Arroyo Instruments LaserSource 4400 Series, Руководство пользователя

Страница: 35 / 64

4400 Series LaserSource User’s Manual · Page 35
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. 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
Output connector, then the difference between the measured
voltages is the voltage loss in the cable. Use this formula to calculate resistance:
𝐶𝑎𝑏𝑙𝑒𝑅
𝑉 𝑉
𝐼
V is in volts, I is in Amps.
Short the Connection at the End of the Cable
A second method, which can be done with just the 4400, is to short the cable at
the end of the cable (nearest the laser diode), drive current through the cable
and measure the voltage. The resistance is found using a simpler version of the
formula above:
𝐶𝑎𝑏𝑙𝑒𝑅
𝑉
𝐼
Note that the current is expressed in
amps , not milliamps . The easiest way is to
drive 1 Amp of current. When I equals 1 Amp, the displayed voltage is the
resistance of the cable. Another method is to drive 10 Amps of current and then
divide the voltage by 10.
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 4400 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 below). This means that the Vf