BNC 645 - Manual (Page 53)

53
Width Deviation
The width deviation represents the peak variation in the pulse width of
the modulation output based on that of the original pulse carrier
waveform. The default deviation is 10μs, and the range is from 0s to
1000s. In addition, it must not be greater than the pulse width of the
carrier waveform
and is also constrained by the following formulas:
WidthDeviation ≤ PulseWidth – Wmin
WidthDeviation≤ Period – (PulseWidth + Wmin)
where Wmin is the minimum pulse width as described in Section 4.5.
When external source is selected as the source of modulating waveform,
the modulation is controlled by the specified width deviation and the ±5v
levels of the external waveform. When the external waveform is at +5v,
the output will reach the maximum pulse width. When the external
waveform is at -5v, the output will reach the minimum pulse width.
How to set up PWM (pulse width modulation)
1. Press the Pulse button to select the pulse carrier waveform and
then set the waveform parameters as described in Section 4.5.
Figure 4-13
2. Press the Mod button to toggle the PWM output.
3. Press the softkey under Src to toggle between internal source (Int)
and external source (Ext) for selecting modulating waveform
source.
4. If internal source is selected:
a. Press the softkey under Shape to toggle between different
types of modulating waveform. If arbitrary waveform (Arb) is
selected as modulating signal source, the modulating signal
source is depending on the previous waveform selection in
arbitrary function. One may toggle the Mod key to see the
arbitrary modulating waveform message that temporarily