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Thermocouple compatible bulkhead connector?
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jloram

Joined: 07 Nov 2009
Posts: 54
Location: United States

Posted: Wed Feb 03, 2010 4:03 pm Post subject: Thermocouple compatible bulkhead connector?

Does any one know of a source (other than Omega) for multi-pin bulkhead

connectors that are compatible with Type J & K thermocouples? I wiring the

firewall foreword...

 

thanks, -john-

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Feb 05, 2010 7:47 am Post subject: Thermocouple compatible bulkhead connector?

John: 



My advice would be to just use a grummet.  The wires on thermocouples have

to be a consistent types of metal from the couple itself to the instrument.

Finding a multi pin bulkhead fitting in the exact correct metals may be

difficult if not impossible.



If your plane is certified be sure to follow AC43 for specs on cable

supporting.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

rjquillin(at)cox.net
Guest

Posted: Fri Feb 05, 2010 8:07 am Post subject: Thermocouple compatible bulkhead connector?

At 07:47 2/5/2010, you wrote:

  	  Quote: 	
		  The wires on thermocouples have

 to be a consistent types of metal from the couple itself to the instrument. 	


 I don't believe as stated that's entirely true.



 A voltage is developed across a junction of differing metals, that's why a TC works, but...

 If a transition is made from conductor metal type A, to conductor metal type B, we'll assume some voltage +E is developed.  However, when transitioning back from conductor metal type B to conductor metal type A, voltage E is again developed, but it is now -E.  When both transitions are at the same temperature, the voltages cancel one another out and minimal if any error voltage is generated.



 We do this all the time in a thermal-vacuum chamber used for NASA satellite/spacecraft verification all the time and it's quite acceptable; assuming the transitions are at a constant or nearly so temperature.  While the instrument within the chamber is cycled from ~ +85C to ~ -100C, the transition connector remains near ambient ~ +22C.  Errors are minimal and well within acceptable limits.



 Ron Q.



 



     [quote][b]

kcarey(at)alum.mit.edu
Guest

Posted: Fri Feb 05, 2010 8:37 am Post subject: Thermocouple compatible bulkhead connector?

Have you checked with the manufacturer of the EGT/CHT system you're using? 

I have an EI UBG-16 and when I checked with EI, they didn't have a problem 

with using a standard multi-pin connector at the bulkhead.  There are 

already two pretty common looking multi-pin connectors in the harness for 

the EGT and CHT leads installed at the factory.



Kevin



---

jloram

Joined: 07 Nov 2009
Posts: 54
Location: United States

Posted: Fri Feb 05, 2010 10:50 am Post subject: Thermocouple compatible bulkhead connector?

You're quite correct Ron. Somehow I had failed to notice that I would be  creating two, opposite polarity junctions that would be "isothermal"...  

  

 Now, I just need to find a cheap source for mil spec circular connectors  (MIL-C-5015). Anybody  have a favorite source? I need a bulkhead and plug connector with 24 pins for  the thermocouples.

  

 thanks all for comments,  -john-



 [quote]         From: owner-avionics-list-server(at)matronics.com    [mailto:owner-avionics-list-server(at)matronics.com] On Behalf Of Ron    Quillin

Sent: Friday, February 05, 2010 8:07 AM

To:    avionics-list(at)matronics.com

Subject: RE: Thermocouple    compatible bulkhead connector?

   

At 07:47 2/5/2010, you wrote:

    	  Quote: 	
		  The wires on thermocouples      have

to be a consistent types of metal from the couple itself to the      instrument. 	


I don't believe as stated that's entirely    true.



A voltage is developed across a junction of differing metals,    that's why a TC works, but...

If a transition is made from conductor metal    type A, to conductor metal type B, we'll assume some voltage +E is    developed.  However, when transitioning back from conductor metal type B    to conductor metal type A, voltage E is again developed, but it is now    -E.  When both transitions are at the same temperature, the voltages    cancel one another out and minimal if any error voltage is    generated.



We do this all the time in a thermal-vacuum chamber used for    NASA satellite/spacecraft verification all the time and it's quite acceptable;    assuming the transitions are at a constant or nearly so temperature.     While the instrument within the chamber is cycled from ~ +85C to ~ -100C, the    transition connector remains near ambient ~ +22C.  Errors are minimal and    well within acceptable limits.



Ron Q.



 	  Quote: 	
		  



href="http://www.matronics.com/Navigator?Avionics-List">http://www.matronics.com/Navigator?Avionics-List

href="http://forums.matronics.com">http://forums.matronics.com

href="http://www.matronics.com/contribution">http://www.matronics.com/c

	
[b]

jloram

Joined: 07 Nov 2009
Posts: 54
Location: United States

Posted: Fri Feb 05, 2010 10:55 am Post subject: Thermocouple compatible bulkhead connector?

Turns out that such connectors do exist in several different version. You

buy the pins separately to match the thermocouple wire. Pins cost about $20

each. However, I've finally realized that it won't be necessary to use a

special connector. (see other posts on same subject).



I'm determined not to have to disconnect 24 wires for thermocouples every

time I want to pull the engine.



-john-



[quote] --

rampil

Joined: 04 May 2007
Posts: 870

Posted: Fri Feb 05, 2010 11:55 am Post subject: Re: Thermocouple compatible bulkhead connector?

Amphenol certainly makes TC compatible pins for J & K combos.

You might be able to request samples.  These pins are usually not

stocked at Digikey or Newark, etc, but that does not mean they are

not potentially available.  Check the Amphenol catalogs for your choice

in metal or plastic circular connectors.

_________________
Ira N224XS

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Feb 05, 2010 11:59 am Post subject: Thermocouple compatible bulkhead connector?

As far as i know for certification the metals have to be consistant...  If the plane is not certified that is not a requirement.  

   

Noel  

       

From: owner-avionics-list-server(at)matronics.com [mailto:owner-avionics-list-server(at)matronics.com] On Behalf Of Ron Quillin

 Sent: February 5, 2010 12:37 PM

 To: avionics-list(at)matronics.com

 Subject: RE: Thermocouple compatible bulkhead connector?  

  

  

   

At 07:47 2/5/2010, you wrote:

 

   

The wires on thermocouples have

 to be a consistent types of metal from the couple itself to the instrument.  



 I don't believe as stated that's entirely true.

 

 A voltage is developed across a junction of differing metals, that's why a TC works, but...

 If a transition is made from conductor metal type A, to conductor metal type B, we'll assume some voltage +E is developed.  However, when transitioning back from conductor metal type B to conductor metal type A, voltage E is again developed, but it is now -E.  When both transitions are at the same temperature, the voltages cancel one another out and minimal if any error voltage is generated.

 

 We do this all the time in a thermal-vacuum chamber used for NASA satellite/spacecraft verification all the time and it's quite acceptable; assuming the transitions are at a constant or nearly so temperature.  While the instrument within the chamber is cycled from ~ +85C to ~ -100C, the transition connector remains near ambient ~ +22C.  Errors are minimal and well within acceptable limits.

 

 Ron Q.

 

 

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_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

berkut13(at)berkut13.com
Guest

Posted: Fri Feb 05, 2010 1:29 pm Post subject: Thermocouple compatible bulkhead connector?

I've used the 38999 series Mil connectors (with std  gold pins) with great success for all kinds of firewall connections - including  K and J type thermos.  Flame Enterprises as a distributor for  Mil-everything.

  

 http://www.flamecorp.com/

  

 The CPC Series 2 connectors are also good, but they  are plastic - not recommended for use on the firewall.  You can get those  from all the usual suspects - Mouser, Digi-Key, Allied, etc.  I have not  used them, but they may come in a metal form factor...dunno.

  

 James Redmon

Berkut #013/Race 13

www.berkut13.com



 [quote]   ---

rampil

Joined: 04 May 2007
Posts: 870

Posted: Tue Feb 09, 2010 8:39 am Post subject: Re: Thermocouple compatible bulkhead connector?

I think someone is confused here.

The purpose for keeping the alloys the same in the path to the voltmeter 

for T/C measurement has nothing to do with certification. It has to do

with Accuracy!  If there is a point where the metal changes, it creates a

new thermocouple (usually a "cold point") These additional thermocouples

will change the net voltage at the voltmeter and thus the temperature reading.  There is almost always a cold junction at the meter itself to 

contend with.  If you have several cold junctions in the loop at different

temps and all in the same direction of metal change, your reading will

be very inaccurate.  Yes, even if the pins are gold plated!



But then, who among us ever bothered to test the accuracy of their

CHT or EGT probes?



Thus it has always been.  Knowing the reasons for certain guidelines lets

you make sensible plans

_________________
Ira N224XS

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Feb 09, 2010 2:51 pm Post subject: Thermocouple compatible bulkhead connector?

I agree with your comment on the accuracy which is why if there are

dissimilar metals in the circuit of the T/C it will never get certified.



Noel



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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

retasker(at)optonline.net
Guest

Posted: Tue Feb 09, 2010 7:27 pm Post subject: Thermocouple compatible bulkhead connector?

Sorry, but I have to speak up regarding the confusion...  While what 

seems to be the consensus is literally true, in reality it really 

doesn't make any difference.



The way a thermocouple works is by a phenomenon called the Seebeck 

effect.  This has a complicated physics description, but the net result 

is that any metallic material that is exposed to one temperature at one 

end and another at the other, will generate a small voltage across its 

length.  Each material has its own characteristic voltage per degree 

difference between ends.  A thermocouple takes advantage of the 

different voltages by pairing two different materials - one generates 

one voltage and the other generates another.  Because they are connected 

at one end (where the desired temperature measurement is to take place) 

one can measure the voltage difference at the other end.  A so called 

"cold junction" compensation is usually provided in the gauge or meter 

that displays the temperature so that the readout shows the actual 

temperature at the far end rather than the temperature difference 

between the two ends.



Ideally the same material should be used from the temperature 

measurement point to the meter that displays the reading.



Practically speaking this is not necessary and is a source of a great 

many old wives tales.



Take the example of a connector that has the two thermocouple wires on 

each end and the connector contacts between them (i.e. thermocouple wire 

from the point of interest to the connector and then thermocouple wire 

from the connector to the meter).  Yes, the different material of the 

contacts will generate a small voltage from one end to the other based 

on the temperature difference between the two ends of the connector.  

What is this temperature difference likely to be?  Probably less that 

one degree unless it is a very long connector.  Further, both sets of 

pins are the same, so the net voltage generated by the connector will be 

zero.  So the only difference on voltage at the meter will be the very 

small temperature difference between one end of the connector and the 

other.  Considering most of us are measuring CHT (several hundred 

degrees) or EGT (1200 -1600 degrees), a degree or two is irrelevant.



If one chooses to use a connector to go through the firewall and then 

use regular copper wire to connect between the firewall connector and 

the meter in the cockpit, then that would cause an error that might be 

measurable.  If the firewall is 150 degrees and the cockpit is 70 

degrees, then there will be an error of 80 degrees in the display, which 

is definitely significant for what we are measuring - if we are trying 

to tell what the exact temperature is.  However, even in this extreme 

case, the typical use of the readout is to compare the temperature of 

the cylinders to each other or the EGTs to each other.  Even though the 

displayed temperature will not be correct, if all thermocouples go 

through the same connector, they will all be affected the same and can 

still be compared properly.



So...



A connector that is added to a set of thermocouple wires run from the 

temperature measurement point to the meter has essentially no effect on 

accuracy of the measurement.  You can even add lengths of copper wire if 

the temperature difference between the two ends of the copper wire are 

at the same temperature.  Your error in this case will be only the 

difference in temperature between the two ends of the copper wire.



There are a few caveats:



All the above regarding connectors and copper wire is true if the two 

wires from the thermocouple and connector and copper are run over the 

same physical path so they are exposed to the same temperature 

differences.  If you were to use two connectors - one for each of the 

thermocouple wires - placed far apart you could get errors that mattered 

(why you would do this I have no idea).



The materials in the path of the two thermocouple wires must be 

identical (except for the thermocouple wires themselves of course) - 

that way all the other materials will generate the same voltages in each 

path so the reading will be only what the thermocouple wires generate 

over their length - whether they are one unbroken run or a run broken by 

a connector.



If you are trying to measure temperatures of a only few degrees above 

ambient, then, while the above is still true, the errors may be too much 

for your requirements.  If you are measuring CHT and EGT adding a 

connector is irrelevant to the reading.



Dick Tasker



rampil wrote:

 	  Quote: 	
		   



 I think someone is confused here.

 The purpose for keeping the alloys the same in the path to the voltmeter

 for T/C measurement has nothing to do with certification. It has to do

 with Accuracy!  If there is a point where the metal changes, it creates a

 new thermocouple (usually a "cold point") These additional thermocouples

 will change the net voltage at the voltmeter and thus the temperature reading.  There is almost always a cold junction at the meter itself to

 contend with.  If you have several cold junctions in the loop at different

 temps and all in the same direction of metal change, your reading will

 be very inaccurate.  Yes, even if the pins are gold plated!



 But then, who among us ever bothered to test the accuracy of their

 CHT or EGT probes?



 Thus it has always been.  Knowing the reasons for certain guidelines lets

 you make sensible plans



 --------

 Ira N224XS





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 85636#285636



    


	


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douglist(at)macnauchtan.c
Guest

Posted: Tue Feb 09, 2010 8:32 pm Post subject: Thermocouple compatible bulkhead connector?

At 22:12 -0500 2/9/10, Richard E. Tasker wrote, and I snipped.:



A well thought out answer that says it all. Read it,



There was a time when thermocouples in aircraft were hooked up to sensitive D'Arsonval current meters, the analog kind with a magnet, a coiled spring, and a pointer.  Those meters measured current rather than voltage and that made the length and resistance of the wires important. Re-calibration would be required if, for instance, a thermocouple was shortened during installation or repair. The solid state digital voltmeters of today have no such problems.



When reading FAA rules of engagement remember that most of them were written 50 years ago.



Richard's use of the Seebeck effect in his description is accurate but perhaps more complicated than necessary, You won't go far wrong by thinking of a junction of two metals as a tiny temperature sensitive battery with a known voltage vs temperature function that you can look up in tables. The Omega Company is really good at providing those tables.



<http://www.omega.com/toc_asp/sectionSC.asp?section=A&book=temperature>

-- 



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jloram

Joined: 07 Nov 2009
Posts: 54
Location: United States

Posted: Thu Feb 11, 2010 3:05 pm Post subject: Thermocouple compatible bulkhead connector?

Hi Ira, I agree with you in all but one detail: when I insert a connector

into a leg of a thermocouple wire I've created three junctions. One does not

generate a voltage, and the other two junctions generate equal voltages

(because they are at the same temperature) and opposite polarity (so they

cancel out).



For example: Take a piece of thermocouple wire and cut it. Crimp a brass

connector pin on one end of the cut and a brass connector socket on the

other end of the cut. Now plug the brass pin into the brass socket. The

Brass/Brass junction does not generate a voltage because it is a junction of

similar metals. However you have created two other junctions; one is

Iron/Brass and the other is Brass/Iron. These two junctions create equal

voltages (because they are at the same temperature) but the voltages are of

opposite polarity, and cancel one another out. The connector has no net

effect.



regards, -john-

[quote] --

rampil

Joined: 04 May 2007
Posts: 870

Posted: Fri Feb 12, 2010 6:53 am Post subject: Re: Thermocouple compatible bulkhead connector?

Hi All,



I agree with all the comments that follow my snip.



The real problem is not the absolute precision or accuracy of  these systems which may each in usual practice with the cheap design gauges

(though most pricey to purchase since they carry an aviation sticker), be 10% or worse.



The issue is the basic lack of understanding in many builders (this applies

to boats and cars too!) about things electric.  Simple principles of

operation are not that hard or foreign.



Understanding the most basic principles help designers from big errors, and would as a side effect, eliminate 90% of the traffic on Bob's mediated

group.

_________________
Ira N224XS

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Feb 12, 2010 7:04 am Post subject: Thermocouple compatible bulkhead connector?

Is it reasonable to believe if the connection is going through a bulkhead

that the temperatures will be different on each side of the bulkhead?



Noel



--

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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

retasker(at)optonline.net
Guest

Posted: Fri Feb 12, 2010 10:01 am Post subject: Thermocouple compatible bulkhead connector?

Probably different, but by how much?  The thermocouple wire is connected 

on each side to a connector pin, the connector pins connected to each 

other.  All metallic and relatively good thermal conductors.



How accurately do you want to measure the CHT/EGT anyway?  As Ira noted, 

the meter is probably the "weakest link" in this accuracy equation anyway.



Dick Tasker



Noel Loveys wrote:

[quote] 



 Is it reasonable to believe if the connection is going through a bulkhead

 that the temperatures will be different on each side of the bulkhead?



 Noel



 --

jloram

Joined: 07 Nov 2009
Posts: 54
Location: United States

Posted: Fri Feb 12, 2010 10:21 am Post subject: Thermocouple compatible bulkhead connector?

It is reasonable to believe that there is a temperature difference of a few

tenths of a degree. Not enough to be perceptible by any of the

instrumentation we're using.



-john-



 



[quote] --

douglist(at)macnauchtan.c
Guest

Posted: Sat Feb 20, 2010 12:15 pm Post subject: Thermocouple compatible bulkhead connector?

Postcard in this morning's snail mail:



TC Measurement and Control Inc.

PO Box 685

Hillside, IL 60192-9922

877 449 0700



Free 72 page "wallchart format" 16 x 12 inch complete reference manual for Thermocouple and Resistance Thermometry. Request a copy at <http://www.tc-inc.com>.



And it's NOT Omega. But I'm fairly sure there is danger of getting on yet another mailing list.



-- 

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vipin

Joined: 02 Dec 2010
Posts: 3

Posted: Sun Dec 05, 2010 8:04 pm Post subject: Re: Thermocouple compatible bulkhead connector?

As far as i know for certification the metals have to be consistant... If the plane is not certified that is not a requirement.

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