GP941E 11/01
02.11.01
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11. Calibration chart for altimeter of GP941:
According to FAI rules an altimeter calibration chart of the recorder must be used for altitude evalua-
tion of recorded flights.
If altitude differences are relevant to a claimed flight, the calibration chart must not be older than two
years or a calibration must be done within one month after the flight. Altitude differences are impor-
tant for all flights, where the difference between release altitude and landing altitude is not much less
than 1000m and for altitude gain flights.
If absolute altitude is concerned, the calibration chart must be not older than two years and a calibra-
tion must be done within one month after the flight. This is important only for absolute altitude world
records.
The calibration chart can be done by the manufacturer of the recorder or by any institution certified by
the national aero club.
To get an altitude trace of the GP941, the recorder must be put into a vacuum chamber and be
suplied with 12V / 120mA (minus = pin 2, plus = pin 5 of 9 pin plug at the rear of the box besides the
antenna connector - see 10. Pin assignments of connectors ). The GPS antenna is not connected.
When power is applied the GP941 starts recording. Now the ambient pressure is changed in steps
from 0m to 10000m. As the recording rate of the GP941 is one sample every four seconds, the am-
bient pressure should stay enough stable at each step to get a good reading. Maximum calibration
altitude is 10000m.
If it can be managed to operate the marker switch from the outside, the altitudes can be marked with
one second acuracy. These marks can easily be found later in the data file for evaluation.
After all altitude steps were recorded, a PC can be connected to the 9 pin socket at the front besides
the red light. Recorded flight data are read by DATA-ZAN.EXE.
Flight data can be converted to IGC format by CONV-ZAN.EXE. The IGC file is an ASCII file where
altitude readings can be found easily. If the marker switch is used, the altitude belonging to the mark
is always the next reading after the mark. Each B line represents a reading:
B hhmmss ggmm.ddd N gggmm.ddd E V hhhhh ggggg iii nnn rr
(hhmmss = time, hhhhh = altitude reading)
