DESCRIPTION AND OPERATION
MACHINE FAULT TIMER
I-E96-206A
2 - 7
MACHINE FAULT TIMER
A Machine Fault Timer (MFT) generated on board the AOM is a
security feature common to all microprocessor based INFI 90
modules. The timer is reset periodically by the microprocessor.
If it is not reset within a set time, the timer times out causing
the module to shut down (
time out
)
. It is reset on power up or
by the manual reset switch accessed through the module
faceplate.
If a
time out
occurs, the front panel module status LED lights
red and all outputs go to zero (0 mA or 0 VDC).
NOTE: Pressing the reset switch causes the outputs to go to zero.
ON-LINE TESTS
When the AOM is first installed or after a reset, it conducts
on-line self tests to verify that its logic circuitry is operating
properly.
RAM Test
A RAM test consists of writing data to the RAM, and then com-
paring the data in RAM to the data that was written. If this test
fails, the microprocessor stops resetting the MFT causing a
time out
to shut the module down.
PROM Test
A PROM test computes a checksum of the PROM memory con-
tents. It then compares this checksum to the known check-
sum. If they do not match, the microprocessor stops resetting
the MFT causing a
time out
to occur.
If all tests pass, the AOM initializes all RAM memory locations
and begins to drive the outputs to the demanded position (i.e.,
sample/hold demand). It also sets the front panel LED to solid
green to indicate that the module is on-line and operating
correctly.
Other problems within the AOM can cause a
time out
to occur.
The microprocessor periodically resets the MFT preventing it
from ever timing out. If a condition exists for the AOM that
causes the microprocessor to fail or operate incorrectly, the
MFT will not be reset resulting in a
time out
.
STATUS LED INDICATOR
A front panel module status LED indicator shows the operating
state of the AOM. Circuits on the AOM determine the module
status and light the LED accordingly. It lights green to indicate
normal operation.
explains the indications and
explains corrective actions to take.
