Novanta f201, Руководство пользователя

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CONTROLLING LASER POWER PAGE | 57
Pulse width modulation (PWM)
Pulse Width Modulation, or PWM, controls laser power by varying the duty cycle of F201 laser’s RF amplifi-
ers, which in turn control the time-averaged RF power applied to the laser. Typically, laser output follows
the PWM input with a rise and fall time constant of ~150
μ
s; however, the laser cannot precisely follow
PWM input signals if the “On” pulse is less than 150
μ
s in duration. At a constant 50% duty cycle, f201 lasers
typically reach 90–100% of full optical output when operated at a frequency of 3 kHz.
The percentage of optical output increases as duty cycle increases (at a constant PWM frequency) or as
PWM frequency decreases (at a constant duty cycle). Figure on the following page shows representative
f201 optical output waveforms at two different duty cycles and frequencies.
Figure 4-3 Typical F201 laser f201 waveforms.
f201 lasers are designed to operate at Command signal base frequencies up to 100 kHz; however, the
choice of PWM frequency depends on the user’s specific application. In the majority of laser applications,
the UC-2000’s default Command signal frequency of 5 kHz has proven to work well. When considering
Command frequencies at 5 kHz or below, please review Marking/engraving operation later in this section.
For high-speed motion applications that cannot tolerate any ripple in the optical beam response but still
need adjustable power levels, we recommend the use of higher PWM frequencies, up to 100 kHz maximum.
At 100 kHz, the laser’s optical beam response no longer follows the Command input and is very nearly a
DC value with just a small amount of ripple present.
Warning: Serious Personal Injury
Because of phase differences, external tickle pulses may combine with the internally-generated tickle
signal causing the Lase LED to flicker during the transition from tickle to lasing. Laser output may
occur if the Lase LED flickers.