Chapter 5 _________________________________________________________ Theory of Operation
VAISALA _______________________________________________________________________ 139
Controller Board FSC102
The Controller Board consists of a microprocessor, a communication
interface, temperature measurement circuitry, a watchdog, memories,
monitoring circuitry, and heater controllers.
The Controller board is based on a Hitachi H8/3048F microprocessor.
Besides data acquisition and internal controlling, the FSC102 board takes
care of the communication with the communication controller through an
RS-485 serial port.
The watchdog circuit monitors both the +5 V level and the system
operation creating a hardware reset when necessary. The Controller
board further includes an accurate 20 bit A/D converter for Pt100
temperature measurement.
There are two separate sets of heaters in both the FSM102 Visibility
Measurement Unit and PWD32 Precipitation Identifier: Hood heaters in
the outside hoods of the optics heads, and dew heaters inside the optics
units for keeping the lenses clear.
The Hood heater control logic consists of two solid state relays. Both
hood heater foil elements are independently controlled according to the
temperature measurement on the heater foil. The hood heater voltage
level is 28 VAC. The dew heaters are controlled to prevent the formation
of condensation on the sensor windows. The dew heater voltage level is
13 VDC.
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