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Thermocouple wire

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bbradburry(at)allvantage.
Guest

Posted: Sat Aug 26, 2006 12:41 pm Post subject: Thermocouple wire

If I am going to buy wire to make my own "J" thermocouples, should I buy

stranded or solid wire for use in my plane?  If I buy stranded, do I

silver solder the ends together the same as with solid wire?  I am

looking at 24 AWG wire.

Does it make any difference whether you use "J" or "K" wire to the

instrument that you hook it up to?  In other words, can you hook up "J"

wire to an EGT meter and use it to read CHT, or OAT, or oil temp, or

whatever? (I understand that you can hook up "K" wire to an EGT meter

and use it to read CHT..That is not what I am asking.. I am wondering if

the meter is calibrated to the type of wire)



Thanks,

Bill Bradburry

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bob(at)bob-white.com
Guest

Posted: Sat Aug 26, 2006 5:31 pm Post subject: Thermocouple wire

On Sat, 26 Aug 2006 16:41:34 -0400

"Bill Bradburry" <bbradburry(at)allvantage.com> wrote:



 	  Quote: 	
		   

 

 If I am going to buy wire to make my own "J" thermocouples, should I buy

 stranded or solid wire for use in my plane?  If I buy stranded, do I

 silver solder the ends together the same as with solid wire?  I am

 looking at 24 AWG wire.

 Does it make any difference whether you use "J" or "K" wire to the

 instrument that you hook it up to?  In other words, can you hook up "J"

 wire to an EGT meter and use it to read CHT, or OAT, or oil temp, or

 whatever? (I understand that you can hook up "K" wire to an EGT meter

 and use it to read CHT..That is not what I am asking.. I am wondering if

 the meter is calibrated to the type of wire)

 

 Thanks,

 Bill Bradburry

 


	


Hi Bill,



You need to use the type wire the instrument is calibrated for to get

an accurate reading.  Each type of thermocouple has a characteristic

voltage vs temp.  Type K thermocouples are better for higher temps like

the EGT, and Type J is more suitable for lower temps like CHT.



You can make a useful TC junction by twisting the wires together,

silver soldering, spot welding, etc.  Although twisting the wires

together would only be suitable for temporary use, and you might not

have a very good junction but it would work.  Silver solder might not

make an ideal junction but it would be stable.  A good weld would be

best.  I've made J thermocouples by twisting the wires together and

melting the joint in an ox/acetylene flame.  I checked them in boiling

water and they were within a degree or two of the correct temperature.



The effect of having a not perfect junction is that the voltage vs temp

will be lower than a good TC, but it will be stable for that particular

TC.  In other words, with a "bad" junction temperature will read too

low.



One of the rotary engine guys, Todd Bartrim, has built Thermocouples

suitable for use as EGT probes.  His procedure is documented

at http://www.rotarywiki.org/wiki/tiki-index.php?page=EgtThermocouples 



Bob W.



-- 

http://www.bob-white.com

N93BD - Rotary Powered BD-4 (first engine start 1/7/06)

Custom Cables for your rotary installation -

http://www.roblinphoto.com/shop/

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ainut(at)hiwaay.net
Guest

Posted: Sat Aug 26, 2006 5:39 pm Post subject: Thermocouple wire

Bill, I strongly recommend you get the wire already manufactured for 

thermocouples.  Aircraft Spruce has 15 foot lengths that you can cut to 

the desired lengths for very little money.  The type of wire is critical 

to thermocouple usage.



David M.

Bill Bradburry wrote:



 	  Quote: 	
		  



If I am going to buy wire to make my own "J" thermocouples, should I buy

stranded or solid wire for use in my plane?  If I buy stranded, do I

silver solder the ends together the same as with solid wire?  I am

looking at 24 AWG wire.

Does it make any difference whether you use "J" or "K" wire to the

instrument that you hook it up to?  In other words, can you hook up "J"

wire to an EGT meter and use it to read CHT, or OAT, or oil temp, or

whatever? (I understand that you can hook up "K" wire to an EGT meter

and use it to read CHT..That is not what I am asking.. I am wondering if

the meter is calibrated to the type of wire)



Thanks,

Bill Bradburry

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Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Sat Aug 26, 2006 6:05 pm Post subject: Thermocouple wire

Bill;



Stranded vs. solid is your choice but bear in mind that stranded is more

flexible and less prone to vibration fatigue than solid, but both will

function.  Any point at which the two different wire alloys are joined forms

a thermocouple junction capable of generating a voltage and thus measuring

temperature. Twisting them together works, just not very long term reliable,

hence welding or silver solder can be used. Yes the instrument is calibrated

to the type of wire. The voltage vs. temperature curves for all the various

types of thermocouple wire (J, K, T, E, R, S, C,GB, etc) are quite different

and the instrument range and calibration must match the wire. One reason for

the multitude of types is to be able to measure temperatures through

different ranges. Thus your EGT and CHT thermocouples may well be different

types as might your OAT if you chose to use a thermocouple. Type J - Zero to

750 deg C  Type K - minus 200 to 1250 deg C  Type E - minus 200 to 900 deg C

Type T - minus 250 to 350 deg C etc.



ob McC

---

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_________________
Bob McC
Falco #908
(just starting)

harley(at)AgelessWings.co
Guest

Posted: Sun Aug 27, 2006 4:45 am Post subject: Thermocouple wire

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