User`s manual

4200-DR Series LaserSource User’s Manual · Page 25

Short the Connection at the End of the Cable

A second method, which does not require a DMM and can be done with just the

4200-DR, is to short the anode and cathode wires at the end of the cable

(nearest the laser diode), drive current through the cable and note the indicated

voltage on the 4200-DR. The resistance is found using a simpler version of the

formula above:

AMPS

RCable 

Note that the current is expressed in amps, not milliamps. The easiest way is to

drive 1A of current. When I

AMPS

equals 1A (1000mA), the displayed voltage is

also the resistance of the cable.

To short the cable, disconnect the laser and short the anode and cathode

together as close to the end of the cable as possible. Ideally, the short should be

done by soldering the anode and cathode wires together to minimize the

resistance in the short itself.

How the Calculation Is Used

The 4200-DR continuously takes the measured current, multiplies it by the

resistance (Cable R), subtracts the result from the actual voltage at the output

connector, and displays this value on screen as Vf. However, there are some

limitations to how the cable loss calculation is used:

1. The value for Vf Limit is always the voltage at the connector (except

when using remote voltage sense, see above). This means that the Vf

Limit must take into account all the voltage required, including the

cable loss (i.e., the voltage displayed if the Cable R value were zero).

2. Cable R is ignored in Vf mode. This means that the set point and

measured voltage are always the voltages at the connector, and Cable

R is not used.