BNC 645 - Manual (Page 158)

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the duty cycle deviation. If one is held constant, the other specified in the
command will be automatically converted to the equivalent value.
PWM:DEViation? [MINimum|MAXimum]
Query the pulse width deviation. The pulse width deviation is seconds will be
returned.
PWM:DEViation:DCYCle {< deviation in
percent>|MINimum|MAXimum}
Specify the duty cycle deviation in percent. This value represents the duty cycle
variation in the modulated waveform from the duty cycle in the original pulse
waveform, and it is in the form of a percentage of the period.
The default duty cycle deviation is 1%, and the range is from 0% to 100%. The
minimum value is 0% and the maximum value is approximately 100% (limited
by the period, minimum pulse width, and edge time). More over, it must not be
greater than the pulse duty cycle and is under the following constraints:
Duty Cycle Deviation ≤ Duty Cycle – 100 Χ Minimum Width/Period
And
Duty Cycle Deviation≤ 100 – Duty Cycle – 100 Χ Minimum Width/Period
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.
The duty cycle deviation also needs to conform to the following rules:
Duty Cycle Deviation≤Duty Cycle-(160Χ Edge Time)/Period
And
Duty Cycle Deviation≤100-Duty Cycle-(160Χ Edge Time)/Period
When you choose an external source (PWM:SOUR EXT), the duty cycle 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