Table of Contents
Advertisement
The Alarm Card contains a pair of form C relays to provide shelf PMN and PMJ isolated closures. The
relays are energized, from both the A & B input bus, in their non-alarmed state, such that these relays
will revert to the alarm state if both A and B input fail. 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 deenergizes the relay. 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. While an active PMJ is present
the Alarm Card ignores the state of the PMN bus (and does not assert a PNM relay/LED action). This
IS necessary since the same 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.
The Alarm Card shall also monitor its internal I2C to RS-485 conversion processor. A failure of this
processor shall constitute a PMN condition.
Page 61
© 2021 ABB. All rights reserved.
Advertisement
Table of Contents
