Environmental Engineering Reference
In-Depth Information
switch amplifiers and controls the fuzzy logic for the heater. From the microprocessor
the signals are routed to the COM port of the host computer using the RS 232 protocol.
Cable lengths of up to 150 m can be used without any deterioration of the signal. Longer
transmission lines without cross talking are possible by using the RS 485 protocol.
The components of the instrument are housed in a 6 mm welded PVC case with
an internal and external metallic shielding and a 12 mm Styrofoam thermal insulation.
The instruments are flooded with dry nitrogen and hermetically sealed with a 10 mm
Plexiglas top which carries the optical head. The underwater instruments have
additional measures to keep them hermetically sealed. They are bolted on heavy rocks
or concrete slabs and have been shown to withstand even strong currents during winter
storms. The underwater instruments have no internal temperature control since the water
mass around them limits the temperature range. A third type of instruments (dive
version) is designed to determine the light gradients in three channels and the
temperature in dependence of depth as the instrument is lowered into the water column.
From these data the attenuation coefficients can be calculated for each of the three
radiation channels.
4. Software
The software package WinDose 2000 for the ELDONET instruments has been
developed in Visual Basic (Microsoft, Redmond, WA, USA) and runs under the
Windows platform. When the program is started, it tests the available serial ports for the
presence of an ELDONET instrument. The instrument answers by sending back its
unique code number which also defines whether it is a terrestrial or aquatic instrument
or a dive version. Before the first measurements commence at a new location the
geographic coordinates for longitude and latitude and the site name are entered. The
calibration requires the knowledge of the solar angle. Therefore the program determines
the solar angle from the longitude and latitude data and the time and date provided by
the host computer. In order to warrant high precision measurements the time should be
as accurate as possible. The computer hardware clock can be automatically updated by
programs on the net when the computer is connected to the Internet. Internally the
software calculates in Universal time and Windows provides the offset to the local time
as well as the shift from daylight saving to winter time and back, so that the local time
can be displayed on screen. The measurements start in the morning when the sun is 12°
below the horizon and end when it sinks 12° below the horizon. This condition may not
be met when the instrument is located near one of the poles. The geographic data, the
individual number of the instrument, the name of the location and the calibration data of
the specific instrument are stored in an individual initialization (.INI) file.
The microprocessor within the instrument sends updated values once every
second to the host computer where they are displayed in numerical and graphical form.
In addition, it sends averages over one-minute intervals which are stored in a disk file
which is updated every 15 min. The main screen shows the radiation and external
temperature data in graphical as well as in numerical form together with the doses
accumulated since the start of the program for the day. For the aquatic instruments the
water depth is displayed. A toolbar allows to display selected data, print them or store
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