ALT-2 Operating Manual Page 9
4.7 Calibrate
Note: This menu item is for technical personnel only, and is not displayed during the normal
operation of the instrument. Please see section 4 above on how to access this menu item. Consult
your local dealer or factory before entering this menu.
Move the highlight over the “DONE” menu item and press the rotary button to return to the main
menu.
On the back of the ALT-2 you will find the calibration number that has been determined to ensure
the most accurate reading of your altimeter. This is the value that should be entered here. hould
you have access to an accurate reference you may use this function to calibrate your altimeter.
Before you do this, ensure that you have your local pressure set to coincide with a calibrated and
certified reference. Your altimeter has been calibrated by the factory to an accuracy of +/- one mB or
approximately +/- 30 ft (10m).
The ALT-2 is calibrated in degrees Celcius. The ALT-2 is calibrated at the factory using a precision
laboratory thermometer. If recalibration is required then adjust the value using the up/down keys or
the rotary control until the temperature matches the reference ambient temperature.
5 Serial RS232 Altitude Encoder output
The ALT-2 outputs a formatted serial R 232 message that can be directly interfaced to various R 232 serial input
transponders such as those from Garmin, Trimble, Magellan, Northstar and Microair. The message contains the current
pressure altitude with a fixed reference to 1013.25mB (29.92 inches mercury). All protocols use 8 databits, no parity, and
1 stop bit. The message is outputted once a second.
Protocol Baud
Rate
Message format Example
Garmin AT 1200 #AL, space, +/-, five altitude digits right
justified zero padded, T+25, checksum,
carriage return
The checksum is a simple modulo 256 sum
of the binary values of the individual
characters. The checksum is sent as two
characters in hexadecimal format
#AL +02372T+25DF[CR]
Magellan 1200 #MGL, +/-, five altitude digits right justified
zero padded, T+25, checksum, carriage
return
The checksum is a simple modulo 256 sum
of the binary values of the individual
characters. The checksum is sent as two
characters in hexadecimal format
$MGL+02372T+2513[CR]
Northstar,
Garmin
4800 ALT, space, five altitude digits right justified
zero padded, carriage return
ALT 02372[CR]
Trimble, Garmin 9600 ALT, space, five altitude digits right justified
zero padded, carriage return
ALT 02372[CR]
MGL Avionics 9600 ALT, +/-, five altitude digits right justified
zero padded ,1013.25mB (29.92”Hg)
referenced, C, +/-, five altitude digits right
ALT+02372C+02372L1013+0000XCA[CR]
