type tends to self-synchronize its internal pro-
cesses to the input signal.
Our task is to synchronize the start of the mea-
surement (start trigger) to the leading edge of
the first pulse. Depending on the signal tim-
ing, this can be easy, difficult, or very diffi-
cult.
n
A. Auto Synchronization Without
Arming
If we are lucky, we can manage without using
the arming function at all. Often, the counter
can automatically synchronize the measure-
ment start to the triggering of the first pulse.
The conditions for success are that the PRF is
not too high, preferably below 50 Hz and cer-
tainly not above 150 Hz. The duration of a
pulse burst (between first and last pulse)
should be substantially less than the distance
to the next burst, and the number of pulses in
the burst should be more than 100 to avoid oc-
casional miscounts.
Do the following steps to perform auto syn-
chronization without arming:
–
Connect the burst signal to input A.
–
Adjust the manual sensitivity and trigger
level until the burst signal triggers the
counter correctly.
–
Use the MEAS/FUNC key to select
Pulse Width A.
–
Use Pacing Time to select a value that
approaches the time between the bursts.
Absolute synchronization will not be guaran-
teed in this way, but there is a high probability
that auto-synchronization will work anyway.
However, occasional erroneous values will be
displayed. To achieve guaranteed synchroni-
zation, use the Start Arming function.
5-10 Arming Examples
n
B. Synchronization Using Start
Arming
The SYNC signal can be directly used to arm
the measurement. This requires that the lead-
ing edge of the SYNC signal occurs more than
5 nanoseconds before the leading edge of the
first pulse in the burst. See Fig. 5-9.
S y n c E S t a r t A r m i n g
I n p u t A
> 5 n s
Fig. 5-9 Synchronization using start arm-
ing.
Do the following steps to perform synchroni-
zation using start arming:
–
Connect SYNC to input E.
–
Connect the burst signal to input A.
–
Adjust the trigger level to match the burst
signal under study.
Press SETTINGS ® Arm
–
–
Select Start Arm Delay = 0 and Start
Chan E.
–
Use MEAS/FUNC to select
Pulse Width A.
If there is no (or too little) time difference be-
tween the arming signal and the first pulse in
the pulse burst, arming must be combined
with a delay. See example C.
n
C. Synchronization Using Start
Arming With Time Delay
If the pulse bursts have a stable repetition fre-
quency, you synchronize the measurement us-
ing Start Arming with Time Delay. Here you
use the SYNC pulse belonging to a preceding
burst to synchronize the start of measurement.