Chapter 3 ________________________________________________________________ Installation
VAISALA ________________________________________________________________________ 57
Background Luminance Options
FS11 can be fitted with one of two Background Luminance Sensor
options:
1.
LM21 Background Luminance Sensor, for use in Runway Visual
Range (RVR) systems
2.
Day/Night Photo Switch, for general nighttime meteorological
visibility
LM21 Background Luminance Sensor
The optional LM21 sensor offers the means for measuring ambient light
level or background luminance in RVR applications. The sensor is
mounted on the Sensor Arm, which is attached to the rear panel of the
radiation shield. The mechanical installation of LM21 and Sensor Arm is
shown in Figure 20 on page 41. Assembly instructions are described in
detail on pages 38 and 39, steps 13, 14, and 15. The sensor should be
directed to face the North sky in the Northern hemisphere. Direct
sunlight into the sensor must also be avoided. The Background
Luminance Sensor is normally tilted at an angle of 20° to 50°. Generally,
an installation angle of 30
°
is recommended when there is no special
reason to use a higher one.
The Background Luminance Sensor is used for measuring the
background against which the pilot views the runway lights or runway
markings. A compromise must be made to achieve a measurement as
representative as possible and, on the other hand, to meet the installation
requirements. The luminance sensor must not face the runway lights
directly.
For detailed information of LM21 Background Luminance Sensor, see
the LM21 User's Guide. For system configuration, refer to section LM21
Background Luminance Sensor on page 91.
Day/Night Photo Switch
In certain applications it is necessary to calculate a special night visibility
value from the measured MOR. In these cases a simple day/night photo
switch is sufficient for discerning between day and night ambient light
conditions. A low voltage (12 DC) model of the photo switch has to be
used. The switch output can be connected to the photo switch input on
the FSC202 processor board. See Figure 32 on page 58 for wiring details.
For system configuration, refer to section Day/Night Sensor on page 91.
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