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Additional encoder with Chelton

 
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Tim(at)MyRV10.com
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PostPosted: Sun Jan 22, 2006 8:49 pm    Post subject: Additional encoder with Chelton Reply with quote

Here's an offline reply that would give some info to the list if
people have similar questions....

Quote:
Tim,

I noticed this at first in the pictures, then on your latest write-up
for you panel. You mention “One nice piece of equipment in my panel is
the Ack A30 Mod 8 altitude encoder. I encourage people looking for an
encoder to look at that one. It allows 2 serial, and one Grey code
output, which comes in really handy if you have a GNS480 and an SL30.”

How come you are using a separate ACK_30 encoder to provide altitude to
your GNS480 and SL30? Can you not use the $25,000 Chelton with it’s
built in Air/Data computer to send serial or Grey code altitude to your
Nav devices? At least that way there would be no variances between what
you are flying and what you are reporting. Even the lowly Dynon 10A can
provided serial altitude to the GNS480 and SL30 with its single port.


The answer is that the Chelton doesn't have a "built-in" air data
computer. It uses an external air data computer which is actually
a crippled GRT EIS. If you get the GRT EIS, then that replaces
the air data computer that you'd get with the Chelton. (They'll
give you a credit for it.) The GRT will put out air data and
serial altitude to the Chelton. But, nobody really had a good answer
if the EIS would output the proper signals to the Transponder
and GNS480. I know the GRT EFIS would output the proper formats,
but that's after the EFIS processes the data. I had also been
told that in order to use the GTX330 TIS, I'd need an external
encoder. So I decided to get one that would do everything I'd
want. Besides that, the ACK is a TSO'd encoder, that I guess
I would think puts me in a slightly better "legal" situation
in regards to IFR static tests, as I basically have a system
between the ACK/GTX330/GNS480 that would be approvable in a
certified aircraft.

Quote:
The Mod 8 ACK encoder is the first ACK-30 to offer serial as well as
Grey code output, however I don’t see any benefit to multiple serial
outputs. A single serial output from one (ACK-30) should be able to
drive multiple devices. This is similar to the single Aviation output
serial port on my Garmin GNS-430 driving three sometimes four separate
devices—the GTX-327 Transponder, the EI Fuel Flow, the Garmin 195
portable and occasionally a tablet computer.

That's true that a serial output can drive multiple devices just
fine, but in the case of the GNS480, it prefers the 1200 baud
Apollo format, and the GTX330 prefers the GARMIN/TRIMBLE format
at 9600 baud. So rather than hooking them up and hoping that
I could get them both to recognize a common format, with only
2 wires I can hook them both up using their preferred methods.

And, what happens if you shut off the GNS430? Does the serial output
still go to the GTX-327 just fine and any other devices? I decided
that the ACK sending separate signals (which do read the exact same
altitude...and are within 10' of the GRT unit) would be a better
"fail safe" way to go. I can lose a transponder and my entire
chelton system, and still have altitude data on my GNS480.

Quote:

Seems a waste to spend all that money on the Chelton and then rely on a
$200 ACK-30 for your altitude reporting. I’ve never been able to get my
hands on the Chelton installation manuals to truly access its
capabilities so this is probably why I have never considered it. So what
am I missing that explains the separate encoder?

Well, in the big scheme of things, the $200 didn't have any impact on
my decisions. The alternative of trusting it all to the GRT maybe
could have worked, but there were enough barriers to that method,
the largest of which was the lack of information available, and making
it harder yet was when 3 different vendors couldn't decide among
themselves if I could do it without a separate encoder. When I saw
what the ACK would do, to me it simplifies things, and also gives some
good redundancy, so I'm happy with it. It's a cool little box, too.

Hope that answers the questions a bit. I'm sure there's even more
to the story that could be filled in, but I didn't have luck
getting any more info than that.

On the good side, with the exception of my music input jacks, any wires
that run out to the wing (except my trim, which is done) I now have a
fully wired, fully operational (as far as I can tell without turning
the engine on outside), and fully integrated panel. So next weekend
I'm planning to take it all to the airport for final assembly.
If I keep my same pace, I'll be ready for the DAR/FAA sometime
in February, with a target date of March 1.

Tim
Quote:

William Curtis
http://wcurtis.nerv10.com/


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dlm46007(at)cox.net
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PostPosted: Mon Jan 23, 2006 3:37 am    Post subject: Additional encoder with Chelton Reply with quote

The encoder requirement for the Chelton is really a choice in method of
implementation. The Chelton air data computer is a form of the GRT EIS which
outputs pressure altitude. The Chelton software (which is FAA certified for
their certified unit) uses the pressure altitude and altimeter setting to
display the indicated altitude for EFIS purposes. The problem arises when
transponders on the market require many different formats for input. For
years the standard has been the parallel input "grey code". Now many
transponders also allow serial inputs in different formats. Changing and
recertifying software for every new piece of hardware coming on the market
would be a daunting task as well as lend itself to errors (glitches)
creeping into the software. I have read the GRT EFIS list for some time and
the GRT software seems to be always in a state of flux. This flux would be
untenable for a certified unit; hence the isolation of the format conversion
for transponder input to the separate encoder. Therefore the purchase
decision comes down to a user decision whether to fly with a certified
software (more stable but less flexible) or a continual Beta version of
another EFIS software. Hope this helps.
---


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