Fluke 281 User Manual page 255

waveform sync. Pressing the done soft key on this screen returns the display to the
STANDARD WAVEFORMS screen.
The means by which pulse period is set-up in the hardware requires an understanding
because it affects the setting resolution of both pulse width and delay. Pulse is actually a
particular form of arbitrary waveform made up of between 4 and 100,000 points; each
point has a minimum duration of 10·000000 nscorresponding to the fastest clock
frequency of 100 MHz.
At short pulse periods, i.e. only a few points in the waveform, the period setting
resolution is, however, much better than 10·000000 ns because the time-per-point is
adjusted as well as the number of points; since the pulse width and delay are also defined
in terms of the same point time, varying the time-per-point affects their resolution. For
example, if the period is set to 200.00000 ns, the minimum pulse width, when set to
10·000000 ns, will actually be 10·000000 ns; 20 points at 10·000000 ns each exactly
define the 200.00000 ns period. However, if the period is set to 199·00000 ns, 20 points
at the minimum point time of 10·000000 ns will be too long so 19 points are used and the
point time is adjusted to 10.473684 ns (199·0÷19); 10.473654 ns is now the increment
size used when changing the pulse width and delay.
For periods above 1 ms the maximum number of points in the waveform (100,000)
becomes the factor determining pulse width and delay resolution. For example, with the
period set to 100 ms, the smallest pulse width and delay increment is 1 µs
(100 ms÷100,000). This may appear to cause significant errors at extreme settings (e.g.
setting 10 ns in the above example will still give an actual width of 1 µs) but in practical
terms a 1 in 100,000 resolution (0·001 %) is quite acceptable.
Pulse period can be adjusted irrespective of the pulse width and delay setting (for
example, it can be set smaller than the programmed pulse width) because, unlike a
conventional pulse generator, pulse width and delay are adjusted proportionally as the
period is changed. For example, if, from the default pulse settings of 100 µs period and
50 µs width, the period is changed to 60 µs the pulse width actual changes to 30 µs
even though the program width is still 50 µs; to get a 50 µs width with the period at
60 µs the width must be re-entered as 50 µs after the period has been changed.
Period can also be changed from the PULSE PERIOD screen called by pressing the
FREQ key with pulse mode selected.
The new setting can be entered either as a period in the way already described or as a
frequency by first pressing the freq soft key. However, changing the period or
frequency from this screen is slightly different from changing period on the pulse set-up
screen. When changing from this screen the number of points in the waveform is never
changed (just as with a true arb) which means that the shortest period (highest repetition
frequency) that can be set is the number of waveform points multiplied by 10·00 ns. To
achieve faster frequencies (up to the specification limit) the period must be changed from
the pulse set-up screen; changing the frequency from the pulse set-up screen causes the
number of points to be reduced as the period is reduced (for periods <1ms).
Because pulse waveforms are actually a particular form of arb and use clock synthesis
mode, pulse mode can also be operated with an external clock connected to the rear panel
PULSE PERIOD: int
100·00000 us
freq period
Pulse and Pulse-trains
Pulse Set-Up
10
10-3