Why do products have an altitude limit?
1 Altitude affects the cooling ability of the device. At higher altitudes, the reduced air pressure reduces the rate at which heat from the device can be dissipated to the surrounding ambient.
2 Products temperature rating assumes use at sea level. All specifications need to be derated at higher elevations. In particular, this would affect our operating temperature specification (assume lower temperature maximum).
3 For those devices which are safety tested - to UL 60950-1 or its equivalents such as EN 60950-1 or IEC 60950-1, the test report specifically states that the report is only valid up to 2000m (slightly less than 7000 feet), so if a valid safety certificate is required, then the device shouldn''t be used over 2000m elevation..
4 Aeroplanes are pressurized - so the altitude limitation does not apply. If a device is used in an unpressurized plane, then it would have to fly below 2000m, for the specification to hold true.
5 Devices are not rated for mountain shelters above 3500m, although at that elevation, it would also be quite cold, so heat dissipation would presumably not be as much of an issue.
6 If its in a pressurized or sealed chamber, then altitude becomes irrelevant.
7 No Digi devices are space-rated - although we would expect that if humans could tolerate the environment, then so would our equipment. Devices in space are exposed to higher radiation levels which are only mitigated by better shielding. Device operated by a human in space would still work - as the shielding would be expected to be present to save the human from radiation affects.
8 Altitude affects the heat dissipation capability of the heat sink and units in locations at 3300 ft (1000 m) above sea level must be derated. A common rule of thumb is a 2% derating for every 1000 ft above the 3300 ft altitude level.