High temp thermometer.

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Ken, you might have understood physics once, but those days are behind you. Carrying on as if you actually understand General Relativity and Quantum Mechanics may make you feel better, but - sadly - you obviously haven't got a clue.

-- Bill Sloman, Nijmegen

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.

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

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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Thanks John, It's an Omega 'thing' so I hope not. We should be paying for something.

** I hate all the sniping on SED. I come here to learn something, solve problems, and help if I can. Word's of wisdom, drummed into me by my Welsh Grandmother, "If you can't say something nice, it's usually better to say nothing at all."**

That's not directed at you, but all the SED... I've thrown stones of my own, and am not without sin.

George H.

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"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

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.

years ago.

magnetic bearing module

your temperature sensors.

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John Devereux

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).

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.

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)

A belated thanks Spehro, George H.

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Thanks Glen, Its a little CNi32 series controller. It's impossible to see any of the circuitry, but I did find out the CJC is not that close to the terminals. (See reply to Spehro) Mostly fine for my application, as there's not a lot of heat generated inside the electronics box, so not a big gradient.

George H.

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

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.

Maybe twice,

Which proves my point, Mr. BS, you've never understood temperature, except on a very primitive level, which is evidently good enuf for you. This AM I read two articles on the subject, one needs to be a mathematical physicist to even be aware of the problems. Ken

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

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Redefining "proof" in a new, but less-than-interesting way.

Who am I to argue with the scientific establishment, who seem happy accept the concept you reject as "ill-defined"? They gave me a Ph.D., which is more recognition than you managed to get, so perhaps I'm prepared to cut them more slack than you are.

And how would you know that? You claim to have been a mathematical physicist once upon a time, but can't point to any evidence documenting this status. You have pointed to stuff on the web which suggests that you "collaborate" with Einstein-was-wrong-and-I-can- prove-it fruitcakes, but your insights - such as they are - don't seem to make into the peer-reviewed literature.

Pushing out waddle about temperature being an ill-defined concept is just more of you being a pretentious twit.

-- Bill Sloman, Nijmegen

In my class, I would 'give' you the D, as in Dull. Most others *EARNED* their marks, but I'm a hard marker so best off stay in your sissy school.

I will however give you an opportunity to redeem yourself... Given NiCr wire with length L, dia. D and current A, what is the temperature of such a wire (assume STP). Professor Ken S. Tucker

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

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So you would be as incompetent as a teacher as you are in everything you let us see here.

STP stands for standard temperature and pressure - 20=BAC in Europe and Australia, 25=BAC in the US though there are other interpretations.

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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, we can't say anything particularly useful about convective cooling - which is likely to dominate unless wire is very thin - so it's a silly question, as we'd expect from you.

-- Bill Sloman, Nijmegen

I know! I know! (Waves hand furiously.)

0 C!

I guess Bill didn't redeem himself very well.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

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.