D180-Season variation on OAT accuracy?

[alpinelakespilot20]

I have a D180 with a "type 2" OAT probe connected via the remote magnetometer.   After moving my OAT probe to under the HS last summer, my OAT was accurate to within 1 degree F of ambient temperature when compared to two other thermometers on the ground.  That's with my correction factor on the D180 being set at "0".

However, over the past couple months, and as the temperatures have gone from about 85-90F over the summer to 20's F today,  I've noticed that my OAT is not reading nearly as accurate.  I first noticed the discrepency when my readings were becoming increasingly inconsistent with the AWOS reports .  Then to confirm it in my hangar today, I had to use the correction feature on the D180 to subtract 9F in order to get it to read the same as the two test thermometers used last summer.

(FWIW-I have checked to make sure that the D180 is looking for and using the "type 2" oat probe.  Further, my engine probes (on the cold airplane) read consistent with each other and my test thermometers.  Thus, it seems clear in my mind that it is the OAT probe that is giving an incorrect reading and not the test thermometers.)

What might account for the probe being so accurate in the summer but needing lots of correction now about 5 months later? Any help would be much appreciated.

 

[dynonsupport]

To read high, the OAT needs to go down in resistance, so it's not a loose wire. The way you "see" less resistance than expected is generally with some odd ground offset, so the best guess here would be a bad ground on your harness to the remote magnetometer, or if you have the temp probe grounded to something that is not the remote compass.

Does your OAT change with electrical load?

 

[alpinelakespilot20]

Thanks for your reply, and sorry for the delay. Holidays and life got in the way.

My OAT does not appear to change when electrical load changed.

Is there any way the probe itself (where it protrudes from the skin) could be grounding itself or does all the grounding occur somewhere in the multi-stranded shielded wire that goes from the probe to the magnetometer?

Thanks for the help.

 

[dynonsupport]

As designed (and if built correctly) there is no electrical continuity from the active elements of the the 100433-001 OAT probe with the aluminum tube of the OAT. It's conceivable that your OAT might have this happen (been built incorrectly so a component or wire in the OAT is shorting to the aluminum tube).

The ground connection for the OAT occurs in the EDC-D10A remote magnetometer via the 9-pin connector.

You can check your OAT for this condition.
1. Ensure that your FlightDEK-D180 is powered off - it provides power to the EDC-D10A.
2. Disconnect the 9-pin connector from the EDC-D10A.
3. With that connector disconnected from the EDC-D10A, check for continuity between aircraft ground, or the aluminum tube of the OAT, and Pin 8 on the 9-pin connector (see page 9-8 of the FlightDEK-D180 Installation Guide for pin numbering). There should NOT be any continuity.

Thanks for  your reply, and sorry for the delay.  Holidays and life got in the way.

My OAT does not appear to change when electrical load changed.

Is there any way the probe itself (where it protrudes from the skin) could be grounding itself or does all the grounding occur somewhere in the multi-stranded shielded wire that goes from the probe to the magnetometer?

Thanks for the help.

 

[alpinelakespilot20]

Well, it's a year later and I'm back trying to figure this problem out.  Once the weather warmed up last spring, the OAT began to read more accurately, so I kind of gave up out of desparation and for lack of necessity but again this winter it continues to read significantly low.  At about 36F the Dynon reads about 11F too high.  The discrepency gets worse the colder it gets.

- Per the above instructions, I checked for no continuity between pin 8 on the oat harness to ground, and pin 8 to the probe itself.  No continuity between either.

- I rewired the OAT harness at the connector hoping there was just a loose connection.  No luck.

- I updated the firmware on the D180 and the EDC-10A while connected to each other.  They are both now using the same firmware, but no luck.

- I bought and installed a new 3-wire Dynon OAT probe hoping it was just a bad probe.  No luck.  Temperature discrepency remained the same.

HOWEVER-
I went ahead and disconnected the probe from the EDC-10A harness and instead connected blue and yellow to the GP1 pin on the EMS side of the D180 and to ground per the  manual instructions.  I simultaneously changed the menu settings to select no OAT on EFIS side and OAT on GP1 of the EMS side. The temperature now reads perfectly with no correction needed.

So my new questions:
1.  Does the above info provide any more clues about where the problem might be with the OAT coming from the EDC-10A?

2.  If I just give up on the OAT through the EDC-10A, can I go ahead and use the GP1 input as above without any loss of D180 functionality?  (For example, will I lose any ability for the D180 to calculate TAS, density altitude or winds?)  After reading and re-reading the manual I'm still a bit unclear on this.

3.  If I do use the GP1 input in lieu of the EDC-10A input, it appears as there is no place to insert a correction factor.  Is that true?  (Not a worry at the  moment because it reads dead on through the GP1 input, but just want to make sure.)

Aside from answers to these three questions, any additional suggestions greatly appreciated.

Steve

 

[Dynon]

I'm not sure if there's a component or connecting within the EDC that could be affecting the reading, but that's the direction I'd be looking. What were you using for your ground path for the OAT probe when it was hooked to the EDC? But answers to your specific connections:

1. Maybe. Per above.
2. Yes, no loss of functionality. You may need to do a DSAB configuration with the OAT settings all changed before all of the calculations that use OAT work.
3. That's correct. Fundamentally, if OAT is wrong, the probe is either not outputting reliable information, there's a connection issue somewhere, or there's something more subtle hardware thing going on (like you may have going on with your EDC.)

 

[alpinelakespilot20]

Thank you.

My ground path for the probe when using the EDC 10A was originally shared with one of the EDC to D180 wires per older Dynon schematics.  My most recent test was with the probe grounded with blue wire to its own pin on the connector per the updated Dynon schematics.  (Sorry, I don't have the PIN numbers with me, but they were, in both instances, using Dynon schematic pin call outs.)

Given that my magnetic direction is reading correctly on the D180, I'm assuming that wiring between EDC and D180 is correct. 

Thus, would it be worthwhile to try a new EDC?  (Due to cost I'm not a fan of that, but it would save me some uncomfortable rewiring I'll need to do to to use the GP port permanently.).
Alternatively, is this bench testable at Dynon?

Thanks for your help!

 

[dynonsupport]

When was your EDC made? It may be part of this TSB from 2008, which would cause exactly what you describe:

http://www.dynonavionics.com/bulletins/support_bulletin_110107.php

 

[alpinelakespilot20]

That does sound exactly like my problem. I bought somewhere in the 2007-08 vicinity. Will go to hangar and check and get back to you.
Thanks.

 

[alpinelakespilot20]

My EDC-10A has a serial number of 7322, which appears to fall well within the serial number range of the units affected by this SB.  It looks like I either need to do the modification or send it back to Dynon.  I opened it up and it does indeed have the part that is not supposed to be there. Will get out the mini wire cutters and go after it.
Will report back.

 

[alpinelakespilot20]

Made the modification to the EDC10A per the service bulletin.  Hooked it back up.  OAT now reads dead on with the probe hooked up to the EDC10A--25F on Dynon, 25F on mercury thermometer.  No correction factor needed. All's good, at least for now. 

Will try to post back in a few months when the temparatures go back up to confirm that the Dynon is continuing to read temperatures correctly through the EDC10A.

Thanks a lot for the help!

Steve

 

[Robski]

Thanks to all for the input on this thread.

My kit is quite new, but a friend's D10A / EDC10A setup may well fall within the SB's timescale and he / we are about to put an OAT into the setup.
He's just discovered the winds aloft and TAS capabilities of the setup after I fitted my D100/D120/AP74 setup.