THORLABS ITC502, Operation Manual

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2.23 Laser voltage measurement
ITC500 / page 54
2.22.1.4 Cable damage monitoring
If the interlock line is installed in parallel to the line for the laser current, a cable
damage monitoring may be realized as well.
An interruption of this line will open the interlock.
2.22.1.5 Laser ON/OFF-Display
The interlock can also be closed by switching a LED with the anode to pin 1 and the
cathode to pin 5 of the 9pin D-SUB jack in parallel with a 500
Ω
resistor. The current
is about 7 mA, this will make any commercially available LED light up.
This LED (only one LED is allowed) may be looped in at any point into the interlock
line and may thus serve as an independent ON/OFF display.
2.23 Laser voltage measurement
The ITC5xx constantly measures the laser voltage at the output jacks of the unit. For
a precise measurement connect pin 6 directly to the LD-cathode and pin 9 directly to
the LD-anode (respectively pin 11 and pin 14) to avoid measuring the voltage drop of
the wiring (4 pole measurement).
We recommend to use “twisted pair“ wiring for the monitor diode current, bias voltage
and laser voltage measurement respectively in a common shield. The shield has to
be connected to ground (pin 3).
(Refer to chapter 1.9.1, “Pin assignment for the laser diode output“ on page 20)