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1. 12:13 PM - ARINC 429 wiring practices (Charlie England)
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Subject: | ARINC 429 wiring practices |
I'm in the process of wiring my panel, which includes an old Garmin 430
(non-WAAS), an AFS AF4500S EFIS, AFS ARINC module, and AFS Pilot
autopilot. I'm using the AF3000-4000 Installation Guide, v7.4. Looking
through the AFS docs, their wiring diagrams are a bit...inconsistent... on
how to treat the ARINC and serial port data wiring.
So I did some digging in the InterWebs to find the 'proper' way to wire
ARINC 429 stuff. Two different sources say to ground the ARINC 429 shield
at source, destination, and at every 'break point' where additional
receivers are added, in daisy chain fashion. Easy enough; I can handle
that.
There are 3 ARINC data runs between the ARINC module and the 430. Should
each get its own shielded twisted pair, or would it be kosher to run 3
pairs in one shielded cable (and/or variations on that theme)?
In various places, there are both single and bi-directional serial runs
between/among the EFIS, 430, and other devices. In one case, they specify
that a ground return *isn't needed* (obviously depending on system
ground(s) between the EFIS & the 430). In most cases, they show a separate
ground return wire, *within* the shield of the cable. Now, I'd understand
that if the serial lines were 'balanced' (floating return), but all the
serial ground returns are electrically bonded to the chassis of the
AF4500S. Any noise imposed on the shield goes to exactly the same place
inside the unit as the separate ground return. Seems silly to run an extra
ground wire that's at the same potential as the shield.
Any thoughts on this from those who have either designed or done the actual
work on a/c using ARINC 429 and/or serial port technology?
Thanks,
Charlie
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