4 PRINCIPLE OF OPERATIONS
9070
4.3 TRANSMITTER
UNIT
4.3.1 ELECTRONICS
CHASSIS
The chassis contains three circuit boards:
9
Digital Board
- Behind the faceplate, containing the central
processor unit, front panel controls and the display.
9
Analog Board
- Middle board, containing the analog input and
current output circuitry.
9
PSU Board
- Rear board, containing the power supply and
output relays.
4.3.2 CIRCUIT BOARD FUNCTION
The microprocessor senses a series of eight “ON/OFF” switches in a dual-in-
line package, and provides controlling functions for the alarms, output current
and calibration - see Table 4.2.
FIGURE 4.2 CIRCUIT BOARD FUNCTION SWITCH
16
