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  #1  
Old 01-01-2019, 10:13 PM
JDA_BTR JDA_BTR is offline
 
Join Date: Dec 2013
Location: Baton Rouge, LA
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Default Pitot Heat and GMU22, Interfere as suspected

It was a long time ago that I fretted that this would be a problem. Ran a dedicated twisted pair out to the pitot heater outboard left wing, hoping that the pitot heater would not interfere with the magnetometer. I did ground the return wire at the fuselage and not back at the main ship ground.

Nav and strobes no problem for the magnetometer. But the pitot heater causes a 220% anomaly on the G3X interference test. It is intermittent, I suppose depending on how on/off the pitot heater control is. 90 percent of the time it works all the time (watched Anchorman this week). But that other 10 percent or less of the time it is awful.

I have a Dynon heater with controller, since that is what I planned for initially; don't know if the operating characteristics of the Garmin are the same. The Dynon seems to be very on/off and not linear.

Next step will be to run a wire to the main ship ground and see if that makes much of a difference; I suppose a lot of current right at the fuselage/wing junction could make a difference; not sure.

In operation inflight what would you see on the displays when that pitot causes interference? GTN650, G5 and dual G3X; perhaps they would just default to GPS heading? An alarm every time?

Does the Garmin pitot heat controller have a different operating characteristic?

Would a straight heater without a controller have a different characteristic?
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  #2  
Old 01-01-2019, 10:55 PM
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mgomez mgomez is offline
 
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How close is the pitot tube itself to the mag? Perhaps itís the magnetic field caused by the heating element itself, rather than the wires?
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  #3  
Old 01-01-2019, 11:03 PM
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digidocs digidocs is offline
 
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Any chance that the heater controller case (or even pitot body) is also connected to ground and the electrons are flowing through the skin instead of your carefully laid ground wire?

Could test this by electrically isolating the controller case with paper or cardboard (and pitot if necessary) to see if it affects the behavior.

I'm aware of a setup with a GMU 22 and a non-regulated Garmin pitot on the same side that works okay. I believe it's also grounded at the wing root.

David
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Old 01-02-2019, 09:25 AM
Nova RV Nova RV is offline
 
Join Date: Aug 2015
Location: Leesburg, VA
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Not sure if the Dynon makes more noise than the Garmin pitot but I have a Garmin unregulated pitot in the left wing along with GMU22 as well and it passes the interference test easily. I have 14ga shielded cable run separately from the other wires and it is grounded at the firewall "forest of tabs" as is the shield.
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  #5  
Old 01-02-2019, 03:52 PM
JDA_BTR JDA_BTR is offline
 
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Location: Baton Rouge, LA
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Itís not the controller ground because itís not screwed in currently. I was going to screw it backnupnin place and run the test again. I think an unregulated pitot would have less interference as the current changes less with time so there is less induced magnetic field. It uses more current as the trade off.

Iím going to run a wire back to the tabs and see if that changes things. If no better will prob switch to an unregulated pitot.
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  #6  
Old 01-02-2019, 04:45 PM
JDA_BTR JDA_BTR is offline
 
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Yes it makes no difference if the wire is grounded at the fuse or if it is grounded back at the tabs. The dynon regulator is too much on-off with a big current surge once or twice a minute. In the surges the magnetometer is adversely affected.

Will move now to get an unregulated heated pitot. More current but less flux. Need a good flux capacitor to use the one Iíve got. Will need a new wing access panel too. Lighter though!
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  #7  
Old 01-10-2019, 08:26 PM
JDA_BTR JDA_BTR is offline
 
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Installed the gap26 heated pitot with no regulator. Same twisted pair wiring in the wing. Grounded at the wing root to the fuselage. Magnetometer does not have any problems at all when pitot is on or off as predicted. When it is actually switched from one to the other there is a brief transient of 10-12 percent and then back to normal. The sudden current change fluxes a field but steady state no problem.

So Iíd advise against a regulated pitot in the left wing. Unregulated no sweat.

So I have a used dynon regulated pitot for sale.
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