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Im finally hooking up my autometer phantom EGT gauge, its probed into the 3rd runner of my exhaust manifold...anyways, a guy was telling me that the numbers wouldnt be accurate because of something about the metal it used and the reading would be off? Is this at all true???

Im using all the stuff i got with the autometer kit, it has the probe into the manifold, then 2 wires with two small holes, then the 2 other wires from the gauge have 2 small screws that screw into the other wire holes...hmm, just checking im not wasting my time.
 

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did you get the pyrometer or the egt gauge? i think both have the same sensor, but i've heard about those things melting cause they can't handle the heat. supposedly autometer sells a better sensor, but i'm not too sure on that. i'd say the best thing could be trial and error with this gauge, but you might want to wait and see if anyone else can give you any more info!
 

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The "Seebeck Effect" is the basis of a thermocouple temperature measurement system.

http://chem.ch.huji.ac.il/~eugeniik/history/seebeck.html

Your friend mentioned something about "metals" and "might be wrong" because every time you introduce another type of dissimilar metal junction point, you are introducing another seebeck voltage, and that is another source of error. You only ever want one cold junction, and to maintain high accuracy where it is of great concern, you can implement a cold junction compensation method to zero any unwanted offset effects.

Every "hot-rod" industry exhaust probe is based around a K-type thermocouple. This type uses a dissimilar metal pair of Chromel and Alumel wires. Chromel is the positive lead in yellow insulation (Nickel-Chrome alloy) and Alumel is the negative lead in red insulation (Nickel-Aluminum). IEC colours are green for + and white for -

If you need to extend the wires, you need to use the same types of metal, and the contacts holding them together should be made of the same metal as well. Omega sells DB crimps pins in all types of thermocouple alloys to allow pass-through wiring of thermocouple systems without introducing cold junctions...

just to give you some idea of what is available if you planned on doing things the way things are supposed to be done if you hoped to maintain any lab-grade accuracy...

http://www.omega.com/ppt/pptsc.asp?ref=TL_SL_BSJ&Nav=temg12
http://www.omega.com/ppt/pptsc.asp?ref=SM_SUB-D_CONN&Nav=temg12
http://www.omega.com/toc_asp/subsectionSC.asp?subsection=H07&book=Temperature


(yes, it gets expensive, so how accurate do you need it to be?)

It's all a moot point if you bring the thermocouple leads right into the sampling device with no dissimilar junctions, and the sampling device only needs a CJC scheme if you need to have better than 5% accuracy. Junctions that are dealt with properly are acceptable (i.e. the chromel thermocouple lead is directly touching a chromel link that is also in direct contact with the piece of chromel extension lead)

http://www.omega.com/temperature/tsc.html
 
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