Chapter 7 Calibration 77
where V is the measured voltage across the resistor, and R is the
measured load resistance.
b. Go to the single module display by first pressing the
MENU
button,
then the
Modules
soft key, then the slot soft key that corresponds to the
module to be calibrated.
c. Press the
Setup
soft key, change the
Mode
to
Im
(Photodiode constant
current mode), and set the laser current limit (
Io Lim
) to maximum.
Press the
soft key to return to the single display.
d. Press the
LDD ON
key to turn the laser output on. If a laser on delay
has been set, wait that amount of time to allow the laser output to
engage.
e. Go to the calibration display by first pressing the
MENU
button, then
the
Config
soft key, then the
Cal
soft key, then the channel to be
calibrated. At the calibration screen, press the
Im
soft key. Follow the
on-screen instructions to complete the calibration. The calibration can
be terminated without affecting the stored constants if the
Term
soft
key is pressed at any point prior to completing the calibration..
7.2.6 Remote Operation I
PD
Current Calibration
a. With the laser output off, connect a calibrated ammeter to the
photodiode anode output of the module and connect the circuit of
Figure 34 to the laser and photodiode outputs.
If a calibrated ammeter (with 0.1 µA resolution) is not available, place a
calibrated DMM (with 0.1 mV resolution) to measure the voltage
across the resistor, R3, as shown in Figure 34. Calculate the current in
the following steps by using Ohm's Law:
I = V / R
where V is the measured voltage across the resistor, and R is the
measured load resistance.
b. Select the channel via the
LAS:CHAN
command. Set the laser current
limit to full scale via the
LAS:LIM:LDI
command. Set the photodiode
current set point to ½ full scale via the
LAS:MDI
command. Place the
unit into constant photodiode current mode via the
LAS:MODE:MDI
command.
c. Enter the
LAS:OUTPUT ON
command to turn the laser output on.
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