On 18 December 2012 15:31, Crispin Pemberton-Pigott <[email protected] > wrote:
> Dear Steve**** > > ** ** > > I need you to please expand on this for clarity.**** > > ** ** > > *>*The spectrum of the emiission changes, and the sensor materials used > for low temperature IRs can't cope. > > **** > > Do you mean the high temp sensors can’t pick up the low temps? > Yes. The sensor material needed for high temperatures isn't the same as the one for low temperatures, low temperatures are effectively invisible to them,. > Or they have a preferred range? The ones I have used cover -50 to 999. The > ones for house evaluations are about -50 to +250. > > > >I use precision IR thermometers for operation at between 500 and 2000C, > they have no sensitivity below 500C. **** > > ** ** > > Very interesting. I have never had my hands on something that goes that > high. Is the lack of sensitivity because of the need to spread out the > incoming heat to limit damage to the cell? Interesting problem to solve.** > ** > > ** > I don't think so. The numerical aperture is quite high, so they don't admit much energy. Certainlly, where I place mine, 9" from the core of the furnace, imaged through a 10mm hole, I haven't had a problem there at least..... > ** > > Yours must have 4 digits. Maybe more? How accurate is ‘precision’?**** > > We have a good, pure graphite target, emissivity pretty damned close to one. Against type C thermometry, in a reducing atmosphere, at 1800C, we're close to +/- 25 C, we think. BEST measurement, in standards lab conditions (NIST, NPL) at these temps is only +/- 5 deg.
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