Question about Thermocouple

[K Wind]

I want to build a cold compensation circuit for a type K thermocouple that I
have. The two wires are soldered together at the end. I plan on using
boiling water and ice water to calibrate. Can I put the end of the probe
into the water just the way it is?

Ken

 

[John Larkin]

On Sun, 31 Aug 2003 14:32:00 GMT, "K Wind"
<kwind@news-server.neo.rr.com> wrote:

I want to build a cold compensation circuit for a type K thermocouple that I
have. The two wires are soldered together at the end. I plan on using
boiling water and ice water to calibrate. Can I put the end of the probe
into the water just the way it is?

Ken

Sure. But make sure the cold cal is done with lots of well-crushed
ice, stirred frequently. Just some ice cubes in a glass of water can
be pretty far off. And adjust your boiling point for altitude.

John

 

[Garrett Mace]

"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:0rd4lvckleohjglnbbrgutoieo8ben47oc@4ax.com...

On Sun, 31 Aug 2003 14:32:00 GMT, "K Wind"
kwind@news-server.neo.rr.com> wrote:

I want to build a cold compensation circuit for a type K thermocouple
that I
have. The two wires are soldered together at the end. I plan on using
boiling water and ice water to calibrate. Can I put the end of the probe
into the water just the way it is?

Ken


Sure. But make sure the cold cal is done with lots of well-crushed
ice, stirred frequently. Just some ice cubes in a glass of water can
be pretty far off. And adjust your boiling point for altitude.

John

I think he's worried about the conductivity of the water throwing off the
measurements, since the wires are bare. I've not had any experience with
thermocouples either; is the difference significant, or should he use
distilled water?

I would guess if he is using ice and boiling water as reference points, he's
not trying to be terribly accurate.

 

"Garrett Mace" <g.ryan@macetech.com> wrote:

"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:0rd4lvckleohjglnbbrgutoieo8ben47oc@4ax.com...
On Sun, 31 Aug 2003 14:32:00 GMT, "K Wind"
kwind@news-server.neo.rr.com> wrote:

I want to build a cold compensation circuit for a type K thermocouple
that I
have. The two wires are soldered together at the end. I plan on using
boiling water and ice water to calibrate. Can I put the end of the probe
into the water just the way it is?

Ken


Sure. But make sure the cold cal is done with lots of well-crushed
ice, stirred frequently. Just some ice cubes in a glass of water can
be pretty far off. And adjust your boiling point for altitude.

John




I think he's worried about the conductivity of the water throwing off the
measurements, since the wires are bare. I've not had any experience with
thermocouples either; is the difference significant, or should he use
distilled water?

I would guess if he is using ice and boiling water as reference points,
he's
not trying to be terribly accurate.


You can calibrate the uninsulated thermocouple by immersing it in water.

The only problem that may occur is if there is any continuity between the
water and some other part of the circuit
e.g. grounded tea kettle containing the water having same ground as measurement
circuit.

If your circuit is battery powered this isn't an issue.

An ice bath made with a distilled ice water bath makes a very accurate zero
calibration point.

The boiling water is a different story.
As mentioned before you have to compensate for altitude.

Long story shot, calibrate your zero with the ice water and the span with
boiling water and you will get reasonable accuracy.

Strill

 

[John Larkin]

On 31 Aug 2003 17:06:13 -0500, <1042241977@127.0.0.1:7501> wrote:

An ice bath made with a distilled ice water bath makes a very accurate zero
calibration point.

I've read the claim that an ice bath made with almost any common tap
water will be within 5 or so millikelvins of zero C, if done
carefully. A thermos bottle, lots finely crushed ice, and enthusiastic
stirring is needed.

John

 

[K Wind]

I actually have two thermocouples. One is welded and the other is bead
welded. If I'm not mistaken, isn't bead welded another name for silver
soldered?

Anyway, what does your answer have to do with whether or not I can put the
damn thing in water?

Ken

"CFoley1064" <cfoley1064@aol.com> wrote in message
news:20030831213220.10672.00000204@mb-m29.aol.com...

I want to build a cold compensation circuit for a type K thermocouple
that I
have. The two wires are soldered together at the end. I plan on using
boiling water and ice water to calibrate. Can I put the end of the probe
into the water just the way it is?

Ken

The soldered connection thermocouple has a number of practical problems.
With
the stress of thermal expansion/contraction cycles, you're going to have a
serious problem keeping a good connection, which can cause you grief. And
remember, you really don't even have a solder joint, because there's no
wetting
of either wire, right? A real welded thermocouple junction can be done
with a
dentist's/jeweller's welder -- ask around. Either that, or precision
bead-welded thermocouples are relatively inexpensive from a number of
sources.
Omega Engineering comes to mind. Look at their 5TC series for 5-packs .

http://www.omega.com/ppt/pptsc.asp?ref=5TC&Nav=tema02

Good luck.

Chris

 

[Bob Masta]

On 01 Sep 2003 01:32:20 GMT, cfoley1064@aol.com (CFoley1064) wrote:

I want to build a cold compensation circuit for a type K thermocouple that I
have. The two wires are soldered together at the end. I plan on using
boiling water and ice water to calibrate. Can I put the end of the probe
into the water just the way it is?

Ken

The soldered connection thermocouple has a number of practical problems. With
the stress of thermal expansion/contraction cycles, you're going to have a
serious problem keeping a good connection, which can cause you grief. And
remember, you really don't even have a solder joint, because there's no wetting
of either wire, right? A real welded thermocouple junction can be done with a
dentist's/jeweller's welder -- ask around. Either that, or precision
bead-welded thermocouples are relatively inexpensive from a number of sources.
Omega Engineering comes to mind. Look at their 5TC series for 5-packs .

http://www.omega.com/ppt/pptsc.asp?ref=5TC&Nav=tema02

Good luck.

Somewhere on the Web I found a description of how to weld
with a car battery and the inside of an old dry cell... tried it and
it works great! You need to pull the carbon rod from an
ordinary (not alkaline) cell. Twist the TC wires together and
clamp the ground from a jumper cable to the twist, near as
practical to the end but not _too_ close. Clamp the positive
lead of the jumpers onto the carbon rod. Then bring the
twisted end of the TC to the rod with a gentle stroke, and
presto...nicely welded TC!


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com

 

[K Wind]

"CFoley1064" <cfoley1064@aol.com> wrote in message
news:20030901142049.17992.00000244@mb-m25.aol.com...

Have fun -- go ahead, put the cold junction in the ice bath. It won't
hurt
anything. Sorry I got on your nerves.

Chris

I don't think you in particular got on my nerves. Sometimes when I post a
question, I get responses and emails that address all kinds of things, but
doesn't answer the question. That's all.

One thing that I should have written better was the description of the end
of the thermocouple. It's bare. As I said before, I have two thermocouples,
one that looks like it's been spot welded and the other looks like it has a
bead of solder. I assumed that it was silver soldered. That's why I used the
word soldered. What I didn't know is if you could stick a thermocouple with
a bare end in water. The calibration is done at room temperature. I want to
check calibration using ice water and boiling water.

Ken