Vaisala FD12P - Manual (Page 31)

Chapter 3 ________________________________________________________________ Installation
VAISALA ________________________________________________________________________ 31
The receiver and transmitter optics should not point towards
powerful light sources or, in bright daylight, reflective surfaces
such as snow or sand. The receiver should point north in the
Northern Hemisphere and south in the Southern Hemisphere.
The receiver circuit may become saturated in bright light, and
the built-in diagnostics will indicate a warning. Intense light can
generate false contamination alarms from the transmitter unit.
Bright daylight will also increase the noise level in the receiver.
The transmitter and receiver should face away from any obvious
source of contamination such as spray from passing vehicles.
Dirty lenses will cause the sensor to report too high visibility
values. Excessive contamination is automatically detected by the
sensor.
Harmful reflections are typically avoided if the transmitter beam
is directed towards a surface, which will reflect most of the light
away from the sensor. The distance of 6 meters shown in Figure
4 below is only for guidance; it is not an absolute requirement.
There should be no flashing lights near the sensor. A flashing
light can cause errors in detecting precipitation towards
No obstacles or reflecting surfaces
0110-178
Figure 4 Recommended Location for the FD12P
The following numbers refer to Figure 4 above.
1 = Transmitter
2 = Receiver