EGT and CHT indication

[paul330]

I have both the CHT and EGT probe indications from one cylinder being erratic. With the engine shut down, they are both about 10F less than ambient with the other cylinders indicating correctly. When the engine is running, the CHT is showing somewhat low and slightly unstable - the EGT is all over the place (technical description).

I have reworked the connections and am pretty sure my crimps are good. Is this what I would expect if I had cross-connected the earths?

 

[Carl_Froehlich]

I have both the CHT and EGT probe indications from one cylinder being erratic.  With the engine shut down, they are both about 10F less than ambient with the other cylinders indicating correctly.  When the engine is running, the CHT is showing somewhat low and slightly unstable - the EGT is all over the place (technical description).

I have reworked the connections and am pretty sure my crimps are good.  Is this what I would expect if I had cross-connected the earths?

These connectors are notorious for causing such problems. "Rework" does not fix it, Cut off the old spade connectors on the problematic probes and replacing them with a quality AMP connector (part number 640903-1,http://www.aircraftspruce.com/catalog/elpages/pidg.php

You will find getting to bare wire on the probe leads a pain. When ready to crimp the new connector, add a piece of #20 wire to the probe lead and then crimp. After crimping trim off the #20 wire down to the connector. The extra wire helps to get a good crimp on the probe wire.

Carl

 

[jakej]

You're on the case there except the spade ( male) connector (AMP brand) is the one to use, AS&S don't have them just the female ones (probe side)

 

[mrdaud]

OK, I've posted this before, but worth doing again.  Get rid of the spade connectors!!!!  I use dedicated TC connectors made with compatible metals and easy install.  Fixed all my problems.  You can purchase the connectors from Omega at www.omega.com.  There are male and female genders and J & K type connectors, and are reusable.  They are about 1/2" wide.  Well worth the small additional cost. Trying to post picture, but seem to be having a problem.
SMPW-CC-K-M  $2.45 ea
SMPW-CC-K-F   $2.95 ea
SMPW-CC-J-M   $2.45 ea
SMPW-CC-J-F    $2.95 ea

 

[paul330]

Actually, I am using a 4 pin Molex-type connector for each EGT/CHT pair. The others are all fine. I've had to extend the wires from the EMS - that shouldn't be an issue?

 

[jakej]

OK, I've posted this before, but worth doing again.  Get rid of the spade connectors!!!!  I use dedicated TC connectors made with compatible metals and easy install.  Fixed all my problems.  You can purchase the connectors from Omega at www.omega.com.  There are male and female genders and J & K type connectors, and are reusable.  They are about 1/2" wide.  Well worth the small additional cost. Trying to post picture, but seem to be having a problem.
SMPW-CC-K-M  $2.45 ea
SMPW-CC-K-F   $2.95 ea
SMPW-CC-J-M   $2.45 ea
SMPW-CC-J-F    $2.95 ea

Whatever works for you is good . I use the amp spades without any issues after 200 hrs & 99.5% of the 36 installs I've done use the same spades too without 'issues - just saying

 

[mrdaud]

Home Depot bolts will probably work in an airplane too, but I'd rather have AN bolts. Best to go with what is design compatible, then you know there will be no issues. I can understand an argument if we are talking 100's of dollars cost difference, but for a few extra bucks...
You will never see spade connectors used in regulated industrial thermocouple applications.

 

[paul330]

Aaaah...... Just looked at the Installation Guide and answered my own question. Seems you can't just extend the leads with any old wire :

 

[mrdaud]

Paul, you are correct. Extensions require the same wire type and gauge. K Type is made with nickel/chromium - nickel/aluminum, while J Types are made with iron - constantan (nickel/copper). For your application, you can generally extend wires without affecting accuracy. When making my own thermocouple junctions for my day job, I use a special welder that welds the two wires together to form a junction. As the welder is a bit pricey, about 2 grand, you can use a high silver content silver solder to add the extensions. I don't recommend using a butt splice. There are many suppliers for extension wire, but I use Omega at www.omega.com.