Directly Measuring High Temps

[D H B]

Who has experience/recommendations with thermocouples+thermowells on the high side of the R/S/B range?

[lawman]

R/S/B range???

[BIGGUNDOCTOR]

Here is a link for Omega, a company we used when I worked at various places. It has info for choosing the right one.

http://www.omega.com/prodinfo/thermocouples.html

If you are looking at these, are you looking at some high temps? The B goes to 3100° F. With a high of up to 97% platinum content, and rhodium as a filler, they are not going to be inexpensive.

[timgunn1962]

I've not used B. I have used both R and S. The application was/is direct fired thermal oxidizers running on landfill gas and the process temperature was 1200 degc (2192 degF) . We've since reduced the process temperature to 1000 degC (1832 degF) and tend to fit Type N now.

In essence, it works like a big gas forge. The gas flow is set, then air supply is adjusted to get the temperature required. It gets a bit more complicated than a gas forge because the gas flow is variable, but it's pretty boring.

The Type S thermocouples have had 3/8" to 1/2" diameter Recrystallized Alumina sheaths and Stainless Steel support tubes. They are inserted through the wall and are horixontal in use. Apart from needing to be stiff enough to self-support over about 12" of insertion depth, there  is no real need for mechanical strength and it's an open-topped chamber so pressure is negligible.  I've therefore not used thermowells.

I've repurposed one of the type S thermocouples for measuring forge temperatures when I've been playing with burners

If you've got any specific questions I might be able to help with, I'll try to answer them. The best advice I can give is to write down what you need (as distinct from what you think you want), make a nice strong cup of tea/coffee, pick up the phone and sit down for a chat with Omega. They are specialists in temperature measurement and control and deal with this stuff regularly. If you have a local thermocouple manufacturer, talk to them as well (not instead of)

I've not been keeping up-to-date on IR temperature measurement, but it was looking like it would give pretty good results when looking at the inside of a thermowell or similar, since a hole has an emissivity of 1.0. It may be worth bearing in mind.

[D H B]

That's the second & third recommendation for "Talk to a Sales Engineer at Omega" I've received ( I'm asking all-of-everybody ).  Seems like it's probably the right way to go.

Definitely I'm looking at what I want, not what I need   What I 'need' is to print out a steel color chart.  What I -want- is +-~5C at a glance up to ~1600C sustained.

My understanding ( limited ) is that Type B Pt/Rh with al2o3 insulator + sheathe should probably get me there, and a larger probe will react slower than a small one.  Makes sense ( I think? )

Edited April 19, 2015 by D H B
add missing opening paren

[timgunn1962]

It's still not really clear what you are after, though you've certainly narrowed it down.

How are you intending to heat?

If you are using a furnace, whether gas or electric, the usual way of getting the steel to a given temperature is to set the furnace temperature and monitor it, then wait until the steel is the same colour as the forge interior. If you are doing this, you can perhaps be a bit more accurate if you put the thermocouple in front of the steel and watch it until it disappears  against the steel.

I am fairly sure Type R,S or B should get you a temperature reading and I think the Recrystallized Alumina sheath should do it. As you say, generally speaking, and for a given sheath material, the thinner the sheath, the faster the response.

If you are taking the steel out of the furnace, heating with an induction coil or doing anything else strange, get a good description of your process down on paper before you talk to the experts. I think there will be several more variables to consider, possibly including emissivity, once you are outside the furnace.

I had an IR thermometer that would measure to 1600 degC a while ago. It worked and I was quite impressed by it. Ultimately, it was not much good for my purposes because  I was dealing with unknown and variable emissivity as the surface scale changed. I could not just shoot the temperature while the workpiece was in the forge (and emissivity therefore at 1.00) due to interference from the gas flame. I passed it onto a smith who finds it useful: I think he uses it to check he is within a temperature range when making Damascus, so he doesn't need absolute precision. I don't have details.

http://www.digital-meters.com/temperature-c3/infrared-thermometers-c17/cem-high-temperature-infrared-thermometer-50-to-1600-c-cem-dt-8859-p250

Edit: Pure Iron melts at 1538 degC and steels melt at lower temperatures. Things are likely to be dribbly before you get to 1600 degC.

Edited April 19, 2015 by timgunn1962

[ianinsa]

I have been using k type thermocouple units for many years then about 2 years ago John E from Gearhart let me use his IR 'gun' and ......SOLD.

I currently have 3 brand new unused 'k' types sitting in boxes and the Infrared ones get used all the time, for me at $100 its just a no brainer! But its horses for courses all the way

[D H B]

This is the portion I'm currently trying to solve , though I'm fairly certain I'm going about asking it all wrong  

Scale and/or flame interference potentially preventing accurate measurement is the reason I'm wanting to measure the gas temps inside instead of a touchless.

I have no plans for intentionally melting iron or steel today, but if I'm spending a largish sum on a measurement tool I definitely want it to include the capability for Future Bad Ideas.

set the furnace temperature and monitor it

[D H B]

Wow, I completely missed the IR-gun-plus-thermowell bit earlier.  That's actually really intriguing.

[D H B]

Thanks for the discussion, everyone.  So far the winner is an al2o3 thermowell, then measuring the inside surface of that thermowell with an IR gun.

Any recommendations on a particular IR gun?

[swedefiddle]

Good Morning,

There are lots available up to about 500c. I have been using one for quite a while, you just have to wait until you find one in your price range.

Neil

[ianinsa]

This is a picture of John E's  IR gun about $100 plus shipping I get mine DHL direct from China, different make and it works really well PM me if you need info, mine cost a bit less and the agent has sent me standard k' types as well the upside is he does paypal and you actually get the stuff!

[D H B]

That seem like almost exactly what I'm looking for, and the price certainly sounds attractive 

I was looking at the Benetech GM1650 , but I'm not certain it has the ability to take a thermocouple.

@ianinsa : sent you a PM, and thanks!

[ianinsa]

These are what I use and I love them!

[ianinsa]

The everyday model

[D H B]

To anybody following along: ended up with a very good deal on the Benetech GM1650 .  Doesn't take a thermocouple, but for the price I'm not complaining 

[the iron dwarf]

am expecting  mine to arrive tomorrow, it is at the DHL local depot, great price and fast delivery.

 

next is to find an easy and reliable way to use it with a forge burning coke, may try burying a piece of high temperature ceramic in the fire, uncovering it and pointing at that rather than hit and miss on hot coals or scale on metal giving random results.

will have a play next time the forge is in use

[ianinsa]

Should have asked Raymond for a 'k' type thermocouple

[the iron dwarf]

well I do have lots of uses planned for this, my current one only goes to 600c so for the cost I am glad to have the higher range, I may be buying more items later ( also just got a 15 kw induction heater last week )