What does "allow unit to warm for 30 minutes" mean?

[CloudSurfer]

Under the Zero Pressure Airspeed Calibration, it says "Allow unit to warm for 30 minutes before adjusting." What exactly does this mean "warm" and "adjusting?" What needs to warm up? The computer? And before adjusting what, acquiring a new calibration? Am I just supposed to leave the screens on for 30 minutes, connect it to a battery tender so it doesn't drain, and then after the screens have been on for 30 minutes press the acquire button? I just don't understand why exactly the screens need to be on for 30 minutes before doing this. Can anyone clarify? It can't be talking about the pitot tube itself warming because I have no pitot heat.

 

[Rhino]

Don't have a unit handy to look at, but I'm assuming you're referring to an on screen message, because the manual doesn't say that. I've never heard of any 30 minute warm up requirement, but my memory gets worse as I age. If you're in a hangar, as you should be, it should only take a few minutes for the system to warm up. The manual calls for five minutes, but possibly more if it's a cold environment. That's because altitude readings can fluctuate somewhat when the HDX and ADAHRS are not warmed up. This does not refer to pitot heat. You actually cover the pitot and AOA ports with a cloth or sock during this test, so you wouldn't want pitot heat on. That is, unless you like melted or burnt socks on your pitot tube.

 

[CloudSurfer]

Thanks, Rhino. Here’s the message it displays if it helps.

 

[Rhino]

I suspect that's a misprint, but you could ask Dynon to confirm. It won't hurt to let it warm up for a longer period though.

 

[RVDan]

It is very possible that the pressure sensors in the ADAHRS are temperature stabilized to improve accuracy. This is done by heating the sensor to a predetermined and tightly controlled temperature. Pressure sensors typically drift with temp changes So stabilizing them at a fixed temp improves accuracy Throughout the operating range.

 

[bruceh]

I noticed this message also. The screen menu says 30 minutes, but the manual page says at least 5 minutes for warm up.

 

[IntAvTech]

It's just what RVDan describes. The sensors need to stabilize their temperature before calibrating the zero point. As Rhino said, five minutes is probably sufficient in a warm environment but, from my experience, longer is better.

 

[Dynon]

This is referring to the sensors within the ADAHRS. Once any electronics component is powered on, there are some self-heating effects.

Thanks for highlighting the discrepancy between on-screen and the manual. Longer is generally better (again, you're trying to reach a state of equilibrium where the electronics' self-heating effect and its own ability to measure its internal temperature)

And to clarify, you definitely don't want to have pitot heat on at all.

 

[LeckieBrent]

Not the Pitot Tube: As you correctly noted, the pitot tube itself doesn't need to warm up in this context, as it's not involved in the zero pressure calibration process.