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Thermocouple cable

design4p

Active Member
Hello,

Now working on my engine auxiliaries - I have my Garmin sensor kit with the CHT and EGT sensors. Just wondering what cable should I purchase to extend the sensor wires to the Garmin GEA 24 Engine Module.

Also, what cable is recommended to extend the fuel flow transducer (3 cables) to the GEA24.

Regards John
 
From the G3X install manual:

General Installation Guidance ? To maintain measurement accuracy, thermocouple (TC) wire must be
connected directly to the inputs of the GEA 24/GSU 73. If the supplied sensor wires are not long enough
to connect directly to the GEA 24/GSU 73, then Type K TC extension wire must be used. To minimize
risk of breakage, it is recommended that a high-quality stranded (as opposed to solid) thermocouple wire
be used. One such example of appropriate wire is TT-K-22S Type K thermocouple wire from Omega
Engineering.


I tried some cheaper stuff and even though proper therocouple type K wire, it resulted in some interesting errors - as much as 20% at 210 degrees F
 
extension cable must match thermocouple type - J or K. You can tell which by the negative conductor color.

Larry
 
The Garmin thermocouple's use type "K" thermocouple wire. You can get that at Steinair, along with everything you will need to wire your plane up. Everything you need to know about the installation, and wiring specifications, of your G3X is in the installation manual you can download from the Garmin website.
 
Thermocouple wire length

This may sound naive but should the length of the EGT and CHT thermocouple cables be the same for all cylinders or does this not matter.

Regards John
 
This may sound naive but should the length of the EGT and CHT thermocouple cables be the same for all cylinders or does this not matter.

Regards John

The correct answer is: It may matter - it depends on the instrument the thermocouple is connected to. The manufacturer should be able to advise.

Basically - if the instrument has high impedance inputs it will not load the thermocouple and length does not matter. If it has low impedance inputs it will matter.

general rule of thumb: If you are using an instrument that is powered it should have active circuitry to measure the thermocouple voltage. These tend to be high impedance (but there is no guarantee as this depends on how it is done).
If your instrument is not powered (such as with typical steam gauge indicators) the tiny voltage created by the thermocouple directly drives the needle. This loads the thermocouple and now the length and type of wire matters very much - in these cases you typically need to buy matching thermocouples from the manufacturer to get stated accuracy.

Rainier
CEO MGL Avionics
 
Thermocouple Wire

This may sound naive but should the length of the EGT and CHT thermocouple cables be the same for all cylinders or does this not matter.

Regards John

Good Morning John,

Thermocouple extension wire lengths may vary between cylinders for installation convenience; there is no requirement to use the same length of thermocouple extension wire for each engine cylinder. However, for each individual thermocouple lead, the positive and negative wires should be the same length. When attaching thermocouple extension wire with splices or connectors, the connections for an individual pair of positive/negative wires should be located close together to ensure they are exposed to similar ambient temperatures.

Thanks,

Justin
 
Does anyone know what approximate length (from the firewall) for each thermocouple cable run is required? I'd like to pre-cut and run CHT and EGT wiring through my firewall before my engine (IO-360-M1B, RV-7) arrives.
 
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