O P E R A T I O N S
Operating from the Front Panel
20
LDC-3926339
C H A P T E R
2
Setting Constant Photodiode Current Mode (Ipd)
If the correct photodiode responsivity (CalPD) value is not known, the module can
still drive the laser at a constant light power. The Constant Photodiode Current
(Ipd) mode controls the laser drive current so the monitor photodiode current
remains at a constant set point.
1
Press the LAS soft key to enter page 1 of the laser channel setup menu.
2
Set the current source mode to Photodiode Current mode (
Ipd
).
2a
Press
NEXT
until the Mode field is highlighted.
2b
Select
Ipd
using the INC/DEC keys or the Adjust knob.
Note:
Repeatedly pressing the INC/DEC keys or turning the Adjust Knob cycles through
the Constant Current low bandwidth (
Ilbw
), Constant Optical Power (
P
), Constant Current
high bandwidth (
Ihbw
), and Photodiode Current (
Ipd
) control modes.
3
Set the voltage limit (Vlim) and current limit (Ilim).
3a
Press
PREV
to select the voltage limit (
Vlim
) parameter.
3b
Using the Adjust Knob or the numeric keypad, set the Vlim value and press
Enter
.
Set the voltage limit slightly above the operating voltage of the laser diode to provide
maximum protection. The voltage limit protects your laser by shutting off the source driver
if the laser voltage exceeds the Vlim value.
3c
Press
PREV
to select the current limit (
Ilim
) parameter.
3d
Using the Adjust Knob or the numeric keypad, set the Ilim value and press
Enter
.
The current limit protects the laser by never allowing the drive current to exceed the Ilim
value, independent of the current set point and the controller mode (Constant Current or
Constant Power).
Figure 2.11
Laser Page 1
4
Press
F4
continue to LAS page 2.
5
Press the PREV/NEXT softkeys to highlight the photodiode current setpoint (
Ipdset
)
field.
6
Using the INC/DEC keys, Adjust knob, or keypad, enter the photodiode current setpoint
value.
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