CALIBRATION AND TROUBLESHOOTING
Calibration Overview
7/01 LDC-3700 Series 119
CHAPTER 5
Current Source Calibration
The following procedure is for calibrating each range of the current source. Start with the low range.
After calibration is complete in this range, switch to the high range and repeat the procedure.
Configure the Laser Controller in the following state:
1 Measure and record the resistance of a 1 Ω, 20 W resistor (a 4−point probe resistance
measurement is recommended). Connect the load resistor across the LASER output
terminals (Laser Anode and Laser Cathode) on the 9 pin connector of the rear panel.
2 Connect the calibrated DMM across the load resistor. Configure the multimeter to
measure voltage in volts. You will be calculating the actual Laser current 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. I is the actual Laser current in Amps.
Note: Check the current measuring range of your multimeter. You may be able to
measure Laser Output current in mA by connecting the meter directly to the outputs of the
Laser Current Source.
3 Press the (LASER MODE) ON switch to turn the LASER output on. The LASER output
must be on in order to enter the LASER I calibration mode.
4 Enter the LASER I calibration mode by pushing the (GPIB) LOCAL and (LASER
DISPLAY) I switches at the same time. The TEC display will blank and the controller will
drive the LASER current output to the set point and the LASER display will indicate output
current in mA.
5 Calculate the actual current through the load as described in step b. Press and hold in the
(PARAMETER) SET switch and turn the ADJUST knob until the LASER display indicates
the calculated actual current.
6 Release the (PARAMETER) SET switch. After the (PARAMETER) SET switch is
released, the Controller will drive the LASER current output to about 25% of the first
calibration set point.
7 Calculate the measured current again through the load resistor.
8 Press and hold in the (PARAMETER) SET switch and turn the ADJUST knob until the
LASER display indicates the actual current as calculated in step 7.
9 Release the (PARAMETER) SET switch to accept the second calibration point. After the
(PARAMETER) SET switch is released, the Controller will calculate the calibration
constants, store them to nonvolatile memory. In low bandwidth calibration mode, the
LDC−3700B Series Laser Diode Controller will also perform current limit calibrations for
I(Constant Current) and P(Constant Power) modes, indicated by the CURRENT LIMIT
Function State
Laser Mode I (constant current low bandwidth)
Range low (lowest per instrument model)
Limit 90% of FS (full scale of range)
Set Point 80% of FS (90% for LDC−3744B)
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