Fan Unit (Fan320); Functional Description - Alcatel 1850 TSS-320 Technical Handbook

4.4 Fan unit (FAN320)

In the 1850 TSS-320 equipment two FAN units are mandatory.
The unit can be simply plugged into the backpanel as any other board of the 1850 TSS-320, in one of the
two slots present for the purpose, at the top and at the bottom of the shelf.
Fan speeds are monitored through Spider block, that also collects alarms rising when fans revolve below
30% of their maximum speed allowed.
The fan unit is set up with a basic assembled pcb on which fans are screwed on; on the same pcb the
fan controller is also hosted.

4.4.1 Functional description

The fan controller is the pcb dedicated to providing fans with power, managing the speed of each of them
and monitoring speeds through Spider block, that also collects alarms rising when fans revolve below 30%
of their maximum speed allowed.
Each fan is powered by 48Vdc voltage, supplied through a 38V-75V input acceptable range DC/DC
converter.
On the power supply of each fan a fuse has been inserted, so that if a rotor had to be blocked for any
reason, the current absorbed from it would rise and then the fuse would break, protecting the motor from
damages.
In reality, this caution is not strictly necessary, since fans mounted on the unit have themselves a locked
rotor protection: if the rotor is prevented from rotating and power is applied to the unit, the motor will self-
protect. When the locked rotor condition is removed the fan will automatically restart. The motor can
sustain locked rotor conditions indefinitely throughout the full specification range of voltage and
temperature.
Figure 113. on page 177 shows the block diagram of the unit.
As we can see, Spider can individually interrupt the 48V power supply of each fan, detects temperatures
from three sensors spread across the controller board and can adjust fan speeds by means of three
potentiometers, which provide through potential dividers variable voltages to fan speed control pins.
The speeds of three brushless DC motors are also monitored. Is available an output signal that switches
at a frequency of 2 cycles per revolution of the fan: when the fan is not rotating, the output is either a steady
High or a steady Low. This signal enters a monostable that detects the presence of it and refers to Spider.
At the same time, it enters a counter triggered by a 1 Hz sync (SY1Hz) coming either from matrix A or B
(and selected by ACT lines): information about revolutions is so collected every 1 sec and read by Spider
by means of an enable command.
On board a bicolor led is present to show:
green: unit in service
red: internal fault (unit out of service)
The FAN unit front panel is shown on page.
Technical Handbook Common
Unit Descriptions
Alcatel 1850 TSS-320 Rel. 1.1
8DG 07734 AAAA Edition 01 175/270