Chapter 3 ______________________________________________________ Functional Description
VAISALA _______________________________________________________________________ 45
A separate window transmitter module emits a light beam which crosses
the V-shaped windows of the instrument. Using a specially shaped part
of the measurement unit enclosure as a reflecting surface, the light beam
is directed to the corresponding window receiver optics and electronics
which are part of the measurement CPU board. This principle is
described in Figure 11 below.
LT31 uses the measurement CPU board’s measurement for the
following:
- Measuring the real transparency of the windows.
- Compensating for window contamination in the short term.
- Detecting possible blocking situations.
- Creating related warning/error messages.
0401-028
Figure 11
Window Contamination Measurement Principle
The following numbers refer to Figure 11 above.
1 = Reflecting
surface
2 = Windows
3 = Window
transmitter
4 = Window
receiver
5 = Main
board
Hardware Descriptions
The Vaisala Transmissometer LT31 system contains the following
functional units: