Comtech EF Data SMS-458B - Manual (Page 70)

SMS-458B Modem Protection Switch Revision 2
Theory of Operation MN/SMS458B.IOM
4–10
4.1.5.1 Controller Fault
A controller fault is a catastrophic failure that renders the switch nonfunctional. A timer
on the M&C periodically sets a monostable, which controls the fault relay.
The controller fault relay NC and COM contacts close when:
• No power is applied to the switch.
• When the M&C fails to set the monostable.
During normal operation (when no fault occurs), the relay NC and COM contacts are
open and the NO and COM contacts are closed.
4.1.5.2 M:N Fault
An M:N fault is any failure of backup operation, communication, configuration, and/or
setup that may (or may not) render the switch nonfunctional.
During normal operation or power-off, the relay is de-energized (COM to NC). When
any failure occurs, the relay energizes (COM to NO). It remains energized until the
failure is eliminated.
4.1.5.3 Demodulator Signal Fault
A demodulator signal fault is the failure of all active demodulators on the indicated
downlink to acquire and lock to their signals. The fault alarm indicates a possible down
converter system failure causing loss of IF to the demodulators. During normal operation
or power-down, the relay is de-energized (COM to NC).
When all demodulators indicate loss of carrier, the relay energizes (COM to NO). The
relay remains energized until the failure is eliminated.
4.1.6 Online Status Specification
This section defines the protocol and format for reporting the online status of the switch.
The M&C commands the online telemetry module to report online status for all active
prime modulators and demodulators. The status is reported as form-C relay contact to the
online status connectors (J4 and J5) on the rear panel (see Section 2.2.4 for connector
locations and pinouts).
The active modulators online status is indicated at J4 by form-C relay contacts. When the
prime is online or power is off, the relay is de-energized (COM to NC). When a backup
modulator goes online for that prime, the relay energizes (COM to NO).