TESTO 645 - Measuring Absolute Pressure

Absolute pressure is calculated from:
• Elevation pressure (metres above NN)
The annual mean is 1013 mbar at sea level, the higher the
location above sea level, the lower the pressure.
• Barometric pressure
The annual mean is 1013 mbar regardless of height. This
pressure can deviate from the annual mean by ±20 mbar
depending on the weather (see display on nearest barometer).
• Differential pressure
is the positive or negative pressure in the duct.
You can determine the annual mean air pressure value for your
elevation using the following table and any additional fluctuation
using a barometer or ask your weather station for the exact air
pressure value.
31
Measuring absolute pressure
Table: Barometric elevation formula
Elevation
M.S.L
Elevation
M.S.L
Air pressure
(mbar)
Air pressure
(mbar)
Air pressure
(mbar)
Air pressure
(mbar)
Elevation
M.S.L
Elevation
M.S.L
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