LAMBDA DG-4 PLUS & DG-5 PLUS OPERATION MANUAL – REV. 3.05B (20131009)
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Figure 3-5. DG-4 output attenuation.
3.7.7.3
Attenuation
If the Output Galvanometer value is either slightly increased or decreased from the value
that produces the peak output, the light coupled into the light guide will decrease as
schematically depicted in the figure on the following page. The nominal relationship between
galvanometer value and output is shown in the plot below. The exact relationship may vary
from unit to unit and filter position to filter position. The actual attenuation produced must
be determined by the user. The degree of attenuation produced by increasing the
galvanometer value is similar to that produced by an equivalent decrease. Remember,
though, that you are limited to an overall range of 0 to 4095. If the output galvanometer
value for maximum output is already within 1000 units of a limit (0 or 4095) it is logical to
attenuate by changing the value in the direction that moves away from that limit. This
method is very useful for attenuating output by less than 1 log unit. It is recommended that
you use neutral density filters when attenuation of 1 log unit or more is desired.
Figure 3-6. Log of attenuation vs. change in output galvanometer value.