September 2012
3.4.1 QNH OR BARO (BAROMETRIC PRESSURE)
The altitude encoder outputs a pressure altitude fixed at an above mean sea level (AMSL) pressure of 1013mb
or 29.92Hg. The aircraft’s altimeter however is normally adjusted for actual surface pressure before take off.
This means the encoder altitude may not be the same as the altimeter reading.
The QNH / Baro can be entered here to allow the T2000SFL to compensate the displayed altitude for surface
pressure, and hence read the same as the aircraft’s altimeter. The default QNH is 1013mb or Baro is 29.92HG.
If the QNH / Baro is set to 1013mb or 29.92HG, the altitude displayed will default to the unadjusted pressure
altitude direct from the encoder. If the QNH / Baro is set to a discrete value (normally provided by ATC), the
encoder pressure altitude displayed will be adjusted for that QNH / Baro value.
The barometric units are set in the BARO option of the PROGRAM MODE. When MB is selected the QNH
screen is displayed, and when HG is selected the Baro screen is displayed.
Press MODE key (once) To select QNH / Baro option
Rotate CODE SELECT knob Scroll lower line to desired pressure.
Press ENTER key To set default value. The default is 1013(mb) or 29.92(HG
Press toggle key Display returns to current operational display
IMPORTANT NOTE
The T2000SFL will only transmit the encoder pressure altitude. The
adjusted QNH / Baro altitude is NEVER transmitted, even when it is
selected for display.
Example:
ATC provide a pressure of 1018mB, to
an aircraft flying at 5000 feet. The
difference from pressure altitude
(1013mB) is +5mB, which converts to
137 feet.
The T2000SFL will adjust the
displayed altitude by +137 feet, and
then round the value to the nearest
10Ft increment.
The Q character indicates that the
altitude value has been adjusted for
local pressure.
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