Temperature Sensors; Cooling Unit Led Indications - Nortel Passport 15000 Hardware Description

134 Chapter 3 Shelf assembly

Temperature sensors

Cooling unit LED indications

241-1501-200 5.2S2
A set of three temperature sensors monitors exhaust air flow from each of the
cooling units, as shown in the figure "Upper and lower cooling unit in a frame
with air flow direction" (page 130). The sensors for the lower cooling unit are
inside the unit itself, while the sensors for an upper cooling unit are on a
sensor bracket assembly that is mounted in the air flow space above the shelf
assembly. Each temperature sensor is mounted on a PCB. The temperature
sensors are not linked directly to a specific fan and can monitor the air flow
generated by multiple fans simultaneously.
The temperature sensors are linked to a temperature interface block, which
provides bias to the sensors, monitors faults in the sensor circuit, and
processes temperature information. If a temperature greater than 72 degrees
Celsius (162 Fahrenheit) is detected, a HighTemp alarm is sent to the alarm/
BITS module where the alarm is indicated. When a temperature less than
55 degrees Celsius (131 Fahrenheit) is detected, the fans operate at normal
speeds. If a temperature between 55 and 72 degrees Celsius is detected, the
fans switch to high-speed operation.
A built-in hysteresis prevents the fans from continuously toggling slower and
faster at the temperature threshold.
Each cooling unit is equipped with LEDs to indicate its status. The table
"Cooling unit LED indications" (page 134) lists the possible LED displays.
Table 19
Cooling unit LED indications
LED Description
Green on The unit is on and no fault is detected.
Red on A fan fault has occurred: missing at least one fan or at least one
temperature sensor has failed. A FANFAIL signal is sent to the
alarm/BITS module, and the remaining fans are switched to the
high speed setting.
None on The middle circuit breakers (for the cooling units) on both BIMs
are switched off or there is no power to both BIMs for that shelf.