Mira Visibility Sensor 3544/3544 EX (forward scattering)0 pages

Mira Visibility Sensor 3544/3544 EX (forward scattering)

Visibility in the atmosphere is of great interest for road
and sea traffic and in aviation. The MIRA Visibility Sensor
3544 is designed to fulfill the demand for a small, low
power unit to be operated with Aanderaa Measuring
Stations. Visibility is often limited by fog and haze and
the sensor is de­ ign­ d to detect these factors.
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The sensor consists of an aluminum body containing all
necessary solid state electronics and two vertical legs. It
is furnished with a standard Aanderaa meteorological
sensor foot. It is a rugged, watertight, corrosion free
and solid state sensor with minimum maintenance
requirements. In one leg of the body, an infrared (IR)
light emitting diode is installed at an angle of 25 degrees.
The opposite leg contains an IR photo detector. The
diode and the photo-detector are protected against
clogging by a cover.
The sensor has two operating modes, Normal and
Fast sampling Modes, which can be selected by the
Mode Switch. In Normal Mode, used when the sensor
is solar-cell or battery powered, the sensor transmits
an infrared light beam every minute. If fog or haze
are present, forward scattered light from the particles

will be detected by the photocell thus giving a signal
with good correlation to the visibility in the ambient
air. The photo current which is proportional to the
scattered light, is amplified, averaged, converted to
visibility and stored in the sensor as a 10 bit digital
signal ready to be read by the Sensor Scanning Unit
or data logger.
If the sensor is powered from Mains, fast sampling
mode can be used to increase the number of samples
taken in a measurement cycle. This will improve the
accuracy of the sensor. In this mode the light beam is
transmitted every 6 seconds.
To avoid false scattering from surrounding objects,
the sensor must have free horizontal distance of at
least 15 cm and a free vertical distance of more than 1
meter. This is taken into consideration when installing
the sensor on the sensor arm of a Road Weather Station
4030 or Automatic Weather Station 2700.
For direct connection to a Programmable Logic Controller
PLC, a Signal Converter, part no. 3429, is available for
converting the data to 0-5VDC and 4-20mA signals.

D294 - Jan 2013