4.2 Controlling the PM100A
16
After performing a zero adjustment, the detected zero value will be included in all
power readings. The detected zero value may influence the wavelength corrected
calculated full scale power range values in the lower power ranges.
Photodiode sensors emit small current levels, even when no photons hit the active
area – the so called dark current, that is temperature dependent and in the region of
some nA for silicon and InGaAs sensors and up to some µA for germanium sensors.
Thermopile sensors need to be zeroed when thermal differences between active
area (thermal disk) and the sensor heat sink appear when no light hits the active
area or when the heat sink gets hot under light exposure. The zero value will be
negative when the heat sink is hotter than the active area and positive, when the
active area is hotter than the heat sink. When both heat sink and active area are at
room temperature a zero voltage of some µV is normal.
4.2.3.4 Setting an Attenuation / Gain Factor
To set an attenuation or gain factor that will be taken into account when calculating
the displayed power, enter the system menu and navigate to the Attenuation item.
MENU \ Attenuation
When confirming this item with the OK key an attenuation or gain factor from 60 dB
to -60 dB can be entered by the keys. A positive value will set an
attenuation factor. Confirm the setting with OK and quit the menu by or .
The attenuation set value in dB will be indicated in the status display above the
measurement value.
This feature can be used to display the origin laser or probe power, with having a
filter or beam splitter in the system; or to enlarge the measurement range of a power
or energy sensor with a calibrated filter.
Attenuation set value
Figure 8 Attenuation
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