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OAT readings erratic

Janekom

Well Known Member
Patron
I have a few questions please.

RV10 with dual Dynon Skyview and Dual ADAHRS, with two OAT sensors.

I have erratic OAT readings. Sometime it is ok and sometimes it will go down close to 0 Degrees C where I know it should read much higher. Trying to pinpoint the problem.

Will an OAT sensor installed inside a naca duct feeding the overhead ventilation, be accurate?

Secondly how will paint influence the accuracy of the OAT sensor?

The manual states that the system will automatically choose which sensor to use? Will it switch between the two sources?

Thank you.
 
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I tried all the various locations for the OAT probes - only out on the wing provided an accurate reading. Run a four #22 conductor shielded wire to connect both (the shielding is not needed, just an easy way to do it). The bay inboard of the bell crank bay works well.

Paint should not bother it, but why paint it? If you paint it a dark color I’d guess that would not be great.

Each ADHARS has an OAT probe. The SkyView will use the OAT probe associated with the ADHARS you select as primary (normally the 200 one).

Carl
 
Thank you Carl.

With one of my previous builds years ago Dynon actually advised that the best place is under the HS.

I should have mentioned that it got painted when the paint shop did not mask them. So they are white now.

I had a look at my downloaded Skyview data and it seems to go to 0 degrees C or close to that quite often. I will check the wiring and maybe swop out the one in use with a spare I have.
 
... Away from the sunshine and away from the big furnace up front! Dynon offers some really sound advice for placement.
 
Here is what Davtron says on OAT location:

"NOTES: THE TEMPERATURE SENSOR MOUNTING SHOULD BE IN A PLACE THAT IS FREE OF EXHAUST GASES OR COWL FLAPS AIRFLOW. THE IDEAL PLACE IS TWO FEET OUT FROM THE WING ROOT ON THE BOTTOM OF THE WING. SENSOR LEADS MAY BE LENGTHENED OR SHORTENED WITHOUT AFFECTING
CALIBRATION."​


Here is what the Dynon SkyView manual says on OAT location:

"Sensor Location

The SV-OAT-340 is an outside air temperature sensor. In order for it work properly, it must be able to measure air temperature accurately. Avoid exposing the sensor to sources of heat that would interfere with outside air temperature readings such as:

  • Direct sunlight
  • Engine heat and exhaust
  • Aircraft interior (back side of sensor)
  • Heated air from the cabin exiting from an open window or cabin air exhaust port
  • The installation area should have space for a nut and wires on the back side of the sensor. It is acceptable to extend or reduce the wire length if necessary. Reduce the wire length by cutting out the desired length from the middle of the wires and splicing together the remaining ends.
  • If there is a backup ADAHRS in the SkyView system, it is acceptable to install a backup OAT sensor a few inches away from the primary sensor. Consider running primary and backup OAT sensor wiring together. Tape sensor wire pairs together to avoid confusion later."


FWIW, my RV-8 (IO-360-M1B) has a Dynon OAT probe on the aft fuselage under the right stab. A friend retrofitted a Davtron OAT probe (for an AV 30) for his RV-8 on the second outboard inspection panel of the left wing. We have compared OAT readings on several occasions when flying close together and they differ by 1°F at the most. I have heard anecdotally that the 'aft fuselage under the right stab' location does not work as well for RV's with larger engines (like those for the RV-10).

My RV-8:

i-bDjcKNz-M.jpg


My friend's RV-8:

i-QXRKfL7-M.jpg
 
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Exactly the same problem in my RV7, but I have a G3X. Did you find the solution?

With a failure always reading 0C it would seem to point to a failure of the sensor. The G3X uses a PT500 sensor and it will give an exact 500 ohm resistance at 0C. I am guessing that a failure in the sensor might give 500 ohms when it fails and hence the magical fact that the failure always shows 0C instead of a more random error. Poor location is more likely to give a %age difference from actual vs always showing 0C.
 
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