Novanta v40 User Manual page 54

OPERATING MODES
To operate the laser in CW mode, apply a constant +5 VDC signal to Pin 9, PWM Input, and Pin 1, PWM
Return, on the User I/O connector. This constant voltage source forces the internal switching electronics
to remain on, providing continuous and uninterrupted laser output power. During CW operation, output
power cannot be changed. To adjust output power, refer back to the Pulse width modulation (PWM)
section for information about high frequency operation
Important Note: NOVANTA lasers are designed for maximum performance at a 95% duty cycle.
Increasing the maximum PWM percentage beyond 95% greatly increases the laser's heat load with little
or no corresponding increase in laser output power. Continuous operation at 99% duty cycle may lead to
thermal instability and optical degradation.
Gated operation
In many marking and cutting applications, the laser is required to pulse, or gate, on and off in synchroni-
zation with an external control signal (typically from a computer or function generator operating in the
range from DC to 1 kHz). To pulse or gate the laser, connect a signal providing +5.0 VDC pulses to the
Gate connector on the rear panel of the UC-2000 Universal Laser Controller.
Users who intend to use a gating signal should set the UC-2000's gate input logic to internal Pull-Down
(normally off) mode. This prevents the beam from being enabled unless a high level (+3.5 V to +5.0
VDC) signal is applied to the Gate input connector. In the pull-down (normally off) mode an asserted
logic low signal, short circuit to ground, or an open or disconnected Gate input locks the beam off.
The UC-2000's default gate logic is factory set to internal Pull-Up (normally on) mode so that an
open (disconnected) Gate input causes the laser to turn on. This functionality allows the user to easily
test and verify laser operation prior to integration.
In an integrated system, you should configure the UC-2000's gate input logic to internal Pull-Down
(normally off) mode. This prevents the beam from being enabled unless a high level (+3.5 V to +5.0
VDC) signal is applied to the Gate input connector. In the Pull- Down (normally off) mode an asserted
logic low signal, short circuit to ground, or an open or disconnected Gate input locks the beam off.
Many CO2 lasers operating in applications requiring short gating pulses at repetition rates below 500 Hz
will exhibit some leading-edge overshoot regardless of the PWM frequency. This occurs because a
cooler lasing medium (the CO2 gas) is more efficient than a hotter one. The overshoot effect is more
pronounced at lower gating frequencies since the gas has a longer time to cool down between
Command signal pulses.
Marking/engraving operation
When the delay between the end of one PWM Command signal pulse and the beginning of the next
PWM pulse exceeds 200 microseconds (less than or equal to 5 kHz), 's on-board tickle generator sends
a tickle pulse to maintain plasma ionization in the tube. Because the on-board tickle generator cannot
anticipate when the next PWM Command pulse will arrive, the tickle pulse (which typically lasts for 2–6
μs depending on the laser) can effectively merge with a PWM signal that follows closely afterwards.
When the PWM pulse that follows is short, causing the tickle pulse to become a significant fraction of the
PWM pulse duration, then the tickle pulse effectively substantially increases the length of the PWM pulse
Warning: Serious Personal Injury
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