User's Guide ______________________________________________________________________
44 __________________________________________________________________ M210667EN-C
Based on the information the auto-calibration feature delivers, the
alignment quality control algorithm evaluates the signal loss due to
reduced alignment quality whenever an auto-calibration situation occurs.
To a certain degree, the signal loss due to reduced alignment quality is
compensated for by the auto-calibration mechanism. The status of the
alignment quality evaluation is given in the frame of the LT31 serial data
message and a realignment request is generated in case the alignment
quality loss is too high. For more information, see section Message
Formats on page 161.
Preventing Contamination
In general, precipitation increases the window contamination when the
precipitation particles reach the transmissometer windows.
The long and narrow weather protection hoods of LT31 reduce window
contamination. However, it is possible that wind-driven precipitation
particles reach the windows and cause increased contamination.
Therefore, a powerful blower is used in combination with a specially
shaped air duct (mounted on top of the measurement unit) to create an air
curtain in front of the windows. This principle is described in Figure 10
below.
0810-075
Figure 10 Window Contamination Prevention Principle
The following numbers refer to Figure 10 above.
1 =
Air stream
2 = Precipitation particle
As the air stream is directed downwards, wind-driven particles are forced
to change their direction.
Measuring Window Contamination
LT31 provides a unique window contamination measurement for the
windows of the transmitter and receiver measurement units.
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