M A I N T E N A N C E
Calibration Adjustments
03_03
LDT-5525
27
C H A P T E R
3
Monitor Current (Power Mode) Calibration
The following procedure is for calibrating the I
PD
measurement and power set
point. This procedure calibrates the feedback circuits for constant power mode.
When the calibration set point values are reached and are stable, the user enters
the actual value of the current, as measured by an external DMM.
•
With the LASER output off, connect a calibrated ammeter to the PD Anode output of the
LDX-3500 Series Precision Current Source, and connect the circuit of Figure 3.1 to the laser
and PD outputs (R3 = 5
Ω
, LDX-3565; 5
Ω
, LDX-3545; or 10
Ω
, LDX-3525).
If a calibrated ammeter (with 0.1 mA resolution) 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 3.1.
Figure 3.1
IPD Calibration Circuit
Calculate the current in the following steps by 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.)
•
Set the LDX-3500 Series Laser Diode Current Source’s mode to P. Set the current range to
the lower output range. Set the current limit (I LIMIT) to 80% of full scale. Set the P LIMIT to
100% of full scale (Power limit may be ignored during calibration). Set the power set point to
4.000 mW
(
LDX- 3525) or 8.000 mW (LDX-3545) or 40.00 mW (LDX-3565), and set the CAL
PD parameter to 1.000 (mA/mW).
This puts the LDX-3500 Series Precision Current Source into a mode in which the measured
monitor current is equivalent to the power.
•
Press the ON switch to turn the output on. Verify proper operation, i.e., the power set point
should be close, and the unit should not be in current limit.
•
Press the OUTPUT ON and ADJUST ENBL switches at the same time (for one second) to
place the LDX-3500 Series Precision Current Source in its calibration mode.
The display will blank for two seconds. Then the output will come on (if it wasn’t already) and
the display will show the power set point value.
U1 T IL117
1
2
3
4
5
6
A
V
R 3
R 2
100
9-Pin D -Sub
LD C athode (5)
LD A node (9)
PD C (6)
P D Anode - (7)
Voltm eter
Am m eter
R 1
49
Ipd Current
R4
1 M
C ALIB R A T IO N C IR C U IT
9 V Batt
Interlock - (1)
Interlock - (2)
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