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High temp thermometer.

G

Glen Walpert

Jan 1, 1970
0
On a sunny day (Thu, 31 May 2012 15:36:26 -0400) it happened Jamie
<[email protected]>:



Hey, I think you could be wrong.
Not that I am a thermocouple genius, but I did study the subject when I
build by little thermocouple sensor thing, and wrote the soft.
Actually John was a great help suggesting the circuit,
and pointing out stupid errors in my first software release.

If you keep the cold-end sensing where it should be, *at the connector
where the thermocouple wires come in*,
with a sufficient low thermal constant, there should be zero errors.

Well maybe not quite zero but certainly very small, depending on the
accuracy of your CJC compensation. A $200 industrial thermocouple input
module will do this quite well, but a $50 Watlow temperature control
board with thermocouple input will not do a very good job at all, having
a poor CJC circuit located far from the thermocouple connection on the
same terminal block as the power and heater terminals, and management
might not see the value in switching. I am sure there are lots of other
cheap controllers on the market, suitable for +/- 5 C or so, and if you
stick to the $50 category, that is probably all you get.

People have been doing accurate thermocouple measurements in harsh
industrial environments like steel mills for about a century now. I find
it curious that it is still botched so often, even by Omega, one of the
largest manufacturers of thermocouples (some of their cheap TC meters and
controllers are quite poor).
 
J

Jamie

Jan 1, 1970
0
Phil said:
Or you could just throw it in a bucket of ice water to stabilize it. ;)

Cheers

Phil Hobbs
Yeah, but I don't think the controller will like the iced water :)

Jamie
 
K

Ken S. Tucker

Jan 1, 1970
0
Bill said:
Pretentious nonsense.
"Temperature" is an exquisitely well-defined concept in thermodynamics
and quantum mechanics.

Nope.
 
S

Spehro Pefhany

Jan 1, 1970
0
Well maybe not quite zero but certainly very small, depending on the
accuracy of your CJC compensation. A $200 industrial thermocouple input
module will do this quite well, but a $50 Watlow temperature control
board with thermocouple input will not do a very good job at all, having
a poor CJC circuit located far from the thermocouple connection on the
same terminal block as the power and heater terminals, and management
might not see the value in switching.

Ha. I have sample of one of those POS Wat*w controllers that uses a
1N4148 for a CJC and an LM324 for the front end. It's barely good
enough for a pizza oven. But it's got low parts count and other than
accurcy is okay for reliability. The BOM has got to be under $5.
I am sure there are lots of other
cheap controllers on the market, suitable for +/- 5 C or so, and if you
stick to the $50 category, that is probably all you get.

People have been doing accurate thermocouple measurements in harsh
industrial environments like steel mills for about a century now. I find
it curious that it is still botched so often, even by Omega, one of the
largest manufacturers of thermocouples (some of their cheap TC meters and
controllers are quite poor).

Lots of folks don't need any better than a reliable 5-10°. The specs
also tend to be misleading the way they define the errors.


Best regards,
Spehro Pefhany
 
J

Jamie

Jan 1, 1970
0
George said:
"even by Omega, one of the
largest manufacturers of thermocouples (some of their cheap TC meters
and
controllers are quite poor)"

"Rut row" (In the voice of the dog on the Jetsons)

Care to share any specific model numbers? Maybe I better get out the
heat gun tommorrow.

George H.

Now wait George, I much behave myself here, my employer sells products
to them ! :)

Jamie
 
J

John Devereux

Jan 1, 1970
0
Jan Panteltje said:
On a sunny day (Thu, 31 May 2012 15:36:26 -0400) it happened Jamie
<[email protected]>:



Hey, I think you could be wrong.
Not that I am a thermocouple genius, but I did study the subject when
I build by little thermocouple sensor thing, and wrote the soft.
Actually John was a great help suggesting the circuit,
and pointing out stupid errors in my first software release.

If you keep the cold-end sensing where it should be, *at the connector where the thermocouple wires come in*,

Absolutely, this is the key point which he has not even mentioned - so I
suspect he does not realize the importance of it.
 
S

Spehro Pefhany

Jan 1, 1970
0
Well that's mostly true for the TC stuff I've done. Most of the time
the controller is near room temp. But next time I turn on one I'll
blow a little heat on the controller and see if there's any change.

George H.

That's not entirely fair.. you really should not be blowing hot air on
the controller. It's okay to heat it up in a closed box, but they are
assuming a certain relationship between the CJC sensor and the
terminal block.

In an industrial type design, the guts are usually designed to plug
in, there are cost constraints, and typically the input is "universal"
which precludes the use of thermocouple materials on the terminals. So
you end up with a sensor that's rather loosely thermally connected to
the terminals, and an assumption about the gradient from the heat
disspated by the instrument.

You can do orders of magnitude better if those constraints are relaxed
(but it will be a different kind of beast).
 
G

Glen Walpert

Jan 1, 1970
0
"even by Omega, one of the
largest manufacturers of thermocouples (some of their cheap TC meters
and controllers are quite poor)"

"Rut row" (In the voice of the dog on the Jetsons)

Care to share any specific model numbers? Maybe I better get out the
heat gun tommorrow.

I don't recall specific model numbers, and haven't bought anything from
Omega this century, but I recall a line of low cost plug-in temperature
controllers where the CJC compensation was quite far and well insulated
from the thermocouple terminals. Whereas the CJC on the Analog devices
5B plug-in modules was right at the thermocouple terminals on the
backplane, not in the modules. If your CJC is far enough from the TC
terminals that you can heat one without heating the other, you will have
an accuracy problem in other than a benign, near constant temperature
environment, so if you can see where the CJC is you can predict the
results of the heat gun test.
 
S

Spehro Pefhany

Jan 1, 1970
0
Grin... I should have read this before 'wasting' my morning f-ing
around.
As you say this should be in a 'thermal' box. Blowing hot air (and
freeze spray) around I could get the display to go in different
directions depending on where I blew the air. Onto the input pins the
displayed temp would rise, into the body of the controller and it
would decrease. So thermal gradients are bad!

The spec sheet lists the CJC as 0.05C/C (1/20)

That's actually pretty decent, as these things go. So 20°C delta
should affect the reading by less than 1°C**
A belated thanks Spehro,
George H.

No problem!

** well, not really, they'll fudge the spec by seperating out the
input drift from the compensator tracking, but that's another story.
 
J

Jamie

Jan 1, 1970
0
Glen said:
I don't recall specific model numbers, and haven't bought anything from
Omega this century, but I recall a line of low cost plug-in temperature
controllers where the CJC compensation was quite far and well insulated
from the thermocouple terminals. Whereas the CJC on the Analog devices
5B plug-in modules was right at the thermocouple terminals on the
backplane, not in the modules. If your CJC is far enough from the TC
terminals that you can heat one without heating the other, you will have
an accuracy problem in other than a benign, near constant temperature
environment, so if you can see where the CJC is you can predict the
results of the heat gun test.

We have a controller at work the lab uses, it has an optional CJ input
so you can use an external CJ. That works very nicely. It actually is
required in a test they run for some MIL spec product. The process
controller is actually sitting out side the test cubical.

Jamie
 
R

Ralph Barone

Jan 1, 1970
0
Glen Walpert said:
Well maybe not quite zero but certainly very small, depending on the
accuracy of your CJC compensation. A $200 industrial thermocouple input
module will do this quite well, but a $50 Watlow temperature control
board with thermocouple input will not do a very good job at all, having
a poor CJC circuit located far from the thermocouple connection on the
same terminal block as the power and heater terminals, and management
might not see the value in switching. I am sure there are lots of other
cheap controllers on the market, suitable for +/- 5 C or so, and if you
stick to the $50 category, that is probably all you get.

People have been doing accurate thermocouple measurements in harsh
industrial environments like steel mills for about a century now. I find
it curious that it is still botched so often, even by Omega, one of the
largest manufacturers of thermocouples (some of their cheap TC meters and
controllers are quite poor).

There needs to be SOME reason to buy their more expensive controllers...
 
J

John S

Jan 1, 1970
0
You know what, I've work with this shit long enough to know the
difference on wire connections. You guys act like you never leave the
controlled environment. Red = (-), white (+) for J and yellow (+) For K
etc...


That's one of your problems. You work with shit. Try working with
electrical stuff for a change.


This is all basic stuff to me, I don't understand why it is such a hard
concept for others.

jamie

That's your another of your problems. You think you know it all and no
one is your equal. As a result, you won't listen to experts who are
trying to help you.
 
J

Jamie

Jan 1, 1970
0
Ralph said:
There needs to be SOME reason to buy their more expensive controllers...

Not to long ago, we looked at some funky looking seebeck controller,
instead of the terminals or connection for the couple on the device, It
comes with a jumper assembly that allows you to install the jack on the
outside of the panel. This assembly has both temp sensor and the
thermocouple terminations at the jack. This keeps the two together where
it matters.

The problem is, it is not a panel mounted device with display. These
are din rail only and a slew of communication options to talk to it..

Jamie
 
J

Jamie

Jan 1, 1970
0
John said:
That's one of your problems. You work with shit. Try working with
electrical stuff for a change.




That's your another of your problems. You think you know it all and no
one is your equal. As a result, you won't listen to experts who are
trying to help you.


As for you, I work with what ever my employer allows me to purchase with
the budget for that job. If it can be gotten as a common item, that is
what takes place. If not, it gets built.

As for me thinking that I know it all? That opinion usually comes from
those with a insecurity problem?

I've never claimed to know it all. I don't, Because I am intelligent
enough to know the difference. I am proud of what I do know because it
was hard work all these years that got me where I am. And I for one,
think I have done very well over the years.

However, there are those that are just leaches and get upset when
they find out they aren't the only kid on the block. Kind of common
here, wouldn't you say? Something you should be familiar with.

Jamie
 
K

Ken S. Tucker

Jan 1, 1970
0
Bill said:
STP stands for standard temperature and pressure - 20ºC in Europe and
Australia, 25ºC in the US though there are other interpretations.

http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure

If there's a current running through the wire in such a standard
environment, it will be warmed by resistive heating and cooled by
radiation, conduction and convection. Since you haven't specified the
orientation of the wire,

Length is not NOT height.
Ken
 
K

Ken S. Tucker

Jan 1, 1970
0
John said:
I know! I know! (Waves hand furiously.)
0 C!
I guess Bill didn't redeem himself very well.

I missed the part about turning on the switch!
Seriously though, Mr. BS is entirely unaware of most of
thermal technology such as...
http://en.wikipedia.org/wiki/Pyrometer
I needed just one question to rat out the charlatan.
Ken
 
I've got more patents than you have, so presumably I've got rather
more functional imagination.

I have more patents that you do, but that has nothing to do with the fact that
you're a dumbshit.
You, of course, use your imagination where anybody with any sense
would search out real world facts ...

It would seem his imagination keep him in business, employing several good
people. You?
 
F

Fred Abse

Jan 1, 1970
0
Thermocouples aren't sensitive to EMI!

But the circuits they connect to can be. Once cost me a week's work
finding out that a controller's erratic behavior was due to RF crap from a
thyristor bank getting into a thermocouple input, on a brand new piece of
plant. The maker's commissioning engineer had run away, screaming for
Mommy, (well, screaming for their R&D guys, really), The customer couldn't
wait. I suppose I should have asked for twice what I actually got.
 
J

John S

Jan 1, 1970
0
Krw is so dumb that even the other right-wing nitwits have noticed,
and he thinks that his patents - filed by the IBM patent department in
its ceaseless search for valueless patents to throw into patent=swap
agreements - are worth the paper they were printed on.


It's his imaginative claims that he produces "insanely good"
electronics that keep him in business, peddling pedestrian bespoke
electronics to people who don't know any better.

I'm honest and realistic, which blocks that particular option.

Bill, what is your present income from the products you have personally
designed and are shipping?

Just curious.
 
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