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Dynon EFIS D100 Loses Altitude When Stored Overnight


Fly Boss

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I have noticed that when I get to the field to fly, that the altitude reading in the D100 is usually 100-300 feet below sea level.  I adjust the barometer in the D100 until the altitude reads the correct 40'. I go flying and the altitude adjusts throughout the flight correctly and when I land it reads the correct 40'.  I go home.  When I come back next time, the altitude reading is back to being between 100-300 feet below sea level.  Is it normal to have to reset the barometer reading each first time I fly?

 

Danny

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I have noticed that when I get to the field to fly, that the altitude reading in the D100 is usually 100-300 feet below sea level.  I adjust the barometer in the D100 until the altitude reads the correct 40'. I go flying and the altitude adjusts throughout the flight correctly and when I land it reads the correct 40'.  I go home.  When I come back next time, the altitude reading is back to being between 100-300 feet below sea level.  Is it normal to have to reset the barometer reading each first time I fly?

 

Danny

I don't remember what they call it, but there is a feature that you can turn on that will make it go back to the same altitude that it had when you turned it off.

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Before doing anything else, are you reading the altitude after you adjust the altimeter? I'm just curious as to what adjustments you are making to make it read 40 feet. if you are not using weather observations. It's pretty easy to get a 100-300 foot swing if you are flying in the morning and returning in the evening if there is a lot of temperature and pressure swing in your area, that's only .1 to .3 inches of mercury.

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My first thought was similar to Anticept's.

 

Is what's being observed a different altimeter setting than the last one set each time you boot up? Altitude observed each day will of course change with atmospheric pressure changes since last used.

 

Is there an internal battery that might need replacing?

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They do not have an internal battery. They use flash memory to store the settings. That's why there used to be a keep alive wire for the clock, until more recent firmware had people remove it and just pull the clock from the GPS (or keep the wire if they didn't have a compatible one).

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 Is it normal to have to reset the barometer reading each first time I fly?

 

Danny

 

 

I'm with Eddie, Anticept and Tom.  The Dynon setting in question is:

 

 

The current indicated altitude is preserved across a power cycle. When powered down, the instrument saves the indicated altitude. When it is powered up again, the instrument automatically adjusts the altimeter setting by exactly enough to preserve that saved value. This is not a replacement for modifying the altimeter setting by the pilot before takeoff; it makes it very close to the correct value, minimizing the amount of adjustment needed. To turn auto-set on or off, enter the EFIS > SETUP > BARO menu and set the ADJUST AT BOOT option to ON or OFF.

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They do not have an internal battery. They use flash memory to store the settings. That's why there used to be a keep alive wire for the clock, until more recent firmware had people remove it and just pull the clock from the GPS (or keep the wire if they didn't have a compatible one).

 

Well that answers that!  :)

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I have never had my D100 change from day to day by 200-300 ft.

 

 

The D100 does have a long 6"x1" internal battery. If you remove the D100 from its mount it has a small 1" panel on the back held by two screws. I have replaced about a dozen of them and keep batteries in stock. It is not crucial for the D100 use, but is better to have it. The #2 yellow keep alive wire was for the D120 which isn't needed and can cause errors in readings.This usually happens to the D120 and not the D100.

This wire should have been disconnected many years ago. If this hasn't been done then it needs to be done. It is the #2 pin on the D120 37 pin connector and it is yellow. 

When shutting down power the voltage on the D100 should be displayed. It is usually around 15V.

 

Error reading causes.

#2 yellow wire still connected (usually a D120 problem)

backup battery failing

software issue.    update to current software or reload current software

programming processor issue in which case the instrument needs to go back to Dynon.  $250

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Before doing anything else, are you reading the altitude after you adjust the altimeter? I'm just curious as to what adjustments you are making to make it read 40 feet. if you are not using weather observations. It's pretty easy to get a 100-300 foot swing if you are flying in the morning and returning in the evening if there is a lot of temperature and pressure swing in your area, that's only .1 to .3 inches of mercury.

 

The steam gauge altimeter appropriately reads 40' in the hanger.  This occurs at the start of each day, but yesterday I saw it on a return trip in the afternoon, suggesting that it lost its setting during lunch.  On the D100, I am in the barometer adjustments and increasing or decreasing that figure while I watch the altitude change.  I do the adjustments until the altitude reads 40'.  I think the first place to look will be in the adjust at boot settings in the Dynon.  If they are already "on", then I'll look to the battery and/or the yellow wire.  The Dynons both have current software versions. Thanks all.  I'll report back what I find.

 

Danny 

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If there is no logbook entry or you have no confirmation that the #2 yellow wire was ever disconnected then I would take a look. It only takes about 15 minutes regardless if it is part of the current problem.

 

The configuration file said that ADJUST AT BOOT was already on.  I found no logbook entry that said the yellow wire had ever been disconnected.  It has been disconnected now.  Stay tuned.

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The configuration file said that ADJUST AT BOOT was already on.  I found no logbook entry that said the yellow wire had ever been disconnected.  It has been disconnected now.  Stay tuned.

 

One thing I did notice: prior to cutting the yellow wire, when I pushed in the main battery circuit breaker, the EMS would start up automatically (nothing else).  Now that the yellow wire has been cut, when I press in the main battery circuit breaker, the EMS, EFIS, and GPS all power on (even with the avionics switch off). Is this the way it should be?

 

Danny

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One thing I did notice: prior to cutting the yellow wire, when I pushed in the main battery circuit breaker, the EMS would start up automatically (nothing else). Now that the yellow wire has been cut, when I press in the main battery circuit breaker, the EMS, EFIS, and GPS all power on (even with the avionics switch off). Is this the way it should be?

 

Danny

Turn off the avionics switch ;)
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The D100 does have a long 6"x1" internal battery. If you remove the D100 from its mount it has a small 1" panel on the back held by two screws.

 

Just so everyone is clear, this is not a clock battery, it is a BACKUP battery, It is internal to the unit, acessible through a small door, but it is different from what fastedditb, mrmorden, and I are talking about (many devices bave a little button battery to power the clock). It powers the unit if main power is lost, but doesn't do anything else. That's why dynon originally had the keep alive wire, it was a small fused wire that tapped into the main aircraft battery to power the clock. Since nearly everyone has a gps, and with the problems that wire was causing, they decided to have people remove it and sync to gps clock. I suspect some programming was relying on clock readings (easy trigger event for programming), which is honestly something that should be avoided unless absolutely necessary. It creates a significant weak point that has caused many a problem in computer history many times before, such as the Y2K bug, and the upcoming unix time bug in 2038 for systems that still use 32 bit integers for time.

 

The steam gauge altimeter appropriately reads 40' in the hanger. This occurs at the start of each day, but yesterday I saw it on a return trip in the afternoon, suggesting that it lost its setting during lunch. On the D100, I am in the barometer adjustments and increasing or decreasing that figure while I watch the altitude change. I do the adjustments until the altitude reads 40'. I think the first place to look will be in the adjust at boot settings in the Dynon. If they are already "on", then I'll look to the battery and/or the yellow wire. The Dynons both have current software versions. Thanks all. I'll report back what I find.

 

Danny

 

The steam gauge changing is to be expected. If you haven't changed the altimeter setting on it, then when local atmospheric changes occur at home base, then it too will change readings. It is because atmospheric pressure is not uniform that we have the altimeter setting in the first place; it's to compensate for these variations.

 

Simply setting it to 40' in the hangar isn't enough to determine if everything is working correctly. We also need an atmospheric pressure reading from a reliable source. An official weather observation station, like an AWOS or ASOS, will work fine. We want to compare observation at departure to observation at return. If you're getting a 300 ft swing, and the weather station reports a pressure that is .3 inches different from your first reading, then everything is working normally. But, if there is no pressure change,or you set your altimeters to the pressure reading when you returned and THEN you see a 300 ft variation, then something is definately wrong and you might ask an instrument shop to do a static test to confirm before having repairs done.

 

Be cautious about ATIS because they only report hourly, unless there are significant changes warranting a special observation, so it would be best to call the tower and ask for latest observation. Same concept as above though, compare atmospheric pressure changes to altimeter changes

 

Keep in mind that there will be a tiny little variation (few feet) as a result of temperature and humidity affecting sensors, but we're not aiming to split atoms here :).

 

Also, consider blowing out the hoses. Disconnect them from the instruments (critical!!!) and blow from there. Moisture likes to collect in those lines.

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I would not think you'd want Any avionics to come on from just the main bat/gen master breakers.  It leaves you with no option for turning off the panel  except to kill power to the entire airplane.  If it's really working that way, I'd consider that something is mis-wired.

 

I don't have a D-120, but my D-100 and 496 only come on with the avionics master.

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I would not think you'd want Any avionics to come on from just the main bat/gen master breakers.  It leaves you with no option for turning off the panel  except to kill power to the entire airplane.  If it's really working that way, I'd consider that something is mis-wired.

 

I don't have a D-120, but my D-100 and 496 only come on with the avionics master.

 

Yeah, I'm not liking it either.  In fact, the radio and transponder also came on.  Seems hard to believe that everything was as it should have been before (coming on at the right times), but cutting one wire (yes it was the yellow one in pin #2) has caused all the devices to now come on prior to turning on the avionics master.

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I suspect that while you were poking around, something else broke. Put a voltmeter across the avionics switch. You should read ~0v while it is on, and bus voltage while off. Disconnect the avionics side and do this again if you are getting anything else than what I said; if the avionics are still powered on, you have something not hooked up correctly or damaged wiring and you need to get it fixed or you face expensive repair bills.

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Turn off the avionics switch ;)

 

When I read this suggestion, my first thought was how ridiculous is that suggestion. But stranger things have happened before. So I waited to visit the plane and be sure that indeed the avionics switch was off. Imagine my surprise today when I got to the plane and found the avionics switch ON. No explanation. When I turned it off everything was as it should be. So, thanks Corey for the obvious.  It worked.

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When I read this suggestion, my first thought was how ridiculous is that suggestion. But stranger things have happened before. So I waited to visit the plane and be sure that indeed the avionics switch was off. Imagine my surprise today when I got to the plane and found the avionics switch ON. No explanation. When I turned it off everything was as it should be. So, thanks Corey for the obvious. It worked.

Happens to all of us. It's a good lesson in humility :).

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