Page 34 · 6300 Series ComboSource User’s Manual
The 1220B or 1221B cables recommended by Arroyo Instruments are shielded
twisted pair, and will provide good modulation performance.
Current (A) Recommend Wire Gauge
1 or less 24 AWG
2 22 AWG
4 20 AWG
Compensating for Voltage Loss
All cables and connectors have a small, but measureable, resistance. When
driving current through them, this resistance causes a voltage loss in the cable,
and if not compensated for, will result in errors in laser or LED voltage
measurement. In many cases, this is not a problem, as highly accurate voltage
measurement ares not required, and the error can be ignored. However, if
accurate voltage measurements are required, the ComboSource offers two
methods to compensate for this loss: the Cable R setting and four-wire sense.
Cable R compensation is software only, so it requires no special wiring to
implement. Four-wire sense, on the other hand, does require additional wiring,
but is the most accurate method. Details on both are found below.
Using Remote Voltage Sense
The ComboSource supports remote (4-wire type) voltage measurement of the
laser diode, providing a higher accuracy voltage measurement by directly
measuring voltage at the diode itself. While the Cable R setting described below
can provide some of the same benefits of remote voltage sense, remote voltage
sense is a superior method, and they differ in a few key ways:
1. No need to calculate cable resistance
2. Voltage measurement is accurate even if the cable resistance changes
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
ComboSource, using a 4-wire connection:
6300
LDA Voltage Sense
LDA
LDA
LDA Voltage Sense
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