Manual for MiniBSV

MiniBSV is a low price fog sensor. It will work fine for many applications like multisensor for warning systems.

The sensor is sensitive for fog particles in a zone about 10 to 20 cm ahead of thelocation of the sensor who limit the visibility in the air. These particles are normallythe microscopic water particles constituting fog, but they may also be snowflakes,
raindrops or air pollutants. But the most indications of low visibility are because offog or snow.
The sensor is heated to a few degrees above ambient temperature in order to keep
moisture away. In order to keep the electronics dry a membrane ventilator thatkeeps the pressure inside at the same level as outside. This prevents liquid waterfrom sucking into the sensor through micro cracks etc. at falling temperature – acreative solution to a big problem.
The sensor produces analog and digital signals:

About the analog output:
The microprocessor controls the analog output giving the visibility directly(vis=1000 meters gives 1 Volt, and vis=0500 meters gives 0.5 Volt etc. up to 4 Volt
at 4000 meters by 20mV steps). While temporal measurement errors such as
sensor saturations by sunlight or reflections from an object it the sensitive zone likean insect of fallen snow covering the front, the sensor outputs 5 Volt as an error
code. The analog output is refreshed at each every 30 seconds after once thevoltage is dropped to 0 volt.

About the digital output:
We recommend this digital output since more and better information can be takenfrom it. The calculated data is presented in digital form as an ASCII string on theRS232output, 1200 baud 8N1, that is transmitted “streaming” every 30 seconds thefixed length data. This string can be received by many loggers with RS232 inputs but
also by a PC via the serial port and with a terminal program like TeraTerm.
An example of an output string:
amb=+100 alfa=+0.0012 vis=2500
The first figure – the amb parameter is uncalibrated measure of the ambient solar
irradiance in W/m2. The sensitivity depends strongly on how the sensor is aimed. It
may vary as much as -50 to +100%. But the repeatability is much better and theoffset error between units is only +/- 2. The sensor can, when mounted, be calibrated
by comparing it with an irradiance sensor. But a simple method is to take data from aclear day at noon. If the sun is 60 deg or more above the horizon the irradiance is
not far from 1000 W/m2. The measurement is not very accurate, but it may be usefulfor instance for telling if it is day or night.
The second figure is the so-called extinction coefficient often called alfa. The
relation between the extinction and visibility is alfa=3/VIS.* The alfa parameter canbe used for monitoring trends in visibility when the visibility is larger than 4,000
meters. But note that the absolute accuracy in alfa is limited in such cases.
The third figure – the vis parameter – is the measured visibility in meters.
If the optical receiver is saturated by for instance sunlight or reflections froman object in the sensitive zone like an insect or fallen snow covering the front,
the visibility displayed visibility value will be 5000 and the output can be:
amb=+050 alfa=+0.0000 vis=5000

Some short data of the MiniBSVDimensions（W*D*H）

68*34*45 mm

WeightAbout 170 g

Warm up time

About 1 minute

Current consumption<50 mA DC12 Volt ( 8-14)

Outputs

Analog 0-5 V, Digital RS232

Update time

30 seconds

Operation Temp. range-20 to +50 ℃

Optical output power

About 3 mW (NIR LED) eye safe, class 1 M

Wavelength

850nm

Housing

Anodized aluminum, opening sealed with -rings

Visibility range

20m – 4,000m

Relative maximal error for MiniBSV visibility sensor versus
visibility

Example1:
When the visibility is 100 meters the error may vary from +0.35 to -0.21,
which means that the displayed result may vary between 79 to 135 meters.
Example2:
When the visibility is 1000 meters the error may vary from +0.4 to -0.22,
which means that the displayed result may vary between 780 to 1400 meters.

Mounting
The sensor should be mounted so that it "looks" horizontal and roughly north (southon the southern hemisphere) – minimizing sunlight into receiver. There must not beanything in the sightline closer than 5 to 10 meters. Outside a cone of about 30
degrees angle objects can be tolerated at down to 2 about meter. See figure below.

The outer dimensions are 68*45*34 mm and the four M3 holes for fastening arelocated on the top surface on a centered rectangle 14*51 mm.
We deliver a mounting bracket –seen in picture above - made of PMMA plastic. The
picture shows our solution for mounting on a vertical 42 mm dia. tube. The sensor
is electrically isolated when using this mounting bracket.
Mounting on a wall or too near to a roof of a building is not recommended. The
reason is that the air near a building is a little warmer than some meters away fromit. And in the warmer air the small “drops” will evaporate resulting in a higher
measured visibility not representative for the visibility in the area.
The sensor is delivered with a 6 meter 5-wire cable connected. The wire colors arechosen as follows:

redblack
whitegreen
yellow

12 Volt DC Power inPower ground
Signal ground
Digital signal out
Analog out