Page 26 · 685 Series
ComboPak
User’s Manua
l
3.
The hardware safety circuits use the remote voltage, providing for a
greater degree of protection (
Vf Limit
works on the remote voltage at
the laser rather than the local voltage at the connector)
4.
Works in voltage control mode
The diagram below shows conceptually how to wire the laser to the
ComboPak
,
using a 4-wire connection:
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 generated. Once the warning is generated, it will not be
generated again until the output is turned off and back on.
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
(LASER:VSENSE 1). 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 setting the value, in ohms,
using the LASER:CABLER command. 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, returning the result as Vf.
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.
685
LDA Voltage Sense
LDA
LDA
LDA Voltage Sense
