GARD – Installation, Operation and Maintenance Manual
A l e n c o n S y s t e m s L L C - P a g e
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5 Firmware
All of the GARD’s control tasks are executed by the firmware stored in the microcomputer memory
mounted on the GARD’s main PCB. The program is constructed as a
“State Machine”
.
5.1 GARD State Machine
The GARD’s “
State Machine”
contains seven main states. The control transition from state to
state is shown in Figure 9.
INITIALIZE:
Upon power up, or receiving a SHUTDOWN, RESET, CLEAR_FLAGS or
TESTMODE command, the GLID/AFD enters the INITIALIZE state. In the INITIALIZE state,
the MCU resets and checks for the fault flags. If the flags SHUTDOWN or TESTMODE are
not set, the microprocessor proceeds into the STANDBY state.
STANDBY:
In the STANDBY state, the microprocessor checks that the control voltages
and all the sensors are in operating range and then proceeds into a SELF-TEST state.
SELF-TEST:
In the SELF-TEST state, the microprocessor performs a set of self-tests that
essentially check the quality of the GARD sensors i.e. current sensor.
CT Check
– GARD injects a current into the circuit that flows through the negative current
sensor. This difference should simulate a current fault. If any of the channels fail to detect
the
“simulated fault”
they will be disconnected and a fault flag will be recorded in the
GARD’s non-volatile memory (NVM). If at least one channel is found to be good the
microprocessor proceeds into PRECHARGE state for that commensurate channel.
AFD_self_test –
A sample arc signature is generated during self-test and the AFD board
reacts to the sample signature and a flag is generated. This is a self-evalution that must
pass prior to the relays closing.
PRECHARGE:
In the PRECHARGE state, the GARD pre-charges the capacitors available
on the output for a dedicated time period defined by the configuration file. In this state, the
relays on the negative terminal are closed, while the open contacts are bypassed by a “soft-
start” resistor. This feature preserves the life of relay contacts. Once the load capacitors
are charged, the relay on the positive terminal is closed. When the PRECHARGE process
is complete on all four channels the microprocessor proceeds into RUN state.
RUN:
The RUN state is the main state of the GLID/AFD. In RUN state the microcontroller
is looking for a ground leak fault.
Ground leak: T
he leak-locator hardware on the board helps indetifying groundfault before
the relay contacts close.
