User`s manual

4200-DR Series LaserSource User’s Manual · Page 23

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

measurements are not required, and the error can be ignored. However, if

accurate voltage measurements are required, the 4200-DR 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 4200-DR 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 4200-DR,

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.

4200-

LDA Voltage Sense

LDA

LDA Voltage Sense