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Combo — Manual 6. Sensor Calibration
6 Sensor Calibration & Altitude Calcu-
lation
6.1 Calibration Procedure
Each unit is factory calibrated against reference barometer at dif-
ferent pressure points. In standard calibration range we calibrate in
following pressure sequence: 1100, 1000, 900, 800, 700, 600, 500, 400,
280, 550, 650, 750, 850, 950 and 1050 hPa. These measurements are
then repeated at different temperatures ranging from -10 to 60
◦
C in
7
◦
C steps.
Please note that FAA Part 43, Appendix E does not require calibra-
tion/verification at different temperatures. But temperature calibra-
tion is essential for any electronic sensor.
This means that each instrument is calibrated against 13
·
11 = 143
different temperature - pressure pairs. The least squares method is
then applied on this results in order to obtain corrections coefficients.
A two dimensional, third degree polynomial is used for the correction
model.
You can’t change calibration parameters, but you can adjust the
altitude. Please refer to the section 3.1 for more details.
6.2 Pressure Altitude Calculation
Pressure altitude is calculated according to the ISA 1976 model of
athmosphere. First two athmosphere layers are used; throposphere
and thropopause. The throposphere is modeled by equation (1) up
to 11000 meters of geopotential altitude. The thropopause layer is
modeled by equation (2) up to 20000 meters of geopotential altitude.
As the pressure sensor is calibrated down to 100 hPa (about 16000
meters) altitudes above 16000 meters are not reliable.
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