Novanta 32-1 Laser, User Manual

Page: 29 / 58

PLASMA SECTION PAGE | 29
Electrical description
Control of laser operation and power output levels is essentially performed using a single PCB. The Control
PCB connects the modulated signal to the RF amplifier. It also provides electronics to monitor performance
of RF control, output circuitry, input power, temperature, PWM accuracy, provides outputs to an externally
accessible connector, and incorporates reverse polarity protection.
Model 32-1 lasers use a single RF electrode requiring a single modulated RF drive input from the Control
PCB.
The modulated input PWM signal is generated externally to the laser and connected to the input
connector. This signal is connected to an opto-isolator, the output of which is applied to the PWM switch
control circuit. The PWM switch control circuit gates the PWM switch off and on at the frequency and duty
cycle controlled by the modulation source. When the PWM switch closes, a potential of +30 VDC is applied
to the RF Driver. The PWM control circuit provides on/off gating of the PWM switch unless disabled by
the five-second delay, or the fault shutdown circuits.
The five-second delay disables PWM output to the RF amplifier for a period of approximately five seconds
after the Remote Keyswitch link is closed (power ON). Note that the supplied DB-9 jumper plug can be
removed to allow the user to insert a remotely located relay or switch in series with the Remote Keyswitch.
Over temperature fault shutdown occurs when laser tube temperature reaches 60 °C ±2 °C.
Control board operation begins when the supply voltage rises above +18 VDC and remains below +36
VDC. After start-up, the control board will shut the laser down if supply voltage falls below +15 VDC or
rises above +36 VDC.
If an electronics failure causes the control board to output PWM power to the RF Drivers more than 20%
of the PWM input, a fault shutdown will occur.
To reset after any fault shutdown, correct the problem(s) then cycle the power on/off to the laser for 30-
seconds. During any fault shutdown, the fault shutdown output (Pin 1 of the DB-9 connector) will latch to
low state until a reset occurs.
Power-On Reset is defeated on all OEM versions. OEM customers must provide this required safety feature
elsewhere as part of their equipment integration.
Cooling
32-1 electronics are mounted opposite the laser tube in the smaller section of the “H” bay and share the
same cooling removal as the plasma tube. Typical efficiency of CO2 laser plasma tubes operating in a
TEM00 mode is 10% to 12% (radiation out to RF power in). Factor in the conversion efficiency of AC input
to RF output and the overall “wall plug” efficiency of these lasers drops to about 6% to 8%resulting in a
considerable amount of heat removal, even at 5 W output power levels; therefore, external cooling in the
form of forced air is required.