Lightwave Communications LDX-3232 - Manual (Page 109)

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
Local Calibration of the LDX-3232 Current Source
04_06 LDX-3232 93
C H A P T E R
6
LDX-3232 Series Current Source then automatically calibrates the LASER
feedback circuits.
Configure the Current Source in the following manner for the Laser Current
Source calibration:
a. With the LASER output off, connect a calibrated ammeter to the PD Anode output of
the Laser Current Source output connector (9 pin on rear panel), and connect the
circuit of Figure 6.1 to the LASER and PD outputs with the correct load resistor for
the Current Source model you are calibrating (See Table 6.2).
Note: If a precision ammeter is not available, use a zero-Ohm jumper in place of the
ammeter. Then, place a calibrated DMM (with 0.1 mV resolution) to measure the voltage
across the resistor, R1, as shown in Figure 6.1. Calculate the current in the following steps
by using Ohm's Law:
I = V/ R
--where V is the accurately measured voltage across the resistor, and R is the accurately
measured load resistance. I is the actual photodiode current to be measured by the
LDX-3232 Current Source. (A 4-wire [Kelvin] resistance measurement is recommended.)
b. Press the (MODE) ON switch to turn the current source output on. Verify proper
operation, i.e. the I
PD
measurement (via DMM) and setpoint should be close, and the
unit should not be in current limit.
c. Press the (GPIB) LOCAL and FINE switches at the same time to place the Current
Source in its I
PD
Current Calibration mode.
After a few seconds the display will show the I
PD
setpoint value.
d. After the value on the display is stable (has not changed by more than one digit for
several seconds) the LDX-3232 Current Source is ready for the actual I
PD
value to be
entered.
Press and hold in the (PARAMETER) SET switch and turn the adjust knob until the
display shows the actual monitor current, as shown on the calibrated ammeter (or the
calculated I
PD
value from Step a).
e. Release the (PARAMETER) SET switch to store the first calibration value. The
Current Source will then set the second calibration current, approximately one-fourth
(1/4) of the original current. (For example, if the first calibration setpoint was 4000 µA,
the second setpoint will be about 1000 µA.)
f. Press and hold in the (PARAMETER) SET switch and turn the adjust knob until the
display indicates the actual current as measured by the ammeter or as calculated.
Function State
MODE P (constant power)
CAL PD set equal to zero
CURRENT LIMIT 90% of FS (full scale of range)
I
PD
SETPOINT 80% of FS