User's Guide ________________________________________________________
32 _____________________________________________________ M210283en-A
The window contamination measurement circuitry uses a
separate IR LED and a detector located on the opposite
sides of the window edges to measure window
contamination with the same principle as FS11. The change
of the contamination signal from the clean value is
proportional to the contamination on the window. The
window contamination value of the status message indicates
the reduction in transmittance of the window. For example,
a contamination value of 10 % means that the window
transmittance has decreased 10 % and it is now only 90 %
of the original value.
Contamination Compensation
The window contamination value is used to calculate the
required compensation for the background luminance
values. The contamination compensation is only performed
with moderate contamination when reliable background
luminance measurements can still be made. If the
contamination compensation is disabled with the FS11
command SET CONTAMINATION_COMPENSATION
BL_SENSOR OFF (or SET
CONTAMINATION_COMPENSATION OFF when
given directly to LM21 via a maintenance terminal), no
contamination compensation is made.
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