At what altitudes can PULS devices operate?

PULS devices can be used without restrictions up to a height of 2000 metres above mean sea level.

Above an altitude of 2000 metres, the output power must be derated, because the air pressure falls as the altitude increases. This means that the air becomes less dense, which also reduces the cooling effect of the convection air flow in the power supply.

Up to 2000 metres above mean sea level:
PULS devices are designed to operate without restrictions up to an altitude of 2000 metres above mean sea level. 

2000 to 6000 metres above mean sea level:
At altitudes between 2000 and 6000 metres above mean sea level, a derating of 7% per 1000 metres or a reduction in the permitted temperature range of 5°C per thousand metres is typically required. The exact derating figures for each device can be found in the relevant datasheet. Another option is the installation of a ventilation system in the cabinet. The overvoltage protection is reduced from category 3 to category 2.

More than 6000 metres above mean sea level: 
Devices should ideally not be operated at an altitude of more than 6000 metres above mean sea level because of the increased cosmic radiation.