ABB CPS2400U Product Manual page 53

Alarm Card Logical Operation of LEDs and Alarm Relays
The Alarm Card contains a pair of form C relays to provide shelf PMN and PMJ isolated closures.
Both PMN and PMJ relays will signal alarm if both A and B input fail. Relays coils are energized to signal
normal (no-alarm) and are redundantly powered by both the A & B input buses.
The relay circuit interfaces to a pair of parallel buses connected to each of the 16 Converter/Limiter
Cards. Each Converter has an open collector output on the bus, and pulls the bus low to chassis ground
when it is asserting an alarm. The PMN/PMJ circuit on the Alarm card recognizes the bus state change
and denergizes the associated alarm relay, signaling alarm. The alarm card separately monitors both
the PNM and PMJ bus. When the PMN bus is active (pulled low), the Alarm card asserts a PMN relay and
lights the ALM LED Yellow. When the PMJ bus is active (pulled low), the Alarm card asserts a PMJ relay
and lights the ALM LED Red.
The Alarm Card ignores the state of the PMN bus (and does not assert a PNM relay/LED action) while
an active PMJ is present. This is necessary since a single LED is used for both Minor (Yellow) and Major
(Red) visual indication.
The Alarm Card also monitors the -48V dc inputs and asserts PNM/PMJ for conditions as described in
the earlier section dealing with input voltage monitoring.
The Alarm Card also monitors the two fan tray alarms. When either of the two fan tray alarms is active,
the Alarm Card asserts a PMN relay and Yellow ALM LED. When both of the fan tray alarms are active,
the Alarm Card shall assert a PMJ relay and Red ALM LED.
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The Alarm Card shall also monitor its internal I C to RS-485 conversion processor. A failure of this
processor shall constitute a PMN condition.
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