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?