1264C User Manual
Voltage Monitor
The VXI voltages are routed to the monitor board from the
backplane through the 14-pin ribbon cable. The voltages are
scaled and inverted (negative supplies only) and routed to the
window comparators. The window comparator thresholds are set
to detect that the supply is within
±
10% of nominal. A 2.5V
reference is used to establish the window comparator thresholds.
The reference can be adjusted via potentiometer R148 while
measuring the voltage between J4-1 and J4-4 (GND). If the
respective supply is with limits the front panel LED is Green. The
LED will illuminate Red if the supply is out of limits.
Fan Monitor
The fan monitor verifies that the fan is delivering cooling air by
measuring the voltage difference between two self-heating
thermistors. The ambient thermistor RT2 is isolated from the fan air
stream. The air flow detecting thermistor RT1 is in the air stream.
When the fan is operating properly the front panel LED is Green.
The LED will illuminate Red if the fan is not operating.
Temperature
Monitor
The power supply intake air temperature is monitored by sensor
U11. The sensor generates a voltage (500 mV + 10 mV/
°
C). The
temperature monitor comparator is set to generate a fault (Red
LED) at 60
°
C (or 1.10V).
ACFAIL* and
SYSRESET*
Signals
The monitor board receives the Power Fail signal from the PS1
supply at J2-1. From this signal the VME signals ACFAIL* and
SYSRESET are generated with the appropriate timing relationship
– see the VME specification revision C-1, or later. The signals are
then routed to the backplane through the 14-pin ribbon cable
between J1 (monitor) and J50 on the backplane.
Understanding The 1264C 4-6
EADS North America Defense
Test and Services, Inc. © 1998
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