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
Remote Calibration
02_03
LDC-3926339
73
C H A P T E R
5
Remote Calibration
The LDC-3926339 Modules can be calibrated remotely via the GPIB Interface. All
of the required calibration commands are listed in Table 4.1 on page
37
. The
remote calibration procedures are general guidelines for writing a program to
calibrate the module.
There are three calibration adjustments for the current sourcemodule: calibration
of the constant current (LDI) source, calibration of the constant light power (I
PD
)
feedback circuit, and calibration of the laser forward voltage (LDV) measurement.
LDI Calibration
This procedure is for remotely calibrating the laser current source. The internal
calibration procedure sets the current to two values; you must enter the exact
laser diode current measured at both of these points.
1
With the output off, connect a 1
Ω
, 50 W resistor across the laser output terminals (Laser
Anode, pin A3, and Laser Cathode, pin A2).
2
Connect a calibrated DMM across the load resistor and calculate laser current (LDI) in the
following 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 (a 4-point probe resistance measurement is recommended). I
is the calculated current in Amps.
Note:
ILX recommends the load resistor be temperature-controlled during the calibration.
Alternatively, the current can be measured directly using an ammeter with a range of at
least 6 A, and accurate to ± 0.001 mA. If you use the ammeter, you must connect the
ammeter in series with a load resistor with a nominal value of 1
Ω
. Note that auto-ranging
ammeters may cause calibration errors.
3
Send the command
LASER:CAL:LDI
to begin the LDI calibration.
The internal calibration procedure begins by setting the laser output current to
approximately 10% of its full range. Allow the current to settle for at least 10 seconds.
Note:
If the calibration value is measured and entered remotely via a GPIB controlled
DMM, the actual value of the current cannot be entered until the calibration procedure is
ready to receive it.
4
Send the query
LASER:CAL:STATUS?
to make sure the internal calibration procedure is
ready for a measurement.
The calibration procedure is ready for a measurement if it returns the value 1. Query the
status until the value that is returned is 1.
5
Enter the measured current in Amps by sending the command
LASER:CAL:MEAS
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