Gillham code: Difference between revisions

Revision as of 22:45, 16 March 2013

Revision as of 18:04, 6 July 2013

Line 6:

}}

'''Gillham code''' is a [[Digital data|digital]] [[code]] using an eleven-wire interface that is used to transmit uncorrected [[Barometer|barometric]] [[altitude]] between an encoding altimeter or analog [[air data computer]] and a [[Transponder (aviation)|transponder]]. It is a modified form of a [[Gray code]] and is sometimes referred to as a "Gray code" in avionics literature.<ref name="Code List">[http://www.airsport-corp.com/modecascii.txt List of altitudes and Gillham codes]</ref>

The code was named in memory of Ronald Lionel Gillham, the UK's representative to the IATA committee developing the specification for the second generation of Air Traffic Control System, known in the UK as "Plan Ahead", who died suddenly in March 1968. Gillham was said to have had the idea of using a modified Gray code while at a family dinner.{{Citation needed|date=December 2010}}

Line 13:

== Altitude encoder ==

[[ImageFile:ACK A-30 Altitude Encoder 2.jpg|thumb|right|A typical altitude encoder, the ACK Technologies A-30. Note the 15-way D-type connector to send the Gillham code to the transponder and the port on the top of the case that connects to the aircraft's static pressure system.]]

An altitude encoder takes the form of a small metal box containing a pressure sensor and signal conditioning electronics.<ref name="Ameriking Encoder">[http://www.ameri-king.com/altitude_encoder.html Ameriking AK-350 Altitude Encoder]</ref><ref name="ACK Encoder">[http://www.ackavionics.com/products.htm ACK A-30 Altitude Encoder]</ref> The pressure sensor is often heated, which requires a warm-up time during which height information is either unavailable or inaccurate. Older style units can have a warm-up time of up to 10 minutes; more modern units warm up in less than 2 minutes. Some of the very latest encoders incorporate unheated 'instant on' type sensors. During the warm-up of older style units the height information may gradually increase until it settles at its final value. This is not normally a problem as the power would typically be applied before the aircraft enters the runway and so it would be transmitting correct height information soon after take-off.<ref name="Shadin Manual">[http://www.shadin.com/service/manuals/OP8800TC.pdf Shadin 8800-T Altitude Encoder Operating Manual]</ref>