AXP-340 Pressure Altitude Display Question

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

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!

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?

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.

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.

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

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

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.

Tom, who's doing your install, if you don't mind sharing?

Sean Andrews
Bellanca Super Viking

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.

Thanks, Tom. Much appreciated.

Sent you a PM.

Sean Andrews
Bellanca Super Viking