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4.2 Required Equipment Span Adjust
(See span adjust block diagram.)
1. Primary Flight Altimeter.
2. +12 or 28VDC power supply.
3. A pitot-static test set, capable of exercising the altimeter and digitizer over a range of –
1000 feet to the maximum altitude of the digitizer.
4. A ramp checker or test set capable of interrogating the transponder. Optional: ATS-400 or
equal device which will allow the display of the 100 foot resolution parallel altitude data.
4.3 Required Equipment Dynamic Calibration
(See dynamic calibration block diagram.)
1. Primary flight altimeter or NIST traceable pressure standard.
2. +12 to 28VDC power supply.
3. IBM compatible computer with an available serial port, OR Trans-Cal Industries ECP-100
Calibration/Programmer.
4. Software requirement: Windows 98®, Windows 2000® or Windows XP® using Hyper
Terminal Ver. 5.0 by Hilgraeve. (Available as a free download at http://www.hilgraeve.com) Or
equal serial data capture software. See §3.3a. (Windows Vista® is not currently supported by
Hyper Terminal.)
5. A pitot-static test set, capable of exercising the altimeter and digitizer over a range of -1000
feet to the maximum altitude of the digitizer.
6. Optional: ATS-400 or equal device which will allow the display of the 100 foot resolution
parallel altitude data.
4.4 Span Adjust Procedure
1. Connect the pitot-static test equipment to the aircraft's static line, and connect the transponder
test set per the manufacturer's recommendations. The digitizer's two altitude adjustment
potentiometers are identified as L and H, representing low and high altitude. The low
adjustment is closest to the edge of the housing, and the high adjustment is closer to the
center of the housing.
(Note: Changing either potentiometer will affect the other. An adjustment made to correct the low
transition point, will move the high transition point, and require an adjustment of the high
potentiometer.)
2. Apply power to the altitude digitizer/transponder.
3. Set the primary flight altimeter barometric pressure adjustment to 29.92 In. Hg. (1013 MB).
4. Interrogate the transponder with the ramp tester, while observing the digitizer ICAO altitude
code, decrease pressure to the point where the altitude code just makes a transition to the
maximum altitude encoded. Verify that the digitizer is within ±125 feet of the primary flight
altimeter's reading. If not, adjust the high potentiometer until the digitizer transition point is
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