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 The
power supply provides all of the excitation energy and electronic circuitry
necessary to operate, monitor and control the laser. The Lexel power supply
was designed to provide maximum reliability. freedom from component failure
and troublesome maintenance. One major design objective was to eliminate
power transistor failures that notoriously plague other power supply
designs.
We have selected conservatively-rated components, provided substantial heat removal
improvements, and introduced innovative control, protective and safety
systems. Water hoses were eliminated from inside the power supply. All
components were placed for easy access and marked for clear identification.
Advanced new circuits were provided for power stabilization. The resulting
approach has proven to be completely successful.
The Lexel ion laser
power supply is the most reliable yet developed, providing a
degree of convenience, flexibility and safety unmatched in the industry.
 The layout
of controls, indicators and meters on the front panel gives maximum
operating convenience and control plus clear indication of the performance
of the laser. The major design features associated with the power supply
control panel are shown in the photo above, and are described below. (To view a close-up
picture of the exterior of a Lexel power supply, click on the photo above.
To view details of the inside of the power supply, click on the photo at
right.)
Push-button operation
We exclusively
use push-button main power control on all our power supplies.
It is
quick, positive and the safest type of power control for ion lasers. Push
the POWER ON button and the laser is energized. After an automatic 20-second
delay for the plasma tube cathode to warm up, push the LASER START button to
ionize the plasma tube, and the laser is in full operation. At any time a
push of the POWER OFF button will de-energize the laser.
The push
buttons operate the main line contactor in conjunction with the interlock
circuit. The momentary opening of any interlock or protective circuit in the
interlock chain will immediately open the line contactor de-energizing the
laser just as positively as pushing the POWER OFF button. The laser cannot
"accidentally" restart on its own. The interlock must re-close and the POWER
ON button must be pushed to turn the laser on again. The laser operator has
complete and positive control of the laser's operating condition.
The
push-button type control circuit also can permit remote turn on and turn off
of the laser from the user's remote control relays or interlock switches.
Decisive indicator lights
The
meaning of the indicator lights on Lexel lasers is clear and unambiguous.
When an indicator light is ON, the circuit is ON and OK. If the light is OFF
that part of the circuit is OFF or open. Indicator lights are provided to
show the condition of the incoming AC line, each of the main fuses, and the
interlock chain. Indicators also show when the power is on and when the
laser is ready to start.
Interlock indicators
Lexel
lasers are fully interlocked to prevent operation under conditions that
could damage the laser or present an electrical or optical hazard. Only when
all of the interlocks are closed will the INTLK indicator come on and allow
the laser to be energized. Model 95 Series power supplies have additional
indicators which show the condition of each individual interlock in the
interlock chain.
Metered electrical parameters
All Lexel
power supplies have a panel-mounted meter which allows continuous monitoring
of the LASER CURRENT or the transistor REGULATOR VOLTAGE. The operative
condition of the plasma tube and the regulator circuit are instantly
available. The Model 95 series also provides switch positions for measuring
the tube voltage and the AC control voltage.
Laser power controls
The output
power of the laser is set by adjusting the current level through the plasma
tube. This can be done in Current or Light Control mode.
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Current regulation allows direct control of the current through
the plasma tube via an external source.
The current control circuit holds the laser current at the precise level
selected regardless of line voltage fluctuations.
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Light regulation provides the ultimate in laser output
stabilization. A small portion of the light is sampled within the laser
and compared to a reference signal in a differential circuit that
automatically adjust the laser current to maintain a constant output.
The LIGHT CONTROL
knob is a 5-turn precision potentiometer which permits the exact power
level to be set and maintained. This feature also allows for the light level to be
modulated externally with a ± 10 volt signal.
Multirange power meter
The output
power of the laser can be continuously monitored using the panel mounted
power meter. The range of the meter can be switched to accurately measure
power levels from the full capability of the laser to very low levels.
Safety features
Safety is
one of the most important aspects of Lexel's design. Protective features
have been designed into the power supply to prevent accidental exposure to
areas of high voltage. An electrical safety interlock de-energizes the high
voltage if the cover is removed. Areas inside the power supply that are
connected directly to the AC line are covered with additional protective
shielding or labeled with the appropriate warning. Electrical test jacks are
provided so that the major electrical parameters can be safely measured.
Lexel
lasers comply with all applicable laser safety standards as prescribed by
the U.S. FDA Center for Devices and Radiological Health (CDRH) Laser
Products Performance Standards. Two of these CDRH features are shown on the
power supply control panel.
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The KEY CONTROL can be used to
prevent the laser from being operated by unauthorized personnel. If the
key is removed, the laser will immediately turn off. It can not be
re-energized unless the key is replaced and turned to the ON position.
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The LASER RADIATION EMISSION
INDICATOR is illuminated when the power supply is turned on. It provides a
prominent visual signal for at least 20 seconds prior to the start of
laser operation and as long as the laser remains energized.
Magnetic field control
The
magnetic field provided by the electromagnet surrounding the plasma tube has
been computer designed to provide the optimum performance on the major
wavelengths provided by Lexel lasers. Occasionally, laser users have
applications which require changing the magnetic field for the weak 472.7 nm
and 465.8 nm blue lines. The optional Variable Magnetic Field will provide
this control.
Multilevel overload protection
Lexel
lasers are protected from overcurrent or overvoltage damage by four levels
of overload protection. Each level protects against a progressively more
serious condition.
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A
current limit circuit prevents the laser current from exceeding a fixed
safe limit under normal operation. The laser cannot be operated at a level
that would damage any component.
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If a
large line voltage surge or component malfunction were to cause the laser
current to exceed the fixed limit, an overcurrent trip circuit will open
the line contactor and de-energize the laser.
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A more
severe overload will cause the fast-acting diode protective fuses to blow,
removing the AC voltage from the rectifiers.
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The LINE
circuit breaker serves as the final level of overload protection
completely removing all AC voltage from the power supply components in
case of a major short circuit. Lexel lasers respond to overloads by
shutting off, not blowing up.
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