[Vern]

As a product of old-style flying, I kept some steam gages as backups when I installed my Dynon D-100. Today I watched in amazement as I had an avionics tech with a $30,000 test set renew my 6A pitot static/xponder/altimeter/IFR Cert.

My calibrated backup steam-gage altimeter was no where as close as the Dynon! From -1,000 to 20,000' that Dynon was within a few feet of perfect and the airspeed was more accurate than my steam-gage airspeed indicator. My confidence level has hit a new high after watching the two-hour test process.

 

[KPmarc]

Same for me. My $700 United TSO'd altimeter was no where near as accurate or consistent as the D100 in the test from SL to 20,000 feet.

 

[Ironflight]

I've been extremely impressed with the EFIS altimeters I have seen tested - much better than any mechnical altimeter I've ever had.

 

[MCA]

Romance of the old days aside, digital systems are the way to go!

 

[Geoff]

Warm-up time?

As a product of old-style flying, I kept some steam gages as backups when I installed my Dynon D-100. Today I watched in amazement as I had an avionics tech with a $30,000 test set renew my 6A pitot static/xponder/altimeter/IFR Cert.

My calibrated backup steam-gage altimeter was no where as close as the Dynon! From -1,000 to 20,000' that Dynon was within a few feet of perfect and the airspeed was more accurate than my steam-gage airspeed indicator. My confidence level has hit a new high after watching the two-hour test process.

I have two electronic altimeters -- a Rocky Mountain Instruments Micro Encoder and a Dynon D-10A. I've noticed that the D-10A altitude is high by about a hundred feet when I first turn it on and set it to the same altimiter setting as the Micro Encoder. After 5-10 minutes, the D-10A altitude comes down to match that of the other altimeter.

Has anyone else noticed this with the D-10A? It also prevents me from using the Dynon feature that remembers the altitude when you turn it off and automatically adjusts the altimeter setting for pressure changes when you turn it back on.

 

[Geico266]

I agree. Dynons seems to be rock solid, easy to use, and pretty in the panel.

 

[Rainier Lamers]

EFIS altimeters in general

Many EFIS altimeters are based on silicon diaphram sensors and many use types like the Freescale MPX4115 or a similar device from Honeywell.
They are pretty accurate out of the box and have good temperature behaviour. They are also very linear over their pressure range with maximum deviations (uncalibrated) well below 1% of reading or range typical.

It is very difficult to make a mechanical instrument to match the repeatability, robustness and long life expectancy of these sensors.

Most EFIS manufacturers will get accuracies within 30ft below 5000 ft with slightly larger errors above this and it is largely a matter of how accurate the manufactures calibration reference is.
You will find a slight spread between sensors with respect to temperature behaviour - some are spot on, others have a slight drift. Generally, if enough money is available to pay for calibration time, even residual errors can be calibrated out.

When we started out many years ago we bought an expensive pressure reference system and a mercury manometer (just in case) only to find that the sensors we where using where in fact better than the types used in the calibration reference !
Up to today our very first instrument off the line (Stratomaster Flight, serial number FA01) is still used as crosscheck reference during calibration of our current instruments (we use 2 references so we don't get caught out by a faulty reference).

When it comes to airspeed measurements, particular at very low speeds (low pressure measurement), the electronic sensor is so far ahead it's not even funny anymore. Simply no contest.

Rainier
CEO MGL Avionics

 

[Radomir]

Geoff, you're not alone..I know one more Dynon user with same behavior... I have to say, I've never heard of altimeter "warm-up" in an EFIS so to me that doesn't sound right.

 

[frankh]

Dynon rock solid

I love both my Dynon units...I love them even better when they get totally confused when I wring the airplane out and it then says...Horizon recovering..and Boink there it is fat dumb and happy.

I would never treat a mechanical gyro they way i do thee things..

Frank

 

[Geoff]

Geoff, you're not alone..I know one more Dynon user with same behavior... I have to say, I've never heard of altimeter "warm-up" in an EFIS so to me that doesn't sound right.

I haven't called Dynon about it because it really doesn't bother me too much. By the time I get out to the runway, the Dynon is right in line with the other altimeter. As a point of reference, I'm not using the internal battery and I did not connect the "keep alive" power wire.

I do know that the Dynon instructions for calibrating the compass (internal or external) specifically require a 10-15 minute warm-up time on the unit. Not sure why that is, though...

Over all I'm extremely happy with the D-10A. The only thing I don't like is that you can't display the real-time wind vector after entering the OAT manually -- you are required to have the Dynon OAT probe (and the remote compass) to get the wind vector. Since you can use some other temperature-related features by entering the OAT manually, I think you should have the option of using the wind vector too. I suggested this to Dynon, and they said they'd consider it in a future release.

 

[Kevin Horton]

I've noticed that the D-10A altitude is high by about a hundred feet when I first turn it on and set it to the same altimiter setting as the Micro Encoder. After 5-10 minutes, the D-10A altitude comes down to match that of the other altimeter.

Has anyone else noticed this with the D-10A? It also prevents me from using the Dynon feature that remembers the altitude when you turn it off and automatically adjusts the altimeter setting for pressure changes when you turn it back on.

I checked this at the hangar yesterday. The altitude displayed on the Dynon D-10A reduced by about 40 ft over 15 minutes as it warmed up. The altitude displayed on the round dial altimeter did not change. I looked at the trend of the altimeter setting in the METARs from the closest airport that reports weather, which showed that only 10% of this change could be due to the change in atmospheric pressure.

I suspect that this is simply the effect of changing calibration as the sensors come up to their normal working temperature.

I just got my altimeter back from the instrument shop where they did the biannual calibration check. They made a small adjustment to it, and now it and the Dynon match within five feet, once the Dynon has warmed up.

 

[Dynon]

For those of you that have seen some warm-up altitude changes in our EFIS products, this is somewhat normal. The sensors need to be incredibly accurate, and to do this, we need to measure the temperature of the sensor. When you first power everything up, the temperatures are changing quickly, and it's much harder to get an accurate read on the temperature. This does cause some very slight errors that dissipate over time.

Pressure sensors need to work from (about) 16PSI down to 4 PSI. This represents about -2000 to 30,000 feet. When you want 10 foot accuracy at sea level, you need to be accurate to about .005 PSI. 1% of 12 PSI is .12 PSI, or about 24 times worse than you can handle. Almost all of that 1% error comes from temperature, so we calibrate each and every sensor in our units over a wide temperature range.

If you are seeing errors that persist beyond 10-15 minutes, or if you are seeing really big (>250 feet) errors when you power it up, we'd be glad to take a look at it here and check it out. While we do expect some error, we don't expect it to be large.

 

[Geoff]

For those of you that have seen some warm-up altitude changes in our EFIS products, this is somewhat normal. The sensors need to be incredibly accurate, and to do this, we need to measure the temperature of the sensor. When you first power everything up, the temperatures are changing quickly, and it's much harder to get an accurate read on the temperature. This does cause some very slight errors that dissipate over time.

Pressure sensors need to work from (about) 16PSI down to 4 PSI. This represents about -2000 to 30,000 feet. When you want 10 foot accuracy at sea level, you need to be accurate to about .005 PSI. 1% of 12 PSI is .12 PSI, or about 24 times worse than you can handle. Almost all of that 1% error comes from temperature, so we calibrate each and every sensor in our units over a wide temperature range.

If you are seeing errors that persist beyond 10-15 minutes, or if you are seeing really big (>250 feet) errors when you power it up, we'd be glad to take a look at it here and check it out. While we do expect some error, we don't expect it to be large.

Understand all.. However, doesn't this make your "remember the altitude at shudtown and automatically adjust the baro at startup" feature somewhat useless?

For example, if I shut down the unit with the altitude at zero feet and start it up the next day after a pressure change, it will automatically adjust the baro to make the altitude read zero feet. However, after 10 minutes of warm-up, the altitude will now read minus 50-100 feet and I'll have to manually adjust the baro anyway. For this reason, I have that feature turned off...

Other than that (and the aforementioned wind vector thing), I absolutely love the product.

 

[Dynon]

The baro auto adjust was never meant to make it so you didn't need to touch the baro. What it does is get you close so you can minimize adjustments. That being said, lots of our customers have fair success with this system, and it does work in many cases. By no means do we expect that every time you turn on the unit it is off by 100 feet.

The baro auto-adjust is never going to be perfect- there are a lot of things that can make it off by 10, 50, or even 100 feet. There's no promise that the baro you landed with was accurate, which will make the new baro wrong as well. It may also be that your shutdown sequence didn't allow us to save the old altitude accurately. All we can do is try out best.

One thing we do to try and make this better is we actually adjust twice- once right at boot, and then if you don't adjust the baro before the alt bar pops up, we do it again then, since a lot of the error pops out in the first 30 seconds. One thing to make sure you are not doing is adjusting the baro right after you turn the EFIS on.