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16. Typical thermal characteristics.
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The graph above illustrates the expected average internal temperature versus the external ambient temperature for
the passive temperature specification. The external ambient temperature is defined here as the temperature of the air
being drawn into the heat exchanger on the underside of the Lidar. Depending upon the characteristics of the ground,
this may be hotter than the temperature as measured in the conventional way for meteorological reporting.
Systems fitted with the thermo-electric cooler (TEC) referred to as the extended temperature option.
The heat exchanger fans will be on all of the time, and as soon as power is applied to the Lidar, as the cooling system
is not covered by the power cut protection circuit, and has its own fuse (F2). The TEC unit will try and hold the internal
temperature of the Lidar at 25˚C. It will offer both active heating and cooling, and draw an extra 130W of power when
fully cooling and an extra 60W when heating.
System fitted with the extended temperature option with an additional set of TEC elements.
This configuration allows the units to be deployed in ambient temperatures up to 50˚C. The extra TEC elements will be
powered from the power cut protection unit, with an additional blade style fuse being housed inside.
Thermal shutdown.
In the event of a cooling system failure, or high ambient temperatures (> 42˚C), the software will shut some parts of
the Lidar down. Data collection will be paused while the system is in this thermal shutdown mode. A notice will be
displayed on the system information window, 'Thermal shutdown – waiting for the internal temperature to reduce', and
an event will be written to the system error log.
When the temperature is back to an acceptable level (normally 5˚C lower than shutdown temperature set point), then
the system will resume taking data as normal.
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