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CDI Needle Deflection Deadband Problem

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comancheguytoo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote comancheguytoo Quote  Post ReplyReply Direct Link To This Post Topic: CDI Needle Deflection Deadband Problem
    Posted: 17 Jul 2015 at 2:34am
Has anyone noticed deadband or lag when turning the OBS on a CDI or HSI?  Evidently PFDs have not seen this issue.

I have a kcs-55a.  Tuning a radial or a bearing in GPS/OBS mode, the needle takes 2 degree (one dot at a time) jumps.  Effectively creating a 2-4 degree deadband on the indicator where the needle back and forths when you stop dialing.  Would make finding cross radial bearings on a check ride kind of tough.:P

Sliding my 530 back in gives the predictable smooth movement, so for the moment I'm ruling out my HSI.  The behavior in both VLOC and GPS mode rules out a VHF issue. 

OBS calibration in config mode reads smoothly in 1/10th degree increments.   Plus, the 'skips' are displayed graphically on the 540.  So the HSI must be outputting what the 540 likes.

Flying from CA to KY yesterday I tested a number of VORs, all reception was good, more or less equal to my SL30.  Also, CDI movement would continue smoothly through full deflection once the needle got out of this initial 'zone of confusion'.  

Didn't have time to practice a VOR approach, was trying to beat sunset, but here are videos of the skips:
https://drive.google.com/folderview?id=0B-y2gabArdQ-QTVZY1diYzFBSVE&usp=sharing

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AviJake View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jul 2015 at 2:46pm
This is the 2nd report of this kind of behavior.  We had an earlier report from one of our early adopters in Australia but it didn't get any traction on our end.

We'll take a look on our end.
Steve Jacobson
sjacobson@avidyne.com
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DavidBunin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DavidBunin Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2015 at 8:03pm

Jake,

I have observed similar behavior on my MD200-306 indicator.  I just figured it was the difference between digital equipment and analog equipment.

I don't have an autopilot, so any similarity between the flight plan and my actual route is mostly luck.

David

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2015 at 9:12pm
We spent a good part of Friday looking at this. No conclusions yet.
Steve Jacobson
sjacobson@avidyne.com
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rpostmo Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jul 2015 at 1:41pm
I'm driving a KCS-55a also with my IFD-540.
It acts exactly the same way in my Comanche
rpostmo
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jul 2015 at 6:49pm
Yes, it's something we're going to improve in an upcoming release.    The filtering we used in the current system results in the behavior you're all observing.   As it stands now, if you want to move 1 degree, you need to leave the knob alone for 2 seconds.  Tweaks of the course/OBS knob need 2 seconds to settle out - anything less than 2 seconds between knob adjustments will appear to have this "deadband" behavior.

Steve Jacobson
sjacobson@avidyne.com
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Post Options Post Options   Thanks (0) Thanks(0)   Quote comancheguytoo Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jul 2015 at 11:19am
Thanks Simpson.  Wanted to respond that I have found the 2 second filter delay behavior to be as you described.  

I'd add that if you tune a specific VOR radial, after the 2 sec delay you will see the needle deflect properly and then track smoothly all the way inbound or outbound.

That satisfies me that the 540 will function as needed at least in the only real world scenario where I could see myself using the NAV side vs. GPS to VOR, namely approaches.

Just don't try to get a cheat turn in while tracking VORs when your examiner is looking the other way.  ;)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jul 2015 at 11:25am
I've spent a bunch of time in the lab over the last few days looking at the improvements to this behavior and find it to be outstanding.  It will be a meaningful improvement that will be quite noticeable and will come out in the very next software release.
Steve Jacobson
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