[Stoves] Infra-red thermometer choice and supply

[Steve Taylor]

On 18 December 2012 15:31, Crispin Pemberton-Pigott <crispinpigott at gmail.com
> 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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