CALIBRATION AND TROUBLESHOOTING
Calibration Overview
118 LDC-3700 Series
CHAPTER 5
ITE Current Calibration
This procedure is for calibrating the ITE bi−polar constant current source. This procedure calibrates
the zero current set point automatically, then it automatically drives the TE current output to
internally set limits of ±2 amp. When each of these values is reached and is 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 TEC current source and limits.
1 With the output off, connect a 1 Ω, 20 W resistor across the TEC output terminals (TE
Module + and TE Module −).
2 Connect a calibrated DMM across the load resistor. You will be calculating TE 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 calculated current in Amps. (A 4−point probe
resistance measurement is recommended.)
3 Make sure that the TEC output is off before entering the I
TE
calibration mode. Press the
(GPIB) LOCAL and (TEC DISPLAY) I
TE
switches at the same time to place the Controller
in TEC Current Calibration mode.
The Laser display blanks and the TEC display drives the output to a value of zero (0.000)
amps as the Temperature Controller calibrates itself. After 20 seconds, the TEC controller
drives the output to 2.000 amps. Once stable, the temperature controller is ready to enter
the actual TE current value.
4 Press and hold the (PARAMETER) SET switch and turn the Adjust Knob until the TEC
display shows the correct value (absolute value of the I
TE
measurement). Release the
(PARAMETER) SET switch to store the new calibration value into non−volatile memory
The Controller drives the TE output current to the negative value of −2.000 Amps.
5 Repeat step 4 for the negative polarity of the TEC output current.
After the negative polarity value of the TEC output is entered, the controller automatically
calibrates its current limits and set points, indicated by the flashing TE Current Limit
indicator. The controller then returns to the state before calibration.
Local Calibration of the Laser Current Source
There are three calibration adjustments required for the LASER current source of the LDC−3700B
Series Laser Diode Controller. They are: calibration of the constant current source for both
bandwidths and ranges, calibration of the laser voltage measurement, and calibration of the
constant light power (I
PD
) feedback circuits.
The LDC−3700B Series Laser Diode Controller implements a two−point calibration for the Laser
current source. Two currents (approximately 80% and 20% of FS) are applied to a test load, and the
resulting actual currents are fed back (by the user) to the Controller. The Laser Controller calibration
program uses the two sets of data to calculate new calibration constants. These calibration
constants are used to set the actual current output of the current source.
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