The output is presented in digital form as an ASCII string on the RS232 output, 2400 baud 8N1, that is transmitted "streaming" every 5 minutes. 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 Hyper Terminal (part of WINDOWS).This is an example of an output string:
09:24:16> 0.00196 01530 0.00000 0.21100 0.00000 -00006 000120 71
The number before the ">" character is a time stamp made by the terminal program used.
The second number - in this case 0.00196 - is the extinction coefficient often called alfa. The relation between the extinction, alfa and visibility, VIS, is alfa=3/VIS. The alfa parameter can be used for monitoring trends in visibility when the visibility is larger than 5000 meters. But note that the absolute accuracy in alfa is limited in such cases.
The third number is the measured visibility in meters, if the measured visibility is larger than 5000 meters 05000 is displayed.
The fourth number is a measure of the rain precipitation in mm/h during the last 5 minutes.
The fifth number is the same for snow.
The sixth number is the same for mixed precipitation.
The seventh number is the temperature inside the sensor casing. The accuracy of this number as a measure of the ambient temperature is
something like ± 3 degrees or even higher during sunlight.
The eighth number is an uncalibrated measure of the ambient solar irradiance. The sensitivity depends stongly on how the sensor is aimed. It may vary considerably. But the the repitivity is much better and the offset error is only ± 2 units. The sensor can, when mounted, be individually calibrated by comparing it with an irradiance sensor. But a simple method is to take data from a clear 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 useful for instance for telling if it is day or night.
The ninth number in the data string is WMO codes.
00 is for good visibility, no precipitation
10 is for light fog, visibility between 3000 and 1000 meters
30 is moderate fog, visibility < 1000 meters
61 is for light rain
62 is for moderate rain
63 is for heavy rain
68 is for light intensity of mixture of rain and snow
69 is for light intensity of moderate or heavy mixture of rain and snow
71 is for light snowfall
72 is for moderate snowfall
73 is for heavy snowfall
The sensor is delivered with a PMMA plastic mounting bracket, see picture to the right above. An important advantage with this bracket is that it isolates the sensor electrically which reduces the risk for surge currents during lightning etc.
The sensor is heated a little above ambient temperature in order to keep moisture away.It is delivered with a 6 meter 5-wire cable connected.
In order to keep the electronics dry a there is membrane ventilator that keeps the pressure inside at the same level as outside. This prevents liquid water from sucking into the sensor through micro cracks etc at falling temperature - a creative solution to a big problem....
The sensor should be mounted so that it "looks" roughly north (on the southern hemisphere south). There must not be anything in the sightline closer than about 5 meters. Outside a cone of about 30 degrees angle objects can be tolerated at down to about 1 meter.