We plan to install a barometer at the top of the met mast (e.g. 80 meter). What do we need to take into account?

This depends on the type of barometer. If you use the e.g. Setra M276 sensor (output in voltage) you need to increase the cable section from 0,5mm2 to 2.5 mm2 to avoid signal loss.

Unlike most other barometers the frequency output from the K611P barometer however ensures signal integrity from the top of the met mast all the way down to the data logger at the bottom. You do therefore not need to increase the cable section when using this sensor. The K611P barometer is therefore, in most cases, the most cost effective overall solution (saving you costs on cable).