Vaisala FD12P - Manual (Page 22)

User's Guide _______________________________________________________________________
22 ______________________________________________________ M210296en-A
The output of the DRD12 is proportional to the water amount on the
capacitive sensing surfaces while the optical intensity is proportional
to the total volume of the reflecting particles. The ratio of optical and
capacitive intensities is used to determine the basic precipitation type.
The crossarm temperature (TS) is measured with the DTS14B
Temperature Sensor connected to the DRI21 interface card. The
temperature data together with the optical signal profile and the
DRD12 surface sensor data are used to determine the actual weather
code.
The software performs all signal analyses in the FD12P except the
DRD12 Rain ON/OFF status, which is hardware-based and is used as
an auxiliary parameter. The FD12P has a fixed program that is divided
into tasks executed under control of a real-time operating system
kernel. Each task is like an endless loop with a limited function. The
operating system kernel controls the timing of the tasks and the
interactions between the tasks.
Using FD12P
The FD12P is typically used as a component of a weather observing
system. The final weather message (SYNOP, METAR) is then coded
in the central unit of a weather observation system (for example,
Vaisala MILOS 500) or by a human observer using the FD12P as an
observation aid.
The FD12P output is a digital serial interface, which can be
configured into two different operating modes: the sensor can be set to
send a data message automatically at selected intervals, or the FD12P
can be polled by the host computer. The same serial line is also used
as an operator interface.
The operator controls and checks the operation of the FD12P by using
a maintenance terminal. A set of built-in commands and test routines
is provided for configuring and monitoring the multiple functions of
the FD12P.
The standard data messages contain a status character for indicating
faults detected by the internal diagnostics. If the error status is set, the
operator can view a special status message. It contains detailed results
of the diagnostics and a written description of the fault. Using this
information, the operator can take corrective action or provide the
maintenance personnel with valuable advice.