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AXP-340 Pressure Altitude Display Question

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pburger View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Topic: AXP-340 Pressure Altitude Display Question
    Posted: 18 May 2015 at 11:19am
If I have only the RS-232 output of my encoder connected to the AXP-340, will the Pressure Altitude display on the AXP-340 show the pressure altitude in 10' increments?

If the answer is yes, I would appreciate a picture if anyone has one.

(I know that it will display 100' increments with the parallel gray code input)

Thanks in advance...


Edited by pburger - 18 May 2015 at 11:19am
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roltman View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote roltman Quote  Post ReplyReply Direct Link To This Post Posted: 18 May 2015 at 12:43pm
Yes, it does show 10'. 
I don't have any photos handy showing the pressure altitude as all the photos I have show the flight timer. I'll try and snap some photos next time at the plane.


Edited by roltman - 18 May 2015 at 1:29pm
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pburger View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 18 May 2015 at 2:53pm
No need to snap photos, I just wanted a credible source, and I hereby deem you to be credible .

I'm at odds with my installer, and want to make sure I have my facts straight. 

In this case the issue is that I specifically requested a new encoder with RS-232 output to have the better resolution (10' v. 100').  I specifically requested that the RS-232 output be wired to the transponder.  I also requested that he wire the position output from the transponder to the IFD-540.

He wired both the parallel and the RS-232 serial outputs from the encoder to the transponder which, per the manual, defaults to the parallel gray code data, which is NOT what I wanted.  That is why I am seeing the 100' increments.  He also wired the RS-232 output from the encoder to the IFD-540, and I do see the 10' increments there.  I'm actually okay with going from the encoder straight to the IFD-540, but he needs to disconnect the parallel gray code lines to the transponder, so that the transponder will use the RS-232 serial altitude (which has the 10' increments). 

Now that I know that the altitude display on the transponder should be in 10' increments, I have a way to test it when he fixes it.

Thanks!


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roltman View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote roltman Quote  Post ReplyReply Direct Link To This Post Posted: 18 May 2015 at 3:42pm
No problem. 

I have the Sandia SAE 5-35 and during warm up on the ground I can watch it vary +/-10 on the transponder display.  We sent one RS-232 to the IFD540 #1 and use the crosslink to IFD #2.  The other RS-232 output we sent to the 340 and used it's "parrot" feature for the MLB100 input.  Finally we sent the grey code to my STec Alt pre-selector.



Edited by roltman - 18 May 2015 at 3:42pm
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pburger View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2015 at 10:05am
Wait a minute --  You have an MLB-100?  I didn't think they were out yet.  And why does an ADS-B IN unit need pressure altitude?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote n7ifr Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2015 at 10:42am
Doesn't the ADS-B IN need to have "OwnShip" pressure altitude from some source (ES transponder/encoder) to show accurate Relative target altitudes?

So, when will the MLB100 actually be available?  Still "early to mid May"?

Tom W.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote roltman Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2015 at 10:42am
No I don't have a MLB-100, but I'm pre-wired and waiting patiently to just drop it in the plane, connect a couple of wires and I'm good to go.

I think the pressure altitude is needed for relative traffic altitude computations.  I know when we did the install I read up on ADS-B and the various data sent/received, but I honestly can't recall right this second.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bneub111 Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2015 at 4:06pm
Why would you send the pressure altitude to the 540 in addition to the transponder? I don't have an ADS-B in or other traffic source - yet.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote n7ifr Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2015 at 8:20pm
It looks like some functions in the 540 require pressure altitude (from encoder/Air Data Computer data) to be automated: 

CAS (calibrated air speed) calculation, 
Density Altitude, 
VSR (vertical speed required) 
TOD (Time of descent), and 
Altitude Alert (on AXP340).

Tom W.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bneub111 Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2015 at 10:05pm
Thanks n7ifr, that makes sense.

One item I don't understand is why vertical speed required on the 540 needs baro input. Couldn't that be calculated with GPS altitude?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gring Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2015 at 8:47am
In 10.1.0.0 it is able to be computed using GPS altitude and position.  10.1.0.0 is the first release of significant enhancements and has a number of small ones like this that add usability to the box.

Edited by Gring - 20 May 2015 at 8:48am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2015 at 8:49am
Originally posted by bneub111 bneub111 wrote:

Thanks n7ifr, that makes sense.

One item I don't understand is why vertical speed required on the 540 needs baro input. Couldn't that be calculated with GPS altitude?

It can, and it will in 10.1.

Using baro altitude more directly correlates to your other aircraft instruments, and I suspect that is why the Entegra R9 panel did it that way, obviously it always has access to baro altitude. I understand that that section of code was just moved over into the 540.

* Orest



Edited by oskrypuch - 20 May 2015 at 8:51am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote n7ifr Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2015 at 5:30pm
Orest,

My 540 is near install completion this week (with pre-existing Aspen PFD/MFD), and since (I am told) the Arinc 429 line carries the input to 540 to accomplish both: 
   .  Hdg Bug synchronization PFD -->540
   .  ACU Baro Pressure --> 540 multiple calculations... 

If the '429' line will only carry one, I may have to choose - one vs the other.  
So, after the new Software Version 10.1 update with GPS Altitude integration, will this accomplish all of the 540 features otherwise related to the Pressure Alt, making the choice for HDG Bug the obvious way to go?  

Tom Wolf
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2015 at 6:00pm
The big question is, do you have an ASPEN ACU?  (original or ACU2)

* Orest

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Post Options Post Options   Thanks (0) Thanks(0)   Quote n7ifr Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2015 at 10:50pm
ACU(1) only.  I believe the lines from Aspen for ADC with raw data were wired to 540 without passing through the ACU (for filtering).

Tom W.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2015 at 9:08am
If 429 line is run straight to the 540, then you should have no trouble, all the data elements will be transmitted. You will have baro alt as well as the heading bug information available at the 540.

* Orest

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Post Options Post Options   Thanks (0) Thanks(0)   Quote bellanca1730a Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2015 at 11:05am
Tom, who's doing your install, if you don't mind sharing?
Sean Andrews
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddgates Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2015 at 11:27am

The problem has been the Aspen IM - it allows a 429 connection directly, UNLESS there is an ACU in the system.

Avidyne (Jared) has been working with Aspen about a workaround.  So far it hasn't happened.

David

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Royski Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2015 at 3:52pm
I just had a shop wire my AXP340 to receive altitude from my Aspen instead of the old encoder. Unfortunately on the flight home my mode C pressure altitude was way off, showing 500 feet instead of my altitude of 3000 feet.

Any idea what might cause this? After landing I changed the AXP to show pressure altitude in feet instead of flight level, but I haven't had a chance to see if it makes a difference.

I know I need to talk to the shop but if it's a simple software configuration issue I would like to save a trip.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote n7ifr Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2015 at 3:59pm
Sean,
Sorry about delayed response... Somehow I didn't get the email notification of forum action.

Had my 540/340/240/MLB install work out in KTRM.
I also note you are at KDVT.  I hangar on North Side.

Tom W.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bellanca1730a Quote  Post ReplyReply Direct Link To This Post Posted: 02 Aug 2015 at 8:25am
Thanks, Tom. Much appreciated.

Sent you a PM.
Sean Andrews
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jwjenks Quote  Post ReplyReply Direct Link To This Post Posted: 23 Oct 2015 at 10:21pm
I have the same problem as Royski.  I need to disable (off) the IFD and AXP Rs232 connection to get my 340 to send out the right altitude.  Why? 
JWJ
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