OMC-183-ML Manual
Page 14
3.3.
User settings QNH & QFE
Calculation of the QNH & QFE is required when the meteorological station is used for helideck or
runway monitoring. QNH is the barometric pressure at sea level, while QFE is the barometric
pressure at helideck (the same applies for a runway).
For this calculation the height of the helideck above sea level is required as well as the height of
the barometric sensor above the helideck. These values will be negative if they are below sea
level or helideck.
The height of the barometric sensor above the helideck will be set in variable S1, this value will
be negative when the sensor is below the helideck.
The height of the helideck above sea level will be set in variable S2, this value will be negative
when runway is below sea level.
According to the CAP-437 barometric pressure must be measured with a minimum of 2 sensors
placed at the same location. These Dual barometric sensors have been implemented in the
OMC-183-ML according to the CAP-437. One important implementation is output messages:
First when the difference between the two sensors is >0.5 hPa, no data should be presented.
In this case no barometric information messages will be send by the device.
In the OMC-2900 format an additional status message of the Barometric sensors is included:
S0 = Normal operation of dual barometric sensors
S1 = Sensor 1
Error or out of range (threshold settings)
S2 = Sensor 2
Error or out of range (threshold settings)
S3 = Sensor 1 or 2
Error or both out of range (threshold settings)
S4 = Maximum deviation of barometric pressure > default 0.5
Always use the height of the location of the barometric sensor itself, even if a pressure head
(OMC-509) is used. The location of the pressure head is irrelevant for the sensor height!
The sensor is preferable build in the same housing as the OMC-183-ML.