BNC 645 - Manual (Page 157)

157
PWM:INTernal:FREQuency? [MINimum|MAXimum]
Query the internal modulating frequency in PWM. The internal modulating
frequency in hertz will be returned.
PWM:DEViation {< deviation in seconds>|MINimum|MAXimum}
Specify the pulse width deviation in seconds. Pulse width deviation represents
the variation in seconds from the pulse width of the carrier pulse width. The
range is from 0 to 1000 seconds and the default is 10μs. The pulse width
deviation cannot exceed the current pulse width. The minimum value is 0
seconds and the maximum value is determined by period, minimum pulse width
and edge time.
Here’s the constraints pulse width deviation has to conform:
Width Deviation ≤ Pulse Width – Wmin
And
Width Deviation ≤ Period - Pulse Width – Wmin
Where:
Wmin = 20 ns for period ≤ 10 s.
Wmin = 20 ns for period > 10 s, but ≤ 100 s.
Wmin = 2 μs for period > 100 s, but ≤ 1000 s.
Wmin = 20 μs for period > 1000 s.
Also
Width Deviation ≤ Pulse width – (1.6 X Edge time)
And
Width Deviation ≤ Period - Pulse width – (1.6 X Edge time)
When you choose an external source (PWM:SOUR EXT), the width deviation is
controlled by the ±5V signal level shown on the Modulation In connector on the
rear panel.
It means that when the modulating signal is at +5V, the output will
be at its maximum width deviation, and when the modulating signal is at -5V,
the output will be at its minimum duty cycle.
Lower external signal levels
produce less deviation, and negative signal levels produce negative deviation.
Note: The operation of this command is affected by FUNC:PULS:HOLD
command. FUNC:PULS:HOLD command decides if the pulse width or the duty
cycles are to be held constant as the period varies. If the pulse width is held
constant, so is the pulse width deviation; If the duty cycle is held constant, so is