Ping Karl!

OOps, those are Platinum resistance temp. detectors, NOT thermocouples.

Jon

Don Foreman has the equipment to help here. I'll ask him and email you.

Karl

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A thermocouple is a twin-lead junction of two dissimilar metals that generates a voltage differential as a function of temperature changes ("the thermoelectric effect").

A resistance temperature detector (RTD, commonly) is a single material/alloy whose resistance varies w/ temperature.

In the former one measures the generated voltage; in the later one measures resistance. Each then uses a calibration curve to relate the output to temperature.

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Further, a great many temperature controllers will accept multiple types of sensing elements with appropriate configuration.

Do you have more of the platinum ones? It would be good for me to swap that in (or at least have it on hand to swap in when the type K burns out.)

Thanks, DoN.

Most reasonably modern temperature controllers will use those. Yes, they are not thermocouples, which need a junction of two dissimilar metal alloys -- such as Chromel and Alumel, or Iron and Constantan. I'm not sure whether either of those may be what is called Type-K, but I think that the first may be.

Yes Platinum are variable resistors, not true thermocouples. But a good controller should be configurable for many types of temperature detectors. And the Platinum resistance ones are (I believe) the best for life at high temperatures. (So my just posted question still stands, even though I missed that you called them thermocouples instead of thermo-sensors. :-)

Enjoy, DoN.

Thermocouples are made of a welded junction of two dissimilar metals, and generate a tiny voltage proportional to absolute temperature.

Resistance temperature detectors are resistors whose value changes with temperature, so you have to put some current though one and measure the voltage resulting from that current to know the temperature. No problem, most modern controllers can handle either type, only requiring reconfiguration of a parameter in some interminable menus. :-)

Enjoy, DoN.

On 5/29/2012 10:29 PM, DoN. Nichols wrote: ...

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Yes Type-K is chromel-alumel. They're good to the Curie point of about

Platinum is the premier RTD material for almost all purposes...

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I pretty much switched to rtd's in r&d due to their better accuracy and stability. I had thermocouples drift a few degrees/year in extruder service with daily temperature cycling to 200+ C. There are two main rtd calibrations that I am aware of, European or American. There is a slight difference in temperature coefficient between the two. You need to know which you have when you set up your controller.

Pete Keillor

On 5/30/2012 12:13 AM, Gunner Asch wrote: ...

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If they're Pt, they're RTDs as J--

Platinum RTDs are best for moderately high temperatures (maybe up to

Almost everyone uses the Euro standard (alpha = 0.00385) RTD these days. I have not seen the old US style 0.00392 type in ages).

There's not much platinum in an RTD these days, well under $1, since just a thin film is generally used (sealed under a glass passivation).

Platinum (actually Platinum/Platinum-Rhodium alloy) THERMOCOUPLES are such as type R and S are best for very high temperatures (over

Yeah, seems like I standardized on 385's about 15 years or so before I retired. However, if Jon's are old stock, it would be important to know their calibration. Back then, my controllers could handle either. Don't know if that's still the case or not.

Gunner Asch on Tue, 29 May 2012 23:22:20 -0700 typed in rec.crafts.metalworking the following:

Sure some wasn't Misc? Not to be confused with "Misc Stuff". Or Assorted Stuff, which of course is different than Unsorted Stuff, Various Stuff, and Unlabeled Stuff .

I think I may still have boxes from three moves back marked "desk stuff". And one marked "It's 3 AM, who knows?"

On 5/30/2012 9:13 AM, Gunner Asch wrote: ...

What about some of these, maybe????

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Sent via private e-mail. Let me know if you don't get it for whatever reason (which may be that my message never reached you, or vise versa) -- and proably best via a message here, since sometimes emails which I've expected to you have vanished in mid-transfer.

Thanks, DoN.

You appear to have the variable resistor type. Most controllers should handle them. The voltage generator type would need some other metal as half of the sensor element.

Not much that I can trim in this followup and keep the context for other readers. Sorry.

Good Luck, DoN.

Hi Pete Keillor and/or anyone on RCM

Recently I've sent a couple of messages to RCM to test the waters, so to speak. If anyone sees this test post of mine, please respond through a a normal RCM post. Thanks.

Bob Sw>>

Yeah, seems like I standardized on 385's about 15 years or so before I retired. However, if Jon's are old stock, it would be important to know their calibration. Back then, my controllers could handle either. Don't know if that's still the case or not.

Hi, Bob.

Pete Keillor

I see it. I trimmed all the unrelated quoted material in this followup.

Enjoy, DoN.