6300 Series ComboSource User’s Manual · Page 35
However, remote voltage sense does have a few drawbacks:
1. If the remote sense wires are disconnected, it disables the hardware
voltage limit as well as the measurement of laser voltage.
2. Requires two additional wires to be run to the device.
It is the first of these two drawbacks that is of the biggest concern. In order to
protect against this fault, the instrument always monitors the local voltage at the
connector as well as the remote voltage, and if the difference is too great, a
warning message is displayed. Once the warning is displayed, it will not be
displayed again until the output is turned off and back on. The warning can be
disabled in the menu by setting the Vf Sense Warn to No.
Using remote voltage sense is very simple. First connect pin 4 of the Laser
Output DB-9 to the laser cathode, and pin 8 to the laser anode, then in the
menu, set Vf Sense to Remote. Indicated voltage will now be the remote diode
voltage.
When using remote voltage sense, any Cable R setting is ignored.
Using the ‘Cable R’ Setting
The Cable R setting allows you to calculate the voltage at the laser by
subtracting the voltage loss through the cable and connectors. This is done by
measuring or calculating the cable resistance and entering the value, in ohms,
into the menu. The instrument will then use the V = I * R formula to calculate the
voltage loss in the cable and subtract that from the actual measured voltage,
displaying the result as Vf on the display.
Common values for Cable R range from 0.0300 Ω to 0.0900 Ω, but can be
significantly higher if you have long runs, many connector interfaces, or small
gauge wire.
While it is possible to use a DMM to measure the resistance of the cable,
because resistance is so small, you will not typically get proper readings (most
DMMs are not designed to properly measure small resistances). A better
approach is to use the instrument to drive current through the system and then
measure the voltage loss to determine resistance. There are two ways to best
calculate the voltage loss:
Measure the Voltage at the Laser
If you have an accurate DMM and can measure the voltage across the laser (or
accurately know the voltage of the laser at a specific current) and voltage across
the pins at the Laser Output connector, then the difference between the
To Next Page
Loading...