Discussion and questions related to the course EFI Wiring Fundamentals
I am designing an engine wiring harness for a customer and need to include per cylinder EGT sensor provision (4 cyl).
Previously I have only ever plugged the sensors directly into the amplifier or ECU - with this harness I'd like ideally to provide a sealed 8 way connector in the engine compartment to collect all 4 EGTs; the ECU manufacturer states that only K/N type cables and connectors should be used; I understand the thermo-couple wire is specific, but what is the significance (if any) of the EGT connector itself? Obviously OEMs do not use K/N Type connectors and I notice AEM and others supply their sensors with Deutsch connectors - is there anything to stop me from just terminating the EGT sensor wires into a normal sealed terminal / connector arrangement, Deutsch or AMP for example?
By inserting connectors made with dissimilar metals (ie, the pins are NOT the same material as the thermocouple wire), you will introduce additional TC junctions. This may be accounted for in OEM designs, but how are you going to re-calibrate your sensors (or really amplifier output)?. Now if you are just looking for cylinder-to-cylinder variation, then all sensors should experience a similar additional TC junction offset so it may not matter.
Do you realize that is is possible to get chromel and alumel (the material in type-k thermocouples) pins & sockets for DTM & milspec connectors (yes they cost 20x the price of ordinary gold terminals). This avoids the extra junction and is the correct way to do this:
That is just the information I was looking for - thank you David.
I will take a look at those specific terminals.
G'day Alex. As usual, David has summed things up pretty brilliantly :-).
The way I think of it is that if the thermocouple wiring has a connection in it which is not made of the thermocouple material (i.e: copper), any temperature difference over this connection will not be measured. Thermocouples can only tell you the difference in temperature between two points, not any absolute values. The amplifiers deal with this by measuring the local temperature at the point where the connection to the thermocouple material is made (the connector, or PCB solder connection), and adding the difference measurement from the thermocouple to this, giving you the temperature at the end of the thermocouple.
Thanks Zac. I am going to use the terminals David linked to with an 8 way DTM connector in the engine compartment.
Just need to find a supplier in the UK, will try Rayfast tomorrow.
Thanks again guys, much appreciated