Local Calibration; Current Source Calibration - ILX Lightwave LDC-3926339 User Manual

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
5
C H A P T E R

Local Calibration

Local Calibration
There are three calibration adjustments for the current source module: calibration
of the constant current (LDI) source, calibration of the constant light power (I
feedback circuit, and calibration of the laser forward voltage (LDV) measurement.

Current Source Calibration

This procedure is for calibrating the laser current sources. The internal calibration
procedure sets the current to two values; you must enter the exact laser diode
current measured at both of these points.
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Note: ILX recommends that the load resistor be temperature-controlled during the
calibration. Alternatively, the current may 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 approach,
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.
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LDC-3926339
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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).
Current flows from the anode to the cathode.
Connect a calibrated DMM across the load resistor.
Calculate laser current (LDI) 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.
Press MAIN to enter the LDI calibration mode.
Press the Sys. Config softkey, then the Cal. softkey.
Press the Cal LAS softkey.
Press the LDI Cal softkey. The LDI calibration screen appears.
Press Start. The internal calibration procedure turns on the output and drives the LD
current to approximately 10% of full range. Allow the current to settle for at least 10
seconds.
Calculate or measure the actual current through the load resistor and enter the value (in
mA) into the IReal adjust field and press ENTER.
Do not enter more than eight characters, including the decimal point. The internal
calibration procedure sets the LD current to approximately 90% of full range. Allow the
current to settle for at least 10 seconds.
Measure the actual current and enter the value into the IREAL adjust field.
After you have entered the second value, the internal calibrations procedure calibrates the
LD current measurement circuit, the LD current source for both low and high bandwidths,
and the LD current limit circuit.
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PD