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One of the unsolved problems I still have is measuring temperature in furnace at 700-1100C range (I need some +-0.1% repeatability and +-1% precision).

Obviously, contact thermometers are quite rare & expensive for this range, everything I was able to find is rated at 450-500C max (especially as this should work in aggressive oxygen/ozone/chlorine atmosphere).

Consumer grade pyrometers does not work above ~400C.

I've checked blackbody emission for 700-1100C objects, and it seems that even at 500C objects start to emit at 1um range (not much though), which is easily measurable by cheap silicon photo-diodes (ones I have on the desk have maximum at 880nm, with 70% sensitivity at 1um and 10% at 1.1um, visible light filtered).

As my target is always the same with fixed emissivity, there should be no vital need for 2-band measurement.

Are there any issues with this single-band temperature measurement approach? Alternatively, I might add PbS photoresistor (2.1um maximum), but they are not that precise, quite expensive and scarce. What are your thoughts or suggestions?

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this one goes up to 1000C: technodepot.com/product/view/product/… –  user2963 Jul 18 '11 at 16:34
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+50

I am using a CN7600 in my furnace. Omega 76000 This controller is very accurate. As for all them measurements I have made it keeps the oven 750 C. It fluctuates from 750 to 751 which just over 1% if I take 750.5 as my required temperature. Now whit a little improvement in the furnace design I can improve this. The problem is eliminating "Hot pockets" in the furnace by having a very mild air/gas flow around the subject. The prove wires can be in a Pirex tube for temps under 1000 C and the controller can compensate for this.

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I got it a surplus for 35$. There out there. –  Fortunato Jul 7 '11 at 1:22
    
As far as I see, it require separate RTD probe which at these temperatures have to be made out of quartz & platinum, and this is the main problem ) –  BarsMonster Jul 7 '11 at 6:54
    
The TJ36-CAXL-316U-6-CC-XCIB is a ceramic insulated type K probe it will do the job for $51 –  Fortunato Jul 7 '11 at 19:20
    
Good suggestion... Checked alibaba and found several suppliers there who can ship high-temperature K-sensors. This might be nice addition especially for calibration, but I still want to pursue IR way as I would need very aggressive heat profiles (some 50-100C/sec) - and contact probes are too slow... –  BarsMonster Jul 7 '11 at 22:42
    
For future generations: This answer has nothing to do with pyrometers :-D –  BarsMonster Jul 22 '11 at 20:32
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