Newport 500B Series, User Manual, Page: 30 / 64

System Operation 29
Once the fault is corrected, the OUTPUT ON switch must be pushed once to
clear the error indication, and a second time to restore current to the laser
diode.
LIMIT Indicator LED
A soft limit occurs when the output current gradually exceeds a preset value,
clamping the current flow at that level and causing the LIMIT LED to blink
until the threshold is no longer exceeded. A hard limit, indicated by a solid
yellow LED and the ERROR LED will occur if the external input is over
modulated when first attempting to turn on the output. The error must be
cleared before normal operation can occur.
4.1.6 Laser Enable
This key switch is a safety feature that allows an OUTPUT about 4 seconds
after being turned on. The key may only be removed in the OFF position.
4.1.7 Display Section
The display located in the top center of the front panel is a 4 digit green LED
array. It reads current in mA for all Series 500B models. Pushing the switch
repeatedly, cycles through display values as described below. Display modes
can be toggled when the output is either ON or OFF.
SETPOINT Display
This mode allows setting diode current levels with the control knob before
actually turning on the output. If constant current (I) mode is selected, the
current setpoint corresponds to output laser diode current. If constant optical
power (P) mode is selected, the current setpoint corresponds to monitor
photodiode current.
LIMIT SET Display
This mode allows setting diode current limit level with the control knob.
LD CURRENT Display
This readout measures actual current flow in milli-Amps to the laser diode.
The current level will drop to zero when the output is OFF. The display
shows the average output drive current if the laser diode is modulated with a
varying external input waveform.
PD CURRENT Display
Using the monitor photodiode current (Im) displayed, a conversion table
supplied by the diode manufacturer will indicate actual optical power level.