Trying to use a silicon PD for that temperature range is difficult,
because there's so much more long-wave IR than there is short-wave. The
usual rule of thumb is that a dark surface just begins to have a visible
red glow at 900 F (~500 C).
The most generally useful black body function for this sort of job is
n_lambda(T, lambda), the number of photons emitted per square metre per
second per unit wavelength. It is given by
n_lambda(T, lambda) = 2c/(lambda**4*(exp(h*c/lambda/k/T)-1)).
Integrating that over lambda between 0.3e-6 and 1.1e-6 (the silicon
band, being generous) and over the flat surface of the 0.09 inch square
photodiode (1.25e-7 sq m) gets you the following amount of photocurrent:
T(C) Iphoto(300-1100 nm)
(hemisphere) f/8 aperture
---------------------------------------------
500 8.4e-08 0.33 nA
550 2.5e-07 0.99 nA
600 6.7e-07 2.6 nA
650 1.6e-06 6.2 nA
700 3.5e-06 14 nA
750 7.2e-06 29 nA
800 1.4e-05 54 nA
850 2.5e-05 98 nA
900 4.4e-05 170 nA
950 7.2e-05 0.28 uA
1000 1.2e-04 0.45 uA
Thing is, you can't use anything like a whole hemisphere's worth, or the
apparatus will melt very rapidly, just as though it were attached to the
hot object. So assuming that you can actually manage an aperture of f/8
(0.012 steradian vs pi steradians for the hemisphere), you get the third
column's worth of photocurrent. This of course neglects the visible
light filter and other optical inefficiencies, which will reduce these
numbers some.
Your detector has a built-in 1M feedback resistor, so you're pretty well
down in the mud at the lower end of your range, and will have problems
with ambient light. A chopper wheel will help a lot with the DC drift,
but not with the ambient light, because that'll get chopped as well.
A nice black bolometer (thermistor) will do a better job in this range,
because almost all the photons are outside the detector's range.
Pyrometry isn't that easy to do well.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net