HR
X
-C-HB-1
C-B
AND
L
INK
H
ANDBOOK
12
2.3.5
Connecting to the summary alarm
The alarm output pin should be connected to a suitable current source (a positive voltage via a 10kohm
pull-up resistor is adequate). When the module is in a working (non-alarm) state, the alarm output pin
is short circuited to ground by the module. If the module enters an alarm state, the alarm pin is released
to a high impedance state and current is no longer drawn from the constant current source. In the case
of a positive voltage and pull-up resistor, the voltage on the alarm output pin will rise to indicate the
alarm state. It follows that, if a module is removed from the chassis, the alarm will be raised for that
module position.
The capability of the open collector is dependent on the module that provides it. The typical capability
of the Open Collector/Drain is 50mA maximum current sink and 15V maximum voltage (Vext).
Note: Modules fitted in a chassis may have their alarm lines pull up by other chassis equipment, such
as switch, splitter, summary alarm or SNMP and web controller modules.
2.3.6
Received light level (RLL) alarm
Receiver modules, monitor the average incoming received light level (RLL), if the power drops below
a pre-set threshold the module will generate an RLL alarm.
The RLL alarm threshold is set for a nominal input power of -15.0dBm
o
Nominal optical loss of 25.0dB @ 10.0dBm (10mW) TX
Under normal operating conditions the RLL alarm accuracy is +/-2dB; and +/-4dB under extreme
conditions.
2.3.7
Module analogue monitor
Each plug-in module has either one or two analogue monitor ports. These allow simple DC indication
of the status of either lasers or photodiodes fitted in the RF modules. The analogue monitor is available
on the chassis connector, see the chassis handbook. The analogue monitor functions are dependent
on the type of module. The monitor function(s) provided are shown in the table below.
Function
Single Transmitter
Single Receiver
Analogue monitor A
Not Used
Received light level
Analogue monitor B
Laser bias monitor
Not Used
Vext
Pull up
Resistor
Alarm
Ground
Internal to module External to module
