Service Manual

GSM-204-323
Thermal management system (TMS)
31st Oct 01
Technical Description: Horizon macro outdoor
68P02902W02-A
CONTROLLED INTRODUCTION
Tech. 3–5
TMS functional
description
The TMS unit provides either cooling or heating to maintain the internal
temperature of the Horizon
macro outdoor BTS cabinet within the operational
range of the installed equipment. The TMS temperature sensors measure the
temperature of the returned recirculation air from the cabinet equipment
enclosures.
Cooling
The TMS employs an indirect cooling system to protect the radio equipment
against atmospheric contaminants. Cooling is provided by recirculating air
through two air to air heat exchangers. Two separate airflow paths are driven
through the two recuperators by fans; the warmer air stream gives off heat to
the colder air stream.
The TMS control board manages the speed of both sets of fans. The control
board initiates an increase in fan speed when either TMS temperature sensor
detects an increase in temperature, above a control threshold. A reduction in
fan speed is only achieved when both sensors detect a decrease in temperature
below the control threshold.
The recirculation air fans run continuously. As the temperature rises, the
ambient air fans start. A further temperature rise causes both fans ramp up to
full speed.
The recirculation air fans run at 60% of full speed at all temperatures, up to
55 °C. Fan speed increases linearly as the temperature rises, until it reaches full
speed at 60 °C.
The ambient air fans are inhibited at temperatures below 40 °C and run at 60%
of full speed between 40 °C and 55 °C. Fan speed then increases linearly as the
temperature rises, until it reaches full speed at 60 °C.
Heating
At low temperatures and in cold start conditions, ac electric heaters are used to
maintain the cabinet internal temperature at operational levels. Only the
recirculation air fans operate when the TMS is heating the cabinet.
Heater element operation is managed by the TMS control board. The control
board switches the heaters on when either TMS temperature sensor detects a
decrease in temperature to below 10 °C, but only switches the heaters off when
both TMS temperature sensors detect a corresponding rise in temperature to
above 20 °C.
Heater function is indicated by the illumination of an LED, mounted on the rear
verical wall at the top right of the recirculation air outlet aperture, below and in
front of the power supply enclosure.