Question about a thermometer

[Scott.Rapp]

I was looking at some thermometers that I could carry around with me for checking the temp of my forge, and my steel and everything ... out of curiosity... would this work well? Any other suggestions?

 

http://www.keenzo.com/showproduct.asp?M=EL...8258&ref=GB

[Howard Clark]

Yes, that one will read high enough temperatures to do heat treating of simple carbon and low alloy steels. That is the first one I have seen in this price range that has a high enough top end. Thanks for posting that. I may have to buy one of those for myself.

[P.Abrera]

How does something like that work? Point at what your measuring and take a reading (radiant heat)? Will it work for liquids (like hot oil)?

[Glenn Moulton]

It uses infrared.They have become very popular with welding inspectors checking preheat temps prior to welding.Specially the over weight ones who find it hard to bend over and use the tried and proved tempstix.

[Scott.Rapp]

Yes, that one will read high enough temperatures to do heat treating of simple carbon and low alloy steels. That is the first one I have seen in this price range that has a high enough top end. Thanks for posting that. I may have to buy one of those for myself.

 

Oooo, cool. That makes me happy to know

 

I'm always wondering what the temp in my forge is ..

 

Do most of you forge in a dark area, or outside? I forged a good bit outside in the sun, but it's hard to tell the temp there. The one time I forged at night, it was so easy to tell the color of the steel, and everything. I'm always afraid I'm gonna WAY overheat ...

[Steve R]

Sweet, thanks for posting that! I just ordered one from here: http://www.ntxtools.com/network-tool-wareh...75-p-ESI01.html

 

It's a little cheaper than the first link.

 

cheers,

/steve

[Howard Clark]

Full sun is a very difficult environment for forging. For exactly the reason you mention.

[RedNeckLeftie]

Hi Guys,

 

You need to be VERY careful using any of these IR/Black-Body temp units. Their accuracy is at best very, very loose. The best unit I have seen (~$500) was about 0.75% basic accuracy. If it read 1550F, the "real answer" was 1538-1561F. Now, that is under "perfect" circumstances.

 

These units rely on a physics property known as "Black-Body" radiation. Basically, it means that an "anus" of space, in a vacuum, will radiate a specific amount based soley on its thermal energy (what we usually call temp). If, however, something other than space is being heated, the radiation (light emission) will change. The amount of change from ideal vacuum is referred to as emissivity.

 

The high-end IR temp units will have an adjustable emissivity (to compensate for your particular target material), but this is not enough. It turns out that emissivity for a given material, including steel, changes with temperature! (Steel emissivity can vary from 0.07 to 0.85 depending on alloy, rust, level of polish, and temp from 200-3200F.)

 

I originally thought these things would be the cat's @ss for gauging quench temps, then I cranked the numbers--it is not a pretty picture.

 

Best of Luck and Wishes,

Brian K.

[Scott.Rapp]

Hi Guys,

 

You need to be VERY careful using any of these IR/Black-Body temp units. Their accuracy is at best very, very loose. The best unit I have seen (~$500) was about 0.75% basic accuracy. If it read 1550F, the "real answer" was 1538-1561F. Now, that is under "perfect" circumstances.

 

These units rely on a physics property known as "Black-Body" radiation. Basically, it means that an "anus" of space, in a vacuum, will radiate a specific amount based soley on its thermal energy (what we usually call temp). If, however, something other than space is being heated, the radiation (light emission) will change. The amount of change from ideal vacuum is referred to as emissivity.

 

The high-end IR temp units will have an adjustable emissivity (to compensate for your particular target material), but this is not enough. It turns out that emissivity for a given material, including steel, changes with temperature! (Steel emissivity can vary from 0.07 to 0.85 depending on alloy, rust, level of polish, and temp from 200-3200F.)

 

I originally thought these things would be the cat's @ss for gauging quench temps, then I cranked the numbers--it is not a pretty picture.

 

Best of Luck and Wishes,

Brian K.

 

Care to share a better way to check temperature in the forge and everything? I was looking at perhaps getting a thermocouple type thing ... but I couldn't find much in the way of that. Anyone have setups that are more accurate, or is the IR reader gonna be about the cheapest to go to get a somewhat accurate reading?

[Bennett]

I've played around with those at work. The maintainence guys use them to measure motor temps and such. I had the same idea about the heat treatment. They seem to "average" out an area and jump around a lot. I pointed them at a mercury vapor light and got readings that varied by about 900 degrees with very little movement of the gun. Use with caution.

[Steve R]

Hi Guys,

 

You need to be VERY careful using any of these IR/Black-Body temp units. Their accuracy is at best very, very loose. The best unit I have seen (~$500) was about 0.75% basic accuracy. If it read 1550F, the "real answer" was 1538-1561F. Now, that is under "perfect" circumstances.

 

These units rely on a physics property known as "Black-Body" radiation. Basically, it means that an "anus" of space, in a vacuum, will radiate a specific amount based soley on its thermal energy (what we usually call temp). If, however, something other than space is being heated, the radiation (light emission) will change. The amount of change from ideal vacuum is referred to as emissivity.

 

The high-end IR temp units will have an adjustable emissivity (to compensate for your particular target material), but this is not enough. It turns out that emissivity for a given material, including steel, changes with temperature! (Steel emissivity can vary from 0.07 to 0.85 depending on alloy, rust, level of polish, and temp from 200-3200F.)

 

I originally thought these things would be the cat's @ss for gauging quench temps, then I cranked the numbers--it is not a pretty picture.

 

Best of Luck and Wishes,

Brian K.

 

Well, this one has a spec'd accuracy of +/-1.5%, which translates to +/-22 degrees at 1500. Probably still better than my eye and a magnet. Still, I may try doing some quick and dirty calibration with it against a thermocouple or two when I get it to see how far it's off, how linear it is, and if it's consistent. Thanks for the heads up.

 

cheers,

/steve

[Scott.Rapp]

Well, this one has a spec'd accuracy of +/-1.5%, which translates to +/-22 degrees at 1500. Probably still better than my eye and a magnet. Still, I may try doing some quick and dirty calibration with it against a thermocouple or two when I get it to see how far it's off, how linear it is, and if it's consistent. Thanks for the heads up.

 

cheers,

/steve

 

mind reporting back to us about your testing? I'd be curious to see some hard data on it

[RedNeckLeftie]

Hi Steve,

 

I believe that unit also has a fixed emissivity of 0.95. The point I was trying to make earlier (and kinda failed at) was that the emissivity can severely impact the accuracy of the measurement. While the unit may have a basic accuracy of 1.5%, the "practical" accuracy could be as bad as 30-50%, especially above 1000F--like Bennett's experiments above.

 

One thing these IR manufacturers suggest it to make/leave a hole in the "work," and take a measurement of the temp of the hole, since this will closely approximate a black body radiator. The hole obviously has to be at least as big as the unit's field-of-view at the given measuring distance.

 

Personally, I would recommend thermocouples for temp sensing. They tend to be very accurate, and are not impacted by external considerations. These can be had from Omega (www.omega.com). Some thermocouples can even be hooked to a digital multimeter, where the voltage indicates the temp. I use an electric HT oven, so mine came with a thermocouple--might check Paragon's web site to see if they sell thermocouples as spares...

 

Thanks,

Brian K.

Edited August 4, 2008 by RedNeckLeftie

[jhobson]

I use a cheap meter with a good thermocouple.

Could try a cheap thermocouple as well e.g:

http://shop.ebay.co.uk/?_from=R40&_trk...kw=thermocouple

and

http://cgi.ebay.co.uk/DMM-Multimeter-Temp-...86.c0.m14.l1318

[Steve R]

Hi guys,

 

I understand the issue with emissivity, which is why I want to do some calibration runs to see how non-linear the results are (due to the change in emissivity of steel at different temperatures). I doubt the reading will be off by anywhere near 30 - 50%. I'd be interested to know what distance Jerry took those measurements at, and what the spot-to-distance ratio of the unit he was using is. This also has the potential to greatly affect accuracy, possibly more than any of the other factors combined. I hear what you're saying, I just don't think it will be quite that bad and as I said I plan on doing some testing to see how bad it is. I'll post results when I have them.

 

As for the thermocouple, I do use a k-type in my tempering oven, but my forge isn't exactly temperature controlled so the temp of the forge isn't very useful to me - I want to know the temp of the steel itself. Trying to use a contact thermocouple in a forge is not my ideal solution (though I may try rigging something that I can poke different parts of the blade against at some point to see how well it works). I also need to get an r-type as k-types aren't as linear or accurate in the forging/heat treating temp ranges.

 

[edit] Haha! Make that I wish I could get an r-type! Those things ain't cheap! [/edit]

 

cheers,

/steve

Edited August 4, 2008 by Steve R

[RedNeckLeftie]

Hi Steve,

 

I have to keep reminding myself this is a blade-FORGING group (for the most part; I am a "lowly" stock-removal fella). After re-reading the posts, I understand the predicament, and that thermocouples would not be the cleanest solution. Thermocouples tend to take their own sweet time stabilizing on a temp reading, about 35 secs.

 

I certainly hope you are successful with the IR thermo, please do post your results. If it's good enough, I may have to spring for one as a backup check.

 

Thanks,

Brian K.