EGT / CHT Wire Leads

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bd4c
Posts: 40
Joined: Mon Oct 12, 2015 9:00 pm

EGT / CHT Wire Leads

Post by bd4c »

To better manage the abundance of thick cable, I trimmed back the wire leads on all EGT and CHT sensors (and installed better and sealed connectors). After reading the below post, I wonder if this presents an issue. I can't imagine it would, but looking for guidance.

http://eaaforums.org/showthread.php?794 ... Approaches
GRT_Jeff
Posts: 720
Joined: Tue Dec 11, 2012 12:11 am

Re: EGT / CHT Wire Leads

Post by GRT_Jeff »

The EIS manual says you can trim the wires. What you don't want to do is add different types of metal junctions that could be at different temperatures between the pairs of wire.
bd4c
Posts: 40
Joined: Mon Oct 12, 2015 9:00 pm

Re: EGT / CHT Wire Leads

Post by bd4c »

I ended up getting some clarification offline. One follow up though. For the connectors (terminals) themselves, those joining two wire segments, what are the specifications for the respective connections? For instance, are standard (off the shelf) connectors acceptable, or should very specific ones be used for CHT and EGT respectively? To illustrate, I am entirely standardized on Delphi WeatherPack connectors for all connections outside the cabin. These are all copper-zinc-tin (CuSn3Zn9).
GRT_Jeff
Posts: 720
Joined: Tue Dec 11, 2012 12:11 am

Re: EGT / CHT Wire Leads

Post by GRT_Jeff »

Standard connectors are fine. As long the connections will be about the same temperature when installed, the different metals will not cause significant error. The only case where it causes a problem is if you install one connector on one side of the firewall and the other connector on the other side of the firewall due of the temperature difference.
Sal
Posts: 8
Joined: Thu Mar 14, 2013 9:56 am

Re: EGT / CHT Wire Leads

Post by Sal »

I am experiencing high EGTs it is a camit 3300 engine. The camit supplied CHT sensors have their cold connection in the cabin while the GRT supplied EGT sensors have their cold connections in the engine compartment at a much higher temp. would this be causing some sort of calibration error.
I note in the EIS manual "This function is displayed on the hourmeter page, and shows the internal temperature of the instrument. It is used
by the instrument for cold-junction compensation of the EGTs and CHTs."
GRT_Jeff
Posts: 720
Joined: Tue Dec 11, 2012 12:11 am

Re: EGT / CHT Wire Leads

Post by GRT_Jeff »

An EIS for 4-stroke engines always has the cold junction inside the EIS. Only 2-stroke models made for "Ext CJ" have external cold junctions. The internal cold junction means the 4-stroke EIS models have to use the correct type of thermocouple wire all the way from the EIS to the EGT and CHT sensors.
Sal
Posts: 8
Joined: Thu Mar 14, 2013 9:56 am

Re: EGT / CHT Wire Leads

Post by Sal »

Jeff are you saying the thermo couple wire has to run all the way back to the D sub connector on the EIS.
I was supplied with GRT EGT probes, S/S clamp style with a set of red connectors. I have used the red connectors between the thermo couple wires and the supplied GRT loom, that connection is forward of the firewall, which then goes back to the D sub connector on the EIS.
It is the same situation with the CHT except the thermo couple wire goes back through the firewall and is connected the the EIS loom closer to the D sud.
GRT_Jeff
Posts: 720
Joined: Tue Dec 11, 2012 12:11 am

Re: EGT / CHT Wire Leads

Post by GRT_Jeff »

Yes, and it would have come that way for any normal EIS model. Did your EIS come with red and yellow pairs of wires (EGT) and red and white pairs of wires (CHT) already installed in the D-sub connector? Those are thermocouple wires straight out of the EIS D-sub. The probes also have red and yellow or red and white pairs of wires going into the red connectors. If they weren't long enough you would need to use the matching type of thermocouple wire to extend them, which is why we also sell thermocouple extension wire with the same color pairs.
Sal
Posts: 8
Joined: Thu Mar 14, 2013 9:56 am

Re: EGT / CHT Wire Leads

Post by Sal »

I have checked out my wiring spread sheet and it does say that the CHT wires are red and white and the EGT wires are red and yellow. The GRT EIS loom was long enough to reach the EGT and CHT sensor wiring they are joined with the red connectors So you think my system is wired correctly and should be reading EGT correctly. Do you know of a simple method of checking if the EGT sensor is measureing correctly.
Thanks.
GRT_Jeff
Posts: 720
Joined: Tue Dec 11, 2012 12:11 am

Re: EGT / CHT Wire Leads

Post by GRT_Jeff »

Our EIS Troubleshooting Guide has some instructions on testing the probes:
https://grtavionics.com/media/Troubleshooting-Guide.pdf
If that doesn't help, then you should e-mail support@grtavionics.com directly with your EIS model info so our EIS techs can try to help.
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