Lightwave Communications LDX-3232 manual Constant power, Cal Pd, Set equal to zero, IPD Setpoint

CA LI BRATION AND TR OUBLESHOOTING

Local Calibration of the LDX-3232 Current Source

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:

Function	State
MODE	P (constant power)
CAL PD	set equal to zero
CURRENT LIMIT	90% of FS (full scale of range)
IPD SETPOINT	80% of FS

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 IPD 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 IPD Current Calibration mode.

After a few seconds the display will show the IPD 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 IPD 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 IPD 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.

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