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  #1  
Old 04-17-2011, 05:42 AM
GTWreck GTWreck is offline
 
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Location: Locust Grove, GA
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Question G3X OAT probe and shielding

I'm wiring up the OAT probe for my G3X, and it comes with a 3 conductor shielded cable. The manual calls for the shield to be connected to the backshell at the GSU73. I had planned for a circular connector (CPC) at each wing root. This would require that I cut the OAT cable to connect it through the CPC.

How important is it that the shield have connectivity all the way back to the AHARS (GSU73)? I figure I have 3 choices:
1. Connect the shield to a pin in the CPC
2. Ground the shield at the wing root
3. Don't connect the shield to anything.

Thoughts or suggestions?

Thanks,
Aaron
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  #2  
Old 04-17-2011, 07:14 AM
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Ironflight Ironflight is offline
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Hi Aaron,

My plan is the same as your's - a CPC connector at eh wing room. I am planning on carrying the shield through a pin - I am just guessing that the shield on the OAT is probably not THAT significant, and if I am wrong, it will not make the airplane fall out of the sky - I'll just have to go in and fix that detail. But I strongly suspect that the shielded OAT wiring is overkill....

Paul
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  #3  
Old 04-17-2011, 08:22 AM
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mburch mburch is offline
 
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Since this same OAT probe is used on everything from LSAs to the Citation Ten, I believe the fact that they went overboard with shielding is due to lightning protection requirements for the big iron. On my airplane, I plan to carry the shield through the connector via a pair of pins, just as Paul described.

mcb
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Last edited by mburch : 04-17-2011 at 11:37 AM.
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  #4  
Old 04-18-2011, 10:16 AM
Avionics Systems Avionics Systems is offline
 
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I can report from experience that we have several flying with the OAT shield carrying through connectors - both CPC and D Sub and like Matt said, there is not going to be a problem.
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  #5  
Old 07-14-2016, 01:19 AM
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rdamazio rdamazio is offline
 
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Hi all.

An additional question on this - since the probes are resistive, do you see a wrong reading from the resistance added by the connectors? (I'd imagine not or just varying the wire lengths would also have some effect)

Thanks!
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  #6  
Old 07-14-2016, 07:26 AM
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Ironflight Ironflight is offline
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With more than four years of experience, I can now say that the the CPC connector has been a pain - not for the shield, but becasue of some sort of corrosion that changes the resistance and biases the OAT readings high. I've had to go in and clean this up a couple of times now - and on an RV-3, that is a HUGE pain becasue there is just no room to easily get a hand in there to disconnect the CPC. It has taken me more than an hour of fiddling each time. Likewise, getting at it from the inside is hard becasue it is under the riveted seat pan.

Next time, I'd realize that the only way I am ever going to pull the wings off is if the airplane is in a field somewhere, so I woudl just run extra wires out the root and make the connections inside the fuse. Until you mount the wings, you just don't realize how little room is availabel between the root and the fusealge (on a -3).

Paul
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  #7  
Old 07-14-2016, 08:45 AM
Mich48041 Mich48041 is offline
 
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Maybe a thin coat of grease on the connections will help. If the connection is tight enough, the grease will be forced out from between the metal to metal contact point. The grease surrounding the contact point will help prevent corrosion.
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  #8  
Old 07-14-2016, 03:37 PM
GTWreck GTWreck is offline
 
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So far, I'm just under 1.5 years and 130+ hours past my first flight. Thus far, I have not had any corrosion issues with connections in the CPC. However, the number of nights that the plane has had to live outside a hanger is small. On the other hand, I do live in one of the most humid areas of the country.

No problems either on temperature probes reading the correct values.
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  #9  
Old 07-14-2016, 03:59 PM
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Brantel Brantel is offline
 
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Dielectric grease from the auto store should help!
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  #10  
Old 07-15-2016, 10:23 AM
SportAvServ SportAvServ is offline
 
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I have used terminal strips in the fuselage just inside the side skin. Slip the wires through a grommet in the skin with a little service length. Eyelet terminals on each wire go to the strip that is glued to the floor. Label each connection by writing on the skin or label maker. When and if a wing has to come off just unscrew each wire. Could have as many as 12 connections that are relatively easy to get to with very solid connections.
Food for thought.

Rt
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