Synrad 48 Series - Figure 3-7 Series 48 Waveforms

technical reference
310
Synrad
Series 48Series 48
Series 48Series 48
Series 48 operator’s manual
Controlling laser power
Pulse width modulation (PWM)
Pulse Width Modulation, or PWM, controls laser power by varying the duty cycle of the laser’s RF
amplifiers, which in turn control the time-averaged RF power applied to the laser. Because laser output
follows PWM input with a rise and fall time constant of ~100 µs, the laser cannot precisely follow
Command signal frequencies over 5 kHz with duty cycles greater than 50%. Typically, the depth of
modulation for a 50% duty cycle is 90 to 100% at 2 kHz and 60 to 80% at 5 kHz. Figure 3-7 shows Series
48 optical waveforms at two different modulation frequencies.
Figure 3-7 Series 48 waveforms
2
/
Ch2 Freq
2.008kHz
Low signal
amplitude
79 Acqs
740m V
T
Ch 1
100mV
M
100 µS
Ch 2
Ch2 +Duty
49.4%
Low signal
amplitude
1 V
Ch 2
T
500kS/sTek
step
2
/
Ch2 Freq
4.906kHz
Low signal
amplitude
500kS/s
34 Acqs
720m V
T
100mV
M
100 µS
Ch2 +Duty
50%
Low signal
amplitude
1
Ch 2
2 V
Ch 2
T
Ch 1
Tek step
2 kHz Modulation 5 kHz Modulation
1
Series 48 lasers are designed to operate at Command signal base frequencies up to 20 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 20 kHz maxi-
mum. At 20 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.
Command signal
The modulated Command signal applied to Series 48 lasers has three parameters: signal amplitude, base
frequency, and PWM duty cycle. By changing these parameters, you can command the beam to perform a
variety of marking, cutting, welding, or drilling operations.
Warning
serious
personal
injury
Always use shielded cable when connecting your PWM Command
signal source to the laser’s CTRL connections. In electrically-noisy
environments, long lengths of unshielded wire act like an antenna
and may generate enough voltage to trigger uncommanded lasing.