Searching \ for '[EE] Soldering thermocouple wire?' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=soldering+thermocouple
Search entire site for: 'Soldering thermocouple wire?'.

Exact match. Not showing close matches.
PICList Thread
'[EE] Soldering thermocouple wire?'
2006\06\08@012543 by Picdude

flavicon
face
I tried to solder thermocouple wire to a PCB board, but the solder (standard 63/37, rosin-cored tin/lead solder) would not adhere to it.  Is there an easy way to solder this to a PC board?  I'd like to have the cold junction right on the PC board, but space is really tight and I cannot fit a screw terminal in there easily to join the parts

Any clues?  The thermocouple wire I have is solid, so not sure if that makes a difference, but can't see why it should.  Or are there different types of k-type thermocouple wire such that one might be easily solderable?

Thanks,
-Neil.

2006\06\08@013921 by Robert A LaBudde

flavicon
face
At 01:25 AM 6/8/2006, Neil wrote:
>I tried to solder thermocouple wire to a PCB board, but the solder
>(standard 63/37, rosin-cored tin/lead solder) would not adhere to it.  Is
>there an easy way to solder this to a PC board?  I'd like to have the cold
>junction right on the PC board, but space is really tight and I cannot fit
>a screw terminal in there easily to join the parts
>
>Any clues?  The thermocouple wire I have is solid, so not sure if that
>makes a difference, but can't see why it should.  Or are there different
>types of k-type thermocouple wire such that one might be easily solderable?

1. There is only one kind of type K wire. The whole point is
standardization of the alloys so that the junction voltage is known.

2. Type T has one wire copper and one wire constantan.

3. Try silver solder.

4. Try scuffing the surface of the wires. Type K has two ni-chrome alloys,
so the surface passivates.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: spam_OUTralTakeThisOuTspamlcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2006\06\08@020418 by Robert Rolf

picon face
You realize that any 'soldered' connection will introduce inaccuracies
in your thermocouple since you have no control over the uniformity
of the nichrome-solder-tin-copper junction. If you're not doing
trying to resolve fractions of a degree, it shouldn't be an issue,
but it sure was when we were doing that (heat flow across various
materials. delta T was less than a degree so EVERY junction had to be
identical materials right up to the cold junction. Oxidation was a
real PITA.

Dilute perchloric acid works well to solder stainless (be sure to
neutralize it immediately after use) and might work for nichrome.

http://astro.umsystem.edu/atm/ARCHIVES/JAN96/msg00108.html

"My homemade CCD camera uses thin nichrome wire to connect to the socket pins
of the very cold CCD chip.  I soldered them without difficulty by
using acid flux.  Afterward I cleaned up with Kester AP-20 flux
remover and a scrubbing in a solution of sodium bicarbonate (baking soda)
to be sure that the acid was neutralized.  No trouble after 5 years.

Also be sure to clean your soldering iron tip carefully before using
it again for electronic work.

This experience should be applicable to soldering nichrome for
anti-dew heaters.
"

Remember, google is your friend.

Robert

Robert A LaBudde wrote:

{Quote hidden}

2006\06\08@021532 by Picdude

flavicon
face


> -------- Original Message --------
> 1. There is only one kind of type K wire. The whole point is
> standardization of the alloys so that the junction voltage is known.

Correct.  This is type K.  I was wondering if strander perhaps might be easier.


> 3. Try silver solder.

I believe I have some here.  Will try it tomorrow.


> 4. Try scuffing the surface of the wires. Type K has two ni-chrome alloys,
> so the surface passivates.

Will try this as well.

Thanks,
-Neil.

2006\06\08@022528 by Picdude

flavicon
face
> -------- Original Message --------
>
> You realize that any 'soldered' connection will introduce inaccuracies
> in your thermocouple since you have no control over the uniformity
> of the nichrome-solder-tin-copper junction. If you're not doing
> trying to resolve fractions of a degree, it shouldn't be an issue,
> but it sure was when we were doing that (heat flow across various
> materials. delta T was less than a degree so EVERY junction had to be
> identical materials right up to the cold junction. Oxidation was a
> real PITA.

So you're saying that there will be many junctions within the soldered joint?  I expect this will not be a problem as the purpose of soldering the wire is to bring the cold junction right up to the temperature sensor inside the enclosure, instead of outside the enclosure.  There is one connector from the probe to the electronics enclosure (outside the enclosure), but the wires and connectors are all of the same type-K materials.


{Quote hidden}

If only I spoke it's language. :-(   This time I found lots of links regarding using thermocouples to measure the temperature of soldering irons.

I yet have to find a good electronics outlet here in South Florida so I can get these things.  Even if I order chemicals, I have to wait a week since they're not air shippable.

Cheers,
-Neil.

2006\06\08@025014 by Robert Rolf

picon face


Picdude wrote:


>>of the very cold CCD chip.  I soldered them without difficulty by
>>using acid flux.

> I yet have to find a good electronics outlet here in South Florida
so I can get these things.  Even if I order chemicals,
I have to wait a week since they're not air shippable.

Acid flux is readily available at your local plumbing/home hardware
store. Commonly use on copper pipes, particularly now that lead
solder for drinking water systems is banned in some jurisdictions.

"Plumbing" solder (non lead) may work for you, but I've never
tried it.

R


2006\06\08@031628 by Robert A LaBudde

flavicon
face
At 02:25 AM 6/8/2006, you wrote:
> > -------- Original Message --------
> >
> > You realize that any 'soldered' connection will introduce inaccuracies
> > in your thermocouple since you have no control over the uniformity
> > of the nichrome-solder-tin-copper junction. If you're not doing
> > trying to resolve fractions of a degree, it shouldn't be an issue,
> > but it sure was when we were doing that (heat flow across various
> > materials. delta T was less than a degree so EVERY junction had to be
> > identical materials right up to the cold junction. Oxidation was a
> > real PITA.
>
>So you're saying that there will be many junctions within the soldered
>joint?  I expect this will not be a problem as the purpose of soldering
>the wire is to bring the cold junction right up to the temperature sensor
>inside the enclosure, instead of outside the enclosure.  There is one
>connector from the probe to the electronics enclosure (outside the
>enclosure), but the wires and connectors are all of the same type-K materials.

All of the extra metal-metal junctions at the solder joints will be at the
cold junction temperature. The effects will therefore cancel.

Offsets due to cold junction joints are primarily due to a temperature
difference between the two wire joints. This effect will not cancel.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: .....ralKILLspamspam@spam@lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2006\06\08@032129 by Vasile Surducan

face picon face
On 6/7/06, Picdude <picdudespamKILLspamnarwani.net> wrote:
> I tried to solder thermocouple wire to a PCB board, but the solder (standard 63/37, rosin-cored tin/lead solder) would not adhere to it.  Is there an easy way to solder this to a PC board?

acid phosphoric + long wash after soldering

Vasile

I'd like to have the cold junction right on the PC board, but space is
really tight and I cannot fit a screw terminal in there easily to join
the parts
>
> Any clues?  The thermocouple wire I have is solid, so not sure if that makes a difference, but can't see why it should.  Or are there different types of k-type thermocouple wire such that one might be easily solderable?
>
> Thanks,
> -Neil.
>
> -

2006\06\08@073544 by Spehro Pefhany

picon face
At 10:25 PM 6/7/2006 -0700, you wrote:
>I tried to solder thermocouple wire to a PCB board, but the solder
>(standard 63/37, rosin-cored tin/lead solder) would not adhere to it.  Is
>there an easy way to solder this to a PC board?  I'd like to have the cold
>junction right on the PC board, but space is really tight and I cannot fit
>a screw terminal in there easily to join the parts
>
>Any clues?  The thermocouple wire I have is solid, so not sure if that
>makes a difference, but can't see why it should.  Or are there different
>types of k-type thermocouple wire such that one might be easily solderable?
>
>Thanks,
>-Neil.

If the wire is just extension wire (not the thermocouple itself), you can
substitute T wire, which has a similar EMF near ambient, without
introducing too much error for most applications.

I've also done this using SS solder and flux.

You could weld the leads to copper pins or lugs if you have a TIG welder or
spot
welder, or silver solder them. You could wet the ends of the leads with silver
solder or tin plate them, and solder that to your PCB (silver solder melts at
too high a temperature to use it directly on a PCB without damage unless
you're
using exotic materials).

Or the easiest way- use a small eg. 3.5mm terminal block.

Lots of ways to skin this particular cat.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\06\08@080428 by Gerhard Fiedler

picon face
Spehro Pefhany wrote:

> You could weld the leads to copper pins or lugs if you have a TIG welder or
> spot welder,

Or maybe crimp some copper on them?

Gerhard

2006\06\08@094115 by Spehro Pefhany

picon face
At 09:04 AM 6/8/2006 -0300, you wrote:
>Spehro Pefhany wrote:
>
> > You could weld the leads to copper pins or lugs if you have a TIG
> welder or
> > spot welder,
>
>Or maybe crimp some copper on them?
>Gerhard

Yes, I deliberately did not mention crimping. While it's possible, it requires
a very solid crimp to get a gas-tight connection, so it doesn't fail some
time later. That probably means a seamless or brazed barrel construction,
which is rare in smaller terminals, and a swaging type crimping die ($$$$).

>nnBest regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspam_OUTspamTakeThisOuTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\06\08@095410 by PicDude

flavicon
face
On Thursday 08 June 2006 02:16, Robert A LaBudde wrote:
> All of the extra metal-metal junctions at the solder joints will be at the
> cold junction temperature. The effects will therefore cancel.
>
> Offsets due to cold junction joints are primarily due to a temperature
> difference between the two wire joints. This effect will not cancel.


Right.  But I also question if I add a small piece of regular copper wire at
some point on the thermocouple wire (ie: thermocouple wire A to a small piece
of copper, then back to thermocouple wire A), and NOT at the cold junction,
would those two joints cancel out?  This assumes that the A-B joint, then B-A
joint are at the same temperature.  The reason here is to see if I can use a
standard connector (made of anything other than the thermocoupe-wire type)
instead of the thermocouple-specific wire types, without any noticeable
effects.  I've been told by some thermocouple manufacturers that I should not
do this, but can't see why, other than their having a financial interest in
selling me their connectors.

Cheers,
-Neil.

2006\06\08@112849 by Alan B. Pearce

face picon face
>But I also question if I add a small piece of regular copper
>wire at some point on the thermocouple wire (ie: thermocouple
>wire A to a small piece of copper, then back to thermocouple
>wire A), and NOT at the cold junction, would those two joints
>cancel out?  This assumes that the A-B joint, then B-A joint
>are at the same temperature.  The reason here is to see if I
>can use a standard connector (made of anything other than the
>thermocoupe-wire type) instead of the thermocouple-specific wire
>types, without any noticeable effects.  I've been told by some
>thermocouple manufacturers that I should not do this, but can't
>see why, other than their having a financial interest in
>selling me their connectors.

Well, just had a browse through the new Farnell catalogue that arrived
earlier this week, and there are "thousands" of thermocouple connectors,
with almost every manufacturer listed having an "uncompensated" connector
available that has copper contacts instead of the normal ones. I would have
thought that rather than trying to solder to the wire you would connect some
copper wires to an appropriate connector and connect those to your PCB. It
should be practical to keep that whole electronics block at an even
temperature to minimise any stray potentials that affect accuracy.

The various app notes from Linear Technology, National Semiconductor, Maxim
and possibly others all deal with minimising these problems when using the
electronic cold junction compensators. I know that LT has 2 or 3 appnotes
about this. Look for ones on the LT1025 cold junction compensation chip, and
there is one on the LT1014 quad op-amp where they use a section of the
op-amp to generate the compensation instead of a separate chip.

2006\06\12@131830 by Darrell Wyatt

picon face
part 1 1233 bytes content-type:text/plain; format=flowed (decoded quoted-printable)

Neil,

Don't know if you're aware of this, but the metals in the solder will alter the signal when they come into contact with the thermocouple wires.  Not much help, I know, but I'd hate to see you put a
lot of effort into something like this and have it fail to function as intended.

D.




{Quote hidden}

>

2006\06\12@141444 by PicDude

flavicon
face
part 1 2648 bytes content-type:text/plain; (decoded quoted-printable)

Darrell,

I am expecting that the net effect would cancel itself out -- ie: to connect metal A to metal B, if we conceptualize the soldered joint as a series of smaller connections such that A joins to X, X to Y, Y to Z, then Z to A, then the whole series would cancel itself out as long as all of the smaller joints are at the same temp, and especially so if the joint is where the cold-reference temp sensor is.

But I've had difficulties soldering the thermocouple wires to the board (tried both stranded and solid wires, and tin/lead or silver solder).  Have not been able to get any other acid solder, etc here.  So I've moved to plan B -- which is to crimp the ends to regular stranded copper wire, then solder the copper wires to the board.  The copper wires would be only about 1/4" to 1//2" inch long, and the crimped connection will be draped right over the temp sesnor.

I was trying to see if I could fit a couple of those phoenix terminals (screw terminals) onto the board, but space is tight, especially since I've managed to get the whole cold-ref control circuit (cold ref compensator / converter / amp & 20V boost regulator) into a 0.9" x 0.9" pcb.

Cheers,
-Neil.


On Monday 12 June 2006 12:18, Darrell Wyatt wrote:
{Quote hidden}

> >--

2006\06\12@151750 by Robert A LaBudde

flavicon
face
At 03:15 PM 6/12/2006, PicDude wrote:
>But I've had difficulties soldering the thermocouple wires to the board
>(tried
>both stranded and solid wires, and tin/lead or silver solder).  Have not been
>able to get any other acid solder, etc here.  So I've moved to plan B --
>which is to crimp the ends to regular stranded copper wire, then solder the
>copper wires to the board.  The copper wires would be only about 1/4" to
>1//2" inch long, and the crimped connection will be draped right over the
>temp sesnor.

You can twist the wires together and then weld the joint electrically. You
could also try a propane torch.

Acid solder flux is ammonium chloride. This may be available from other
sources. Have you tried 100% silver solder?

Ideally, all of your cold junction connections should be mounted insulated
on a heat sink to keep them all at the same temperature.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: RemoveMEralspamTakeThisOuTlcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2006\06\12@162115 by Gerhard Fiedler

picon face
Robert A LaBudde wrote:

> Ideally, all of your cold junction connections should be mounted
> insulated on a heat sink to keep them all at the same temperature.

And ideally the temp sensor for the cold junction compensation is mounted
to that same heat sink.

Gerhard

2006\06\12@164750 by PicDude

flavicon
face
On Monday 12 June 2006 14:17, Robert A LaBudde wrote:
> At 03:15 PM 6/12/2006, PicDude wrote:
> >But I've had difficulties soldering the thermocouple wires to the board
> >(tried
> >both stranded and solid wires, and tin/lead or silver solder).  Have not
> > been able to get any other acid solder, etc here.  So I've moved to plan
> > B -- which is to crimp the ends to regular stranded copper wire, then
> > solder the copper wires to the board.  The copper wires would be only
> > about 1/4" to 1//2" inch long, and the crimped connection will be draped
> > right over the temp sesnor.
>
> You can twist the wires together and then weld the joint electrically. You
> could also try a propane torch.

No welder over here in FL. :-(  But I'm planning to twist together, then crimp
the joint inside a butt-splice connector.  Just looking for a small-enough
one with the heat-shrink already over it.


> Acid solder flux is ammonium chloride. This may be available from other
> sources. Have you tried 100% silver solder?

Tried Radio Shack 63/26/2 "Silver bearing solder".  Not 100% silver.  I have
not found 100% silver anywhere yet, but I saw silver epoxy at mouser and
considering it -- essentially it is conductive epoxy, so I would twist the TC
wire ends to copper wire and join with the silver epoxy.


> Ideally, all of your cold junction connections should be mounted insulated
> on a heat sink to keep them all at the same temperature.

Heatsunk together may be a problem, but the temp sensor and cold junction are
right next to each other, and sealed within a small enclosure.  I just need
to make sure that any potting compound does not get between those 2 and add
thermal insulation.

Cheers,
-Neil.

>
> ================================================================
> Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ralEraseMEspam.....lcfltd.com
> Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
> 824 Timberlake Drive                     Tel: 757-467-0954
> Virginia Beach, VA 23464-3239            Fax: 757-467-2947
>
> "Vere scire est per causas scire"
> ================================================================

2006\06\12@170732 by Spehro Pefhany

picon face
At 04:48 PM 6/12/2006 -0500, you wrote:

>Tried Radio Shack 63/26/2 "Silver bearing solder".  Not 100% silver.  I have
>not found 100% silver anywhere yet, but I saw silver epoxy at mouser and
>considering it -- essentially it is conductive epoxy, so I would twist the TC
>wire ends to copper wire and join with the silver epoxy.

"Silver solder" is a slangish term for brazing alloys. Here's a typical one;
http://www.jwharris.com/images/pdf2/SS6.pdf

As you can see the silver content is only about 6%. The MP is low
enough that a propane torch can be used.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\06\12@174336 by Rich Graziano

picon face
What will happen if you use the thermocouple welding technique?  It seems
that the thermocouple is based on the peltier effect of the dissimilar
junction between the iron constantan or chromel alumel or what ever.  If
other metals are introduced, like tin-lead, for example, the peltier
characteristics will be altered and likely not follow the normal curve. I
have never heard of anyone soldering a thermocouple but I suppose some
people might do that.  I have seen the two separate thermocouple wires
affixed to a common substrate where the errors cancel.  If soldering is a
common practice I would sure like to hear about it and know if the soldered
junction tracks the TC curve exactly.

One idea might be to go to the Omega Website and see what products they
offer for making thermocouples.



{Original Message removed}

2006\06\12@232036 by Robert A LaBudde

flavicon
face
At 05:43 PM 6/12/2006, you wrote:
>What will happen if you use the thermocouple welding technique?  It seems
>that the thermocouple is based on the peltier effect of the dissimilar
>junction between the iron constantan or chromel alumel or what ever.  If
>other metals are introduced, like tin-lead, for example, the peltier
>characteristics will be altered and likely not follow the normal curve. I
>have never heard of anyone soldering a thermocouple but I suppose some
>people might do that.  I have seen the two separate thermocouple wires
>affixed to a common substrate where the errors cancel.  If soldering is a
>common practice I would sure like to hear about it and know if the soldered
>junction tracks the TC curve exactly.

Soldering thermocouple junctions is a common practice.

Welding of thermocouple junctions is probably the most common practice, as
you don't have the problems with soldering a variety of metals together.
There are special electrical welding apparati for such a purpose available.
Omega probably sells them.

The property is called the "thermocouple effect": i.e., generating a
voltage between dissimilar metals based on temperature.

The "Peltier effect" is the reverse: i.e., generating a temperature
difference by driving a voltage through a dissimilar metal junction.

I have made practical thermocouple junctions by twisting two wires
together, peaning them flat together, and soldering them. Welding them
together can be done easily using a car battery and jumper cables: remember
type K wire is similar to nichrome resistance wire.

Don't be too concerned about other metals present at a junction. So long as
the junction is small, all extraneous thermocouple effects will cancel.
Also note that solder is heat conductive as well as electrically
conductive, so the joint is very uniform in temperature. You should be more
concerned about flexure stress points along the thermocouple wire (type K
is not too flexible), which may create measurement junctions in annoying
places.

Any two metals can be twisted together to make a thermocouple junction with
a millivolt or two of output. The most commonly available wires are iron,
nichrome and copper. Nichrome and copper is very similar to type T wire.
Iron and copper is type J.

Commercial thermocouple wire is used because of 1) known response equations
for their particular alloys, 2) high EMF output, 3) tight linearity
specifications.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: RemoveMEralEraseMEspamEraseMElcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2006\06\13@010115 by PicDude

flavicon
face
On Monday 12 June 2006 22:20, Robert A LaBudde wrote:
> ...
> The property is called the "thermocouple effect": i.e., generating a
> voltage between dissimilar metals based on temperature.

"Seebeck effect" IIRC.


> The "Peltier effect" is the reverse: i.e., generating a temperature
> difference by driving a voltage through a dissimilar metal junction.
> ...


Cheers,
-Neil.

2006\06\13@065435 by olin piclist

face picon face
Rich Graziano wrote:
> What will happen if you use the thermocouple welding technique?  It
> seems that the thermocouple is based on the peltier effect of the
> dissimilar junction between the iron constantan or chromel alumel or
> what ever.  If other metals are introduced, like tin-lead, for example,
> the peltier characteristics will be altered and likely not follow the
> normal curve.

If all these joints are at the same temperature, the wires from there to the
electronics are of the same material, and the compenstation sensor is at the
same temperature as the ends of the thermocouple wires where they are
soldered to, then it doesn't matter at all.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\06\13@065854 by olin piclist

face picon face
Robert A LaBudde wrote:
> The property is called the "thermocouple effect": i.e., generating a
> voltage between dissimilar metals based on temperature.

No, that's not how it works.  The voltage is not generated by the junction.

******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\06\13@090702 by Darrell Wyatt

picon face
part 1 2781 bytes content-type:text/plain; format=flowed (decoded quoted-printable)




>Any two metals can be twisted together to make a thermocouple junction with
>a millivolt or two of output. The most commonly available wires are iron,
>nichrome and copper. Nichrome and copper is very similar to type T wire.
>Iron and copper is type J.
>
>Commercial thermocouple wire is used because of 1) known response equations
>for their particular alloys, 2) high EMF output, 3) tight linearity
>specifications.

-------High EMF output?  When has a millivolt signal been considered high EMF?

-------Tight linearity?  Which type of thermocouple are you referring to?  I have yet to
see any type of thermocouple that was in any way linear.  They are repeatable, and consistent,
but not in any way linear by my understanding of the word.

If you solder two thermocouple wires together, you are in effect creating two additional
thermocouple junctions.  ( at least )
The junction between thermocouple metal "A" and the solder, and the junction between
thermocouple metal "B" and the solder.  Whether or not the affects are significant in your
application are for you to decide.
I have spent the last twenty years working maintenance in foundries, injection molded
plastics, and other systems with curing ovens, etc. and I have yet to see a soldered
thermocouple wire.  I've seen some pretty crazy stuff, but not that.
There are ways to weld them, as has been posted...but if it didn't matter, why do they
have different jacks and plugs for each thermocouple type?

Like I said before, the impact of the solder joints may or may not appreciably affect your
particular application.  If you want the real skinny, check out the websites of Omega, Watlow,
Tempco, etc. etc. ad nauseum.  There is a plethora of professional ( that's exclusively what they do for a living ) information readily available.  You posted a question that falls in the "witchcraft and vodoo" realm of science where everyone seems to be an expert.  Your responses will run the gamut of possibilities.  Do some research and learn - as factually as possible - what you need to know.  It will be time well spent, and you might be able to help someone else down the road with the knowledge that you have gained.

Sorry for the rant -
D.



>
>================================================================
>Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: RemoveMEralspam_OUTspamKILLspamlcfltd.com
>Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
>824 Timberlake Drive                     Tel: 757-467-0954
>Virginia Beach, VA 23464-3239            Fax: 757-467-2947
>
>"Vere scire est per causas scire"
>================================================================
>
>

2006\06\13@100913 by Spehro Pefhany

picon face


>>Any two metals can be twisted together to make a thermocouple junction with
>>a millivolt or two of output. The most commonly available wires are iron,
>>nichrome and copper. Nichrome and copper is very similar to type T wire.
>>Iron and copper is type J.

Iron and Constantan (a copper-nickel alloy) is type J. Copper and Constantan
is type T. One alloy that is like Nichrome is called *Chromel*, and it is used
in a couple other common types of T/C.

>>Commercial thermocouple wire is used because of 1) known response equations
>>for their particular alloys, 2) high EMF output, 3) tight linearity
>>specifications.
>
>-------High EMF output?  When has a millivolt signal been considered high EMF?

It's relative. The alloys are chosen to provide relatively high EMFs. Different
metals chosen for other reasons than to make thermocouples usually have
much lower EMFs..
Sometimes even T/C alloys are chosen for other reasons (eg. they are
refractory or bio-safe),
and the EMFs are not as good or as linear (or both in the case of B).


>-------Tight linearity?  Which type of thermocouple are you referring
>to?  I have yet to
>see any type of thermocouple that was in any way linear.

Compare to a thermistor or RTD over a wide range. They are quite linear.
Just not linear
enough to ignore nonlinearity in most applications, but there are no wide
range sensors
that are, just stuff like semiconductor sensors that only work very close
to room temperature,
which is where thermocouples are least likely to be used unless there are
special requirements
that make it worth the hassle.

>  They are repeatable, and consistent,
>but not in any way linear by my understanding of the word.

The output from standard alloys conforms to the published curves quite
tightly, barring
contamination (which isn't much of an issue except at very high temperatures).

>If you solder two thermocouple wires together, you are in effect creating
>two additional
>thermocouple junctions.  ( at least )
>The junction between thermocouple metal "A" and the solder, and the
>junction between
>thermocouple metal "B" and the solder.  Whether or not the affects are
>significant in your
>application are for you to decide.

The effects are nonexistent if all the stuff is isothermal.

>I have spent the last twenty years working maintenance in foundries,
>injection molded
>plastics, and other systems with curing ovens, etc. and I have yet to see
>a soldered
>thermocouple wire.

Yes, it's not often used in industry. Ordinary PbSn solder/flux systems
don't work on
most types of thermocouples and they are often used at high temperatures
where solder would be molten (NTTAWWT). If you've worked in a foundry
you've likely
seen ones that complete the junction through molten metal. Typically
sensing junctions are
inert-gas welded.

BTW, what filler metal do you think we use when we make a conventional
3/16" grounded-junction
plastics T/C by welding? ;-)

>  I've seen some pretty crazy stuff, but not that.
>There are ways to weld them, as has been posted...but if it didn't matter,
>why do they
>have different jacks and plugs for each thermocouple type?

Because jacks and plugs are often in exposed areas with air flow, elevated
temperature,
and temperature gradients.

>Like I said before, the impact of the solder joints may or may not
>appreciably affect your
>particular application.  If you want the real skinny, check out the
>websites of Omega, Watlow,
>Tempco, etc. etc. ad nauseum.  There is a plethora of professional (
>that's exclusively what they do for a living ) information readily
>available.  You posted a question that falls in the "witchcraft and vodoo"
>realm of science where everyone seems to be an expert.

It's just regular engineering. It's only witchcraft/voodoo if you don't
understand it.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffTakeThisOuTspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\06\13@112407 by Gerhard Fiedler

picon face
Spehro Pefhany wrote:

>> Tight linearity?  Which type of thermocouple are you referring to?  I
>> have yet to see any type of thermocouple that was in any way linear.
>
> Compare to a thermistor or RTD over a wide range. They are quite linear.
> Just not linear enough to ignore nonlinearity in most applications,

I think there were a number of temperature measurement devices (like
displays) around with thermocouple inputs that had not more than a cold
junction temp compensation and a linear amplifier -- seems they are linear
enough for that application :)  Not sure such devices are still around
today; probably not.

Gerhard

2006\06\13@114433 by Robert A LaBudde

flavicon
face
At 09:06 AM 6/13/2006, Darrell wrote:
>>Commercial thermocouple wire is used because of 1) known response equations
>>for their particular alloys, 2) high EMF output, 3) tight linearity
>>specifications.
>
>-------High EMF output?  When has a millivolt signal been considered high EMF?

Just picking metals randomly gives millivolt level signals. Good choices
can raise that up to 10x.

>-------Tight linearity?  Which type of thermocouple are you referring
>to?  I have yet to
>see any type of thermocouple that was in any way linear.  They are
>repeatable, and consistent,
>but not in any way linear by my understanding of the word.

You indicate you have worked in foundry applications. Nothing is linear
over a thousand degree range. However, I believe the question related to
low temperature application. Thermocouples are typically linear to +/- 1 C
over -20 C to 150 C.

>I have spent the last twenty years working maintenance in foundries,
>injection molded plastics, and other systems with curing ovens, etc. and I
>have yet to see a soldered thermocouple wire.

Obviously soldered joints won't work for applications above 300 C.

I can only suggest you actually try making such a joint experimentally,
rather than arguing against it theoretically.

Specialized connectors for thermocouple wires serve the function of
eliminating spurious junctions where you don't want them, i.e., not at the
cold junction or the measurement junction.

Unlike most measurement system, thermocouple wire degrades in use and must
eventually be replaced. This motivates field serviceable connections.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: EraseMEralspamspamspamBeGonelcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2006\06\13@125114 by Darrell Wyatt

picon face
part 1 5996 bytes content-type:text/plain; format=flowed (decoded quoted-printable)



I stand by the information provided in my last post, but want to apologize for the tone
of it.  There are statements in this post that I disagree with as well, but response would
only perpetuate and further personalize the discussion, which typically means that the thread
would go on and on and on and on, straying further and further and further from the original
post.
It was an excellent question posed, and I'm sure we're all very interested in the outcome.
Again, the OP should do their own research and reach his or her own conclusions.
Mr. Pefhany, I apologize for originally responding in such an antagonistic fashion.  I disagree with
you, and that's okay.  That doesn't make you my enemy....At least that's what my therapissed
wants me to think....
D.



{Quote hidden}

>

2006\06\13@133226 by Spehro Pefhany

picon face
At 12:21 PM 6/13/2006 -0300, you wrote:
>Spehro Pefhany wrote:
>
> >> Tight linearity?  Which type of thermocouple are you referring to?  I
> >> have yet to see any type of thermocouple that was in any way linear.
> >
> > Compare to a thermistor or RTD over a wide range. They are quite linear.
> > Just not linear enough to ignore nonlinearity in most applications,
>
>I think there were a number of temperature measurement devices (like
>displays) around with thermocouple inputs that had not more than a cold
>junction temp compensation and a linear amplifier -- seems they are linear
>enough for that application :)

Yes, you are correct. As an instrument man, I prefer to not mention that sort
of ugliness. ;-)  You can get down to < 2% system accuracy
over a fairly wide range by using the right T/C and fudging the calibration
to even out the error using the best straight-line approximation. Or by
limiting the range.

>  Not sure such devices are still around
>today; probably not.
>
>Gerhard

Untold hundreds of thousands, I'm afraid. Like most of the K T/C functions
on inexpensive multimeters. I just checked one with my Biddle calibrator
and found it off by 35°F at midscale, but just about dead 'on' at the
endpoints.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspamEraseMEinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\06\13@162303 by PicDude

flavicon
face
On Tuesday 13 June 2006 12:44, Spehro Pefhany wrote:
{Quote hidden}

I am using the AD597, which compensates somewhat for the nonlinearity of the
thermocouples.  I don't have the datasheet in front of me, but IIRC it has 4
degC error.  There is also a higher-accuracy version.  Only thing is that
requires 20V, to get to the range I need, so I had to add a boost converter
in there.

Cheers,
-Neil.

2006\06\13@171329 by Robert A LaBudde

flavicon
face
At 05:24 PM 6/13/2006, PicDude wrote:
>I am using the AD597, which compensates somewhat for the nonlinearity of the
>thermocouples.  I don't have the datasheet in front of me, but IIRC it has 4
>degC error.  There is also a higher-accuracy version.  Only thing is that
>requires 20V, to get to the range I need, so I had to add a boost converter
>in there.

Use an external, calibrated thermometer to check the output of the AD597.
Trim externally or bias in software to correct the absolute error. The
device is linear.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: @spam@ral@spam@spamspam_OUTlcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2006\06\13@194156 by Rich Graziano

picon face
Thank you all.  Yes, I know I should have said thermocouple effect in stead
of peltier.  But I did not.  Yes they are related, but the EMF produced by
the junction is a thermocouple effect.  I wish it could be my last dumb
mistake, but alas (:-o I will do it again.

I enjoy this list so much because there are a lot of experts that will keep
me in line.  :-)
Rich
{Original Message removed}

2006\06\13@195311 by olin piclist

face picon face
Rich Graziano wrote:
> Yes they are related, but the EMF
> produced by the junction is a thermocouple effect.

Once again, it's not the junction that produces the EMF.

******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\06\14@160304 by Robert A LaBudde

flavicon
face
At 07:53 PM 6/13/2006, Olin wrote:
>Rich Graziano wrote:
> > Yes they are related, but the EMF
> > produced by the junction is a thermocouple effect.
>
>Once again, it's not the junction that produces the EMF.

It's disingenuous to say it's not the junction that produces the EMF.

Of course, it takes a temperature difference between two junctions to get
an EMF. But it is also true that every other junction at a different
temperature will also contribute to the EMF. That's why it's important to
know where the junctions are, and what temperatures are being measured.

Thermocouples have the failure mode of including extraneous junctions due
to wire stress or breaks at intermediate points. So the wires have to be
maintained and discarded periodically.

It is also true that all junctions at the same temperature sum to zero EMF
between them.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: spamBeGoneralspamKILLspamlcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2006\06\14@162318 by Gerhard Fiedler

picon face
Robert A LaBudde wrote:

> At 07:53 PM 6/13/2006, Olin wrote:
>>Rich Graziano wrote:
>>> Yes they are related, but the EMF
>>> produced by the junction is a thermocouple effect.
>>
>>Once again, it's not the junction that produces the EMF.
>
> It's disingenuous to say it's not the junction that produces the EMF.

I'm not really sure what is commonly understood as "producing an EMF", but
it seems to me that every junction produces an EMF, and what we measure as
voltage is the addition of all the EMFs of all junctions between the two
points where we measure the voltage. No?

> Of course, it takes a temperature difference between two junctions to get
> an EMF.

Is that really so? Say you have a junction and a capacitor with two plates
that are of the same material as the thermowires. I'm pretty sure the
capacitor gets loaded -- no second junction necessary.

Gerhard

2006\06\14@162819 by olin piclist

face picon face
Robert A LaBudde wrote:
> It's disingenuous to say it's not the junction that produces the EMF.

A common misconception of how thermocouples work is that the junction of
dissimilar metals produces the EMF when one side is at a different
temperature than the other.  In fact, the EMF is generated due to a
temperature gradient in each wire.  Different materials produce different
EMF for the same temperature gradient.  The resulting thermocouple voltage
is the difference in EMF generated by the two materials to the same
temperature drop.  The EMF is generated in the wires themselves.  The
junction is merely a connection point.

> Thermocouples have the failure mode of including extraneous junctions
> due to wire stress or breaks at intermediate points.

It is not due to new junctions, but increasing imperfections in the crystal
structure of the materials as they are subjected to mechanical stresses.
This alters the EMF generated for the same temperature.  Roughly speaking,
the EMF is caused by electron diffusion, and lattice irregularities impede
this diffusion.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\06\14@204428 by Marcel duchamp

picon face
The best description I have run across so far on the net is this one:

       http://www.michsci.com/documents/TechNote102-B.pdf

After reading this, it can be seen that the thermocouple effect occurs
with or without junctions.

In the real world, it is very difficult to do anything with a
thermocouple without junctions.  But the junction only allows you to use
the thermocouple; it doesn't create it.

2006\06\15@020222 by Rich Graziano

picon face
This is an excellent and valuable presentation, Marcel.  It is good for
anyone who intends to use thermocouples.

{Original Message removed}

More... (looser matching)
- Last day of these posts
- In 2006 , 2007 only
- Today
- New search...