Installing EMS firewall forward interface where previous Trutrak was

[mikelupo]

My RV-10 has a TruTrak firewall mounted EDM interface for the engine sensors and thermocouples.
The EDM mounts to the firewall aft but has a firewall forward interface.
That interface uses a standard 2-1/4 punch through with a stainless steel plate with the two DB25 pin connectors integrated into the plate. (I cannot find a picture of this to clarify my post).

https://www.bendixking.com/content/dam/bendixking/en/documents/document-lists/downloads-and-manuals/8300-065-EMS-EDM-Installation-Manual.pdf

I wonder if I can build a similar interface by using a piece of SS stock plate, and mounting the db25 pin connectors there and then relaying the wires to the EMS aft of the firewall? I’d like to reuse the hole rather than merely cover it.
Is there any detriment to relaying the signals/thermocouples through an extra set of connectors? I think the signal interfaces likely won’t be affected.
My main worry is that the thermocouples will not be accurate as the resistance may be affected.

Any experiences or advice to share here?
Thanks in advance!

 

[Rhino]

Thermocouples operate in the millivolt range and DB connectors typically have less than 10 milliohms of resistance, so I doubt resistance would be a problem. There's no guarantee however, so I personally would test the concept first. Rather than using a connector with plugs on both sides of the firewall, like the EDM, I'd opt for a standard chassis mount that has a connector on one side, and is soldered on the other. Less resistance that way. If you really want connectors on both sides, you could just re-use the existing EDM connector.

 

[mikelupo]

Thank you. All I have are crimp style. Re: The existing EDM connector… that would mean adulterating the TruTrak and I intend to sell or donate it to our EAA chapter. I can order some solder type tho! I’ll give it a shot and if temps are not reflective of what I expect them to be I’ll use a firewall penetration and bring the wires home to the Dynon EMS direct.
Thank you for your input!

 

[Dynon]

The main thing with thermocouples is that you do not have a temperature change across a junction. For example, a connection at a firewall is bad, and will cause the temperatures to be inaccurate.

 

[mikelupo]

The main thing with thermocouples is that you do not have a temperature change across a junction. For example, a connection at a firewall is bad, and will cause the temperatures to be inaccurate.

Thank you. I wonder if the difference will be 10’s of degrees or 100’s. Any experiences or test data to share?

 

[Dynon]

It's complicated, and depends on various factors. There is extensive literature on how thermocouples work and how you can induce errors in them with additional junctions, etc. You're dealing with small differences in voltages that matter though, so best to stick with best practices.

 

[mikelupo]

I purchased a firewall pass through kit and am interfacing the thermocouples direct with the unadulterated kit-supplied thermocouple harness.
I made a tray for the EMS that resembles the box that was used for the Trutrack. That part is kinda cool, but you gotta have it high enough so that it does not want to lay across the rudder pedal torque tubes. I had to support it with a strap from above. Not proud of that, but gives me some reassurance that things won't rub.