C A L I B R A T I O N A N D T R O U B L E S H O O T I N G
Calibration Overview
126
LDC-3700 Series
C H A P T E R
5
manner using Ohm’s Law.
I = E / R
where E is the accurately measured voltage across the resistor, and R is the accurately
measured load resistance. I is the actual Laser current in Amps.
3
The LASER output must be on in order to enter the LASER I calibration mode. Enter the
"LAS:OUTPUT ON" command to turn the LASER output on.
4
d.Enter the LASER I calibration mode by issuing the "LAS:CAL:LDI" command. The TEC
display will blank and the LASER display will indicate a current in mA.
5
Input the first actual (measured) LASER output current (as an <nrf value>) via the
"LAS:LDI <nrf value>" command.
If this value is to be measured and entered remotely via a GPIB controlled DMM, for
example, the measured value of the current should not be entered until the LDC−3700B
Series Laser Diode Controller is ready to receive it: The Controller will be ready to
receive the new measured value when, after a "LAS:CAL:LDI?" query is sent, the
response from the Controller is "1".
6
Once the newly measured I value is entered via the "LAS:LDI" command, the Controller
will apply a new current equal to about 25% of the previous set current.
7
Input the second actual (measured) LASER output current (as an <nrf value>) as in Step
5.
8
Once the second actual I value is entered via the "LAS:LDI" command, the new
calibration constants will be calculated and stored into non−volatile memory. In low
bandwidth calibration mode, the LDC−3700B Series Laser Diode Controller will also
perform current limit calibrations for I and P modes as indicated by the
CURRENT LIMIT
LED flashing. The "OPC?" query may be used (after the "LAS:LDI" value is sent) to
determine when the calibration is completed.
9
Change the Laser Mode to I
HBW
(high bandwidth constant current mode) with the
LAS:IHBW command. Repeat the calibration procedure as described above.
I
PD
Current Calibration
The following procedure is for calibrating the LASER I
PD
constant current source. This procedure
calibrates the feedback circuits for constant I
PD
and constant P
PD
modes. When these values are
reached and are stable, the user enters the actual value of the current, as measured by an external
DMM. The LDC−3700B Series Laser Diode Controller then automatically calibrates the LASER
feedback circuits.
Configure the Controller in the following manner for the Laser Controller calibration:
1
With the LASER output off, connect a calibrated ammeter to the PD Anode output of the
Laser Controller output connector (9 pin on rear panel), and connect the circuit of Figure
5.1 on page 114 to the LASER and PD outputs with the correct load resistor for the
FUNCTION
STATE
GPIB COMMAND
LASER MODE
P (constant power)
LAS:MODE:MDP
CAL PD
set equal to zero
LAS:CALMD
LASER LIMIT
90% of FS (full scale of range)
LAS:LIM:Ix
I
PD
Set POINT
4000
µ
A
LAS:MDI
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