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OAT Quit Working

bob1393

Active Member
We have a little over 150 hours on our RV12, and the OAT has worked flawlessly up to now. It just stopped working cold turkey.

Talking to Van's and Dynon they say we must have a loose wire. We checked and the connections are all secure. Put an ohm meter on the two wires from the OAT gauge and we had good resistance. That implies to us that the connections are solid and that the probe itself is OK.

Anyone out there ever had OAT issues that could possibly lead us in the right direction for troubleshooting this issue?

Bob
 
Below is a quote found HERE from Dynon Support.
Dynon's OAT's are a custom made part. It's a thermistor resistor between ground and the sense wire, with a 10K resistor from sense to +5V. The thermistor is 10Kohm @ 25C, with a .25% tolerance, -4.39%/C alpha @25C, and a 3892 0C/50C beta.
Measure the voltage between the 3 wires as close to the probe as possible. Using the grounded wire are a reference, one of the other two wires should have +5 volts and the sense wire voltage should be somewhere between zero and +5, or about 2.5 volts at 25 degrees C (77 F). Check for a bad connection at D-Sub connectors.
 
Did you solve your issue? What was the issue. I just had the OAT stop working after 175 hours on the plane.
 
The issue was the probe itself. We live here in the Seattle area so drove to Dynon. They gave us a new probe to try and it worked perfectly. Have about 70 hours on the new probe with no issues.

Bob
 
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Mine will drop out

and then come back intermittently. No loose connections found so fat. All of a sudden "OAT not found" displayed, then after while it will come back. Was much more frequent before I did a bunch of Dynon updates.

Wayne 120241/143WM
 
Jumpy numbers

I recently have had two flights were I noted the Density Altitude (DA) numbers racing up down associated with the OAT numbers also racing up and down. I am assuming the OAT number movement is affecting the DA numbers.

I am suspicious of the OAT connection, two wires to a mini-plug into the AHRS behind the baggage wall. At installation, 3 or so years ago now, I recall how these two small wires from the OAT were very fragile. Reminded me of the trim wires slight nature and being a little difficult to attach the pins and insert into the plug body.

This has appeared twice between a flight of normal operation so I am still watching but I doubt if it will just go away. I have experienced "jumpy numbers" with past airplanes which were associated with poor ground or "RF leak" from a radio transmission. Both of which is much like a ghost hunt. Any ideas welcome.
 
According with KAI page 31B-14 when installing the OAT probe the nylon washer is in the outside and the nut in the inside
According with the Skyview System Installation Guide (SV-OAT_340 location and installation), the washer and the nut are in the inside. Maybe the probe needs to be grounded to work properly.
Jose del Peso (120633)
 
I too wondered first about the ground. When I checked the probe at its location under the wing the washer is on this side as called out in the plans, and was solid in the hole. Then I looked at the wire route and connection call out on KAI and noted the two wires can be oriented in either location in the mini type plug. Then plugged into the aft side of the AHRS. I am going to check those two wires and their connection. I recall they were small and a little tidious to get pinned and in that mini plug at least four years ago now.
The washer on the probe makes me less concerned because it's worked well for so long.
More to come.
 
Per an earlier post this is just a thermistor or a temperature variable resistor. As such you should just be able to measure the resistance at the connector using a multimeter. It should be in the neighborhood of 10K plus or minus the temperature related adjustment. Most of these parts nominal resistance is at 25 deg C. So it should be pretty close to 10K. This should tell you if all of your connections and the OAT probe itself is OK. Now if it is intermittent then that maybe more difficult to determine.
 
I have asked the question of the position of the washer to Van?s
This is the answer:


"The OAT probe does not rely on any airframe ground to function.

Be sure the pins are properly engaged in the microfit connector (sometimes the push out when the connector is inserted into the ADAHRS unit ".

Jose del Peso (120633)
 
Ref post #12

I took off the baggage wall and did my best gumby to access the plug, with the two wires from the OAT, into the ADAHRS(the device in back that talks to the Skyview). It appeared from the beginning one of the wires had been pushed back where I could see the crimped end of the pin sticking out from the visible part of the plug. I took the plug out, pushed the wire into the plug and it appeared to reset so I could see the contact end near the end of the plug.

I re-inserted the plug into the ADAHRS and marked the wire at the back of the plug so I could inspect it at annual and be able to tell if the wire moved. I also use a tie wrap to secure the two wires to the wire of the main connection into the ADAHRS. Test flight today and all was stable again...connector pushed back, but worked for 160 hrs until the connection wasn't good enough anymore.
 
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