Taking your Engine's Temperature

The most popular form of experimental aircraft engine temperature monitoring device is the thermocouple. This video explores how the thermocouple works and its role in monitoring CHT, EGT, and other areas that are typically monitored in a modern experimental aircraft. Wiring the thermocouple to the instrumental panel is discussed as well as the monitoring tools needed for verifying a successful installation.
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[@giampaololucatelli6039]

Thank you. Thanks for the many information you give us! But above all for the simplicity with which you can make us understand things! Thanks again!

[@hadleymanmusic]

Temperature interpolations are a safety must to me.

[@Mrsournotes]

Nice job of explaining this Jon.👍🏽👍🏽

[@CookinCasey]

I really enjoyed watching this and learning something new. Thank you.

[@abundantYOUniverse]

Great video Jon, thanks!

[@cadude145]

It took this video and 70 years to understand how a thermocouple works.

[@johnfitzpatrick2469]

G,day from Sydney Australia. Thank you for explaining the thermocouple, using dissimilar metal wires. Also the two channel voltage meter from Amazon. Q1. Will length of wires effect continuity or a voltage drop? That was a great instruction video: hands down. 🌏🇦🇺

[@HomebuiltHELP]

No, not length nor temperature along those wires will affect reading! (with a properly designed display instrument)

[@FourthWayRanch]

you can just use 20-22 ga copper stranded wire to extend the patch cable that goes to the gauge from your probe wires. thermocouple wire not used for this.

[@volkmarmaleika1623]

Thank You for the information which will help me with my VW engine build

[@johnreed5253]

Thanks Jon!..does the type K wire come in different gauges ? Appreciate the info!

[@HomebuiltHELP]

Yes, John - whatever your supplier provides. Also comes with various outer sheaths - or no sheath whatsoever (twisted pair)

[@bibrakc]

@@HomebuiltHELP If you put different gauges for the extension will it mess up the readings?

[@commentatron]

I recently purchased a dual CHT/EGT gauge. It has two different wire pairs: Type-J (lower temp range) for the CHT, and Type-K for the EGT. Both sensor pairs have one white and one black wire (seemingly non-standard; Chinese source perhaps?). Both pairs are a typical 48" in length. The gauge also came with a 1-foot long 'extension' cable consisting of four wires: black, blue, brown and yellow with green stripe. What are these made of? Who knows. I have no idea of the composition of these extender wires, but understand it matters. As you point out, Jon, the Type-K is nickel-chromium (chromel) and alumel. The Type-J is iron wire and Constantan (copper-nickel). Aircraft Spruce and Leading Edge Airfoils both have (Westach) extension leads, but the colors don't seem to line up with any particular metal composition. What to do?

[@HomebuiltHELP]

Maybe try to verify by putting sensors in ice bath looking for 32 and boiling water looking for 212 F and see how close you are. For CHT and EGT how accurate do we really have to be? Last choice is to go to Amazon and get $30 meter and plugs to see what temps are being realized. Sometimes close enough is OK and but maybe not....

[@commentatron]

@@HomebuiltHELP Thanks Jon! I was wondering about what to use for a heat reference and boiling water is perfect.

[@commentatron]

@@HomebuiltHELP FWIW, accuracy-wise, my engine has a warmed up, ready to go temp of 120°C and a never exceed limit of 250°C (248°F and 482°F - easy to remember).

[@jpmasso]

Thank you so much!

[@dougkehoe3758]

Cool...Thanks Jon!...es?gs I noticed 5 Degreesof difference in readings ...is that because of different wire typ

[@HomebuiltHELP]

Did not see that. Where in the video was that? (time counter)

[@dougkehoe3758]

It was ts:14:58... sorry Jon, it was a .5 difference between k type reading...maybe it's nothing burger. Half of a ° shouldn't stop an install... No? I don't know 😕

[@dougkehoe3758]

Yes , good is acceptable. Was just thrown for a second when you twisted other than k type and numbers matched exact...so...when you went to the "K type"...twas a difference. FLAG!...I'm just that way, thanks again Jon Jon ,Jonny, June buggy Jon, ur the best!

[@dougkehoe3758]

Can u explain difference in temperatures of wires ? Please?

[@HomebuiltHELP]

Doug, I just reviewed the video. I see as much as .5 (half degree F) between the two sensors as I am flinging them through the air... that's pretty good accuracy I would think!

[@BC-of1ri]

Hope everything's OK. no update in 2 weeks.

[@HomebuiltHELP]

All is OK... Working on new Affordaplane videos that will eventually be posted here! Thanks for checking in.. Stay tuned!

[@ajingolk7716]

I thought a thermocouple was just a resistor/shunt which its resistance is altered by heat/temperature 😢

[@geezerguy47]

If I recall my old engineering classes right, your segment on extensions didn’t sound quite right. As I remember the law of intermediate metals state that intermediate metals have no effect provided the splices are at the same temperature. If it were not true, the connection to the instrument would be different metals as well as copper and solder on the internal circuit board. I have used plain wire extensions in the past with no change in performance.

[@HomebuiltHELP]

Thank you geezerguy for that observation. While I agree with you on the law of intermediate metals - you also did provide the reasoning for not using the wrong metals in the extension. It is often the case in our experimental aircraft engine installations that one splice of the extension is very warm (engine compartment - even close to exhaust manifolds) - and the other end of the splice may be behind the instrument panel (much cooler) While this is not always the case - using the wrong metal in the extension in this scenario would violate the law and introduce errors in temp readings. You might argue that a hand full of degrees might not make much matter when reading CHTs and EGTs - but why ask for errors when using the proper wire will maintain accuracy? As for the meter end - any good instrument has compensation built in for the metal connection. A thermocouple circuit requires a cold junction and the instrument is built to provide this function. I do have an old analog CHT gauge from years back that has a long printed warning of how to manually 'correct' readout by adding a degree for every degree above 75 - the manufacturer clearly was aware of NO built in compensation (because of the lack of electronics in their inexpensive gauge!)

[@adamli9892]

The two intermediate junctions should be at the same temperature, not that they are at the same temperature as the main junction. For example if you are using copper wires, the chromel-copper should be at the same temperature as the alumel-copper. They are usually very close because they are on the same miniature plug. They are at different temperature from the main point of chromel-alumel junction. Nice and very informative video as always. Thanks.

[@adamli9892]

I think you are right, Jon. Those intermediate temperatures need to be at the same temperature as the reference temperature which is measured in the meter.

[@HomebuiltHELP]

Hi Adam, I think it is easier to consider understanding substituting just 1 wire at a time: If you interject a single copper wire in a thermocouple K circuit, the 2 junctions at each end of the copper wire must be the same temperature in order not to affect the voltage. These two junctions of course will not be near each other and may have widely differing temperatures. Add a 2nd copper wire on the other side of the circuit and the results are similar.

[@adamli9892]

@@HomebuiltHELP You are right, Jon. The error can be eliminated if the chromel-copper/alumel-copper and the in-meter junctions are all at the same T. (Note: They do not need to be at the same T as the measuring chromel/alumel juntion). In reality, these other junctions are usually at similar T of room temperature, so that's why people use copper wire extension without big problems. But I agree with you that the alloy wires are the way to go if accurate readings are necessary.