One of the unsolved problems I still have is measuring temperature in furnace at $700-1100^\circ\mathrm{C}$ range (I need some $\pm0.1\%$ repeatability and $\pm1\%$ 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 $~400^\circ\mathrm{C}$.

I've checked blackbody emission for $700-1100^\circ\mathrm{C}$ objects, and it seems that even at $500^\circ\mathrm{C}$ objects start to emit at $1\,\mu\text{m}$ range (not much though), which is easily measurable by cheap silicon photo-diodes (ones I have on the desk have maximum at $880\ \mathrm{nm}$, with $70\%$ sensitivity at 1um and $10\%$ at $1.1\ \mu\text{m}$, 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 $\mathrm{PbS}$ photoresistor ($2.1\,\mu\text{m}$ maximum), but they are not that precise, quite expensive and scarce. What are your thoughts or suggestions?


1 Answer 1


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.

  • $\begingroup$ I got it a surplus for 35$. There out there. $\endgroup$
    – Fortunato
    Jul 7, 2011 at 1:22
  • $\begingroup$ 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 ) $\endgroup$ Jul 7, 2011 at 6:54
  • $\begingroup$ The TJ36-CAXL-316U-6-CC-XCIB is a ceramic insulated type K probe it will do the job for $51 $\endgroup$
    – Fortunato
    Jul 7, 2011 at 19:20
  • $\begingroup$ 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... $\endgroup$ Jul 7, 2011 at 22:42
  • $\begingroup$ For future generations: This answer has nothing to do with pyrometers :-D $\endgroup$ Jul 22, 2011 at 20:32

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