Service Manual

GSM-205-323
Indoor temperature control system
31st Oct 01
Technical Description: Horizon macro indoor
68P02902W07-B
CONTROLLED INTRODUCTION
Tech. 3–1
Indoor temperature control system
Temperature
control
overview
The Horizon macro indoor cabinet contains equipment that has to be maintained
within the operational temperature range, to ensure correct operation of the
equipment and to guard against premature failure of the individual components.
The internal temperature is maintained within these limits by internal fans.
Cabinet over
temperature
control
Under overheat conditions, as the temperature rises above preset levels,
temperature sensors located in various areas within the cabinet provide alarms.
A further increase in temperature causes dual sensors, set at a higher threshold
temperature to initiate PSM and cabinet shutdown. The cabinet is restarted
when the sensors are reset by a substantial fall in temperature.
The CTUs have their own shutdown responses to overheating. The CTUs
shutdown at 92 C.
850/900 MHz CTUs also have an internal 4 dB power reduction response to
overheating at 85 C. 1800/1900 MHz CTUs have a 0.6 dB cut back at 70 C, in
addition to the 4 dB power reduction at 85 C.
The CTU shutdown response to overheating provides a second level of cabinet
protection, independent of the cabinet heat sensors.
Temperature
sensors
The three cabinet temperature sensors are located above the CTU
compartment (see Figure 2-7) and consist of the following:
 One 70 C sensor provides a cabinet overtemperature alarm when the
cabinet temperature exceeds planned level. The alarm is processed by
the alarm board and MCUF, and sent on to the OMC-R via the BSC.
 Two 85 C sensors shut down the PSMs to protect the cabinet equipment
from heat damage. Both sensors must detect excess temperature for the
shutdown to take place; this reduces the risk of an unnecessary shutdown.
No prior notification of shutdown is given to the OMC-R, except for the
original 70 C sensor alarm. This is because the MCUF and CTUs
immediately lose power and functionality.
Cabinet restart
after shutdown
The cabinet is restarted when the overtemperature condition initiating shutdown
has reset. The two 85 C temperature sensors reset at 55 C. This
re-establishes an earth point for the PSM internal detectors connected to the
cabinet heat sensors, which then reactivate the PSM outputs. The MCUF then
reboots as in a normal power up.