Startco Engineering Ltd.
Page 35
FPU-16 Feeder Protection Unit
Rev. 1
Pub. FPU-16-M, November, 1997
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5.
THEORY OF OPERATION
5.1
GENERAL (See Figure 14)
A basic FPU-16 consists of a display module, a power-supply module, a
processor module, and an analog module.
The display module is a
"motherboard" for the other modules.
5.2
DISPLAY MODULE
The display module has two functions. It is the operator interface and it provides
the main bus network for the system. The display module contains the LCD,
LCD driver, LED indicators, and bus connectors. The power-supply, processor,
analog, and option modules plug into the bus connectors. A sealed-membrane-
switch keypad containing four switches and an ESD shield also connect to the
bus. A direct-drive LCD allows operation to -40°C.
5.3
POWER-SUPPLY MODULE
A transformer-isolated power supply provides 5, 12, and 20 Vdc for the other
modules. The transformer primary can be connected for 120- or 240-Vac
operation. A dc-to-dc converter is used for 120/240 Vac/dc operation or for 12-,
24-, or 48-Vdc operation. The power-supply module also contains the trip-and-
alarm relays.
5.4
PROCESSOR MODULE
The processor module contains the CMOS 6805 microprocessor, EPROM
memory, nonvolatile EEPROM memory, and watchdog circuit.
The EEPROM memory provides 64, 8-bit memory locations to store programmed
values and values-at-trip. When the supply voltage drops below its minimum
rated value, a power-fail circuit generates an interrupt and data are written into
the EEPROM memory. Hysteresis in the power-fail circuit ensures that the
FPU-16 will not attempt to operate unless the supply voltage is within
specifications.
The watchdog connected to the CPU reset line will reset the CPU if a watchdog
pulse has not been detected for 0.25 second. The watchdog prevents changes
to the EEPROM contents until the CPU is reset. If the CPU does not reset, the
trip-and-alarm relays are de-energized and the green PROCESSOR LED is
turned off.
