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Thermocouple Splicing

Practical Harness Construction - Club Level

Discussion and questions related to the course Practical Harness Construction - Club Level


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I am currently setting up a Motec M130 and C127 in my SxS and am currently getting my harness and sensors planned out. When extending alumel/chromel thermocouple wiring, what is the appropriate splicing method? My thoughts would be to simply use an open barrel splice with some SCL.

There's a couple of options. The first and most common is to use normal tefzel/TXL wire to extend the thermocouple as required. The issue with doing this is that the cold junction ends up being at this point which will typically be in the engine bay and hence you're actually going to end up measuring the temperature difference between the hot junction and cold junction - Let's say your engine bay is at 70 deg C in the vicinity of the cold junction, understandably that's going to have a significant effect on your accuracy.

The second option is to extend the wiring using thermocouple wire but this also needs to be terminated with special contacts. These should be available form most companies that deal with motorsport wiring supplies. Note that you'll still have a cold junction somewhere but inside the cabin it's likely to be more reasonable than in the engine bay. Many systems will allow the addition of a cold junction temperature sensor to compensate for the cold junction temp and provide an accurate thermocouple reading.