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Kirchhoff,
Gustav
Gustav Kirchhoff (1824–1887) developed the physics foundation for many of
the concepts for which pyrometry and optical thermometry are based. He was
the first to describe the blackbody in 1859-1860. Kirchhoff’s Law correctly
describes the way objects emit and reflect light as a function of angle and
wavelength.
Lightpipe
A rod typically made from sapphire or quartz which acts as a guide to “pipe”
light from a hot object back to a fiber optic cable or, in BASF’s case, directly
to the photo detector. BASF offers lightpipes in standard diameters of 2 mm,
3 mm, and 4 mm. Lengths are application specific, but generally range from a
few centimeters to 1 meter.
Maximum
Operating
Temperature
The maximum temperature at which an instrument or sensor can be safely
operated. A sapphire lightpipe can survive and measure temperatures up to
about 1,900°C, while a lens assembly can measure temperatures up to and
above 4,000°C. The electronics ambient operating range is 10°C to 60°C
.
Melting Point
The temperature at which a substance transforms from a solid phase to a
liquid phase. A high purity material melts at a known temperature and is often
used as reference point.
Micron
One millionth of a meter, 10
-6
meters, µm. Often used to describe the
wavelength of light that is being measured. The human eye can see from
about 0.38µm to 0.77µm.
EXACTUS
®
instruments typically measure at
longer wavelengths, from about 0.6µm to 2µm (also see
Wavelength
).
Noise
An unwanted electrical interference to the signal. Noise can be expressed in
terms of resolution (also see
Resolution
).
Photo Diode
Current
The electrical signal sent out by the photo diode. The smallest current the
EXACTUS
®
instrument can resolve is about 10
-15
amps, and the largest is
about 10
-3
amps, corresponding to the lowest and highest temperature
measurable respectively. Looking at currents is often helpful in sorting out
“true” emission from background light.
PID
Proportional, integral, derivative. A three-mode control action where the
controller has time proportioning, integral (auto reset) and derivative rate
action. Today there are more advanced control methods including adaptive
and model based control.
Planck,
Maxwell
Max Planck (1858–1947) was the physicist who first mathematically
described the light emitted from a blackbody using the novel idea of the
“Quanta”. Planck was a student of Gustav Kirchhoff and a friend and
colleague of Einstein. Planck received the Nobel Prize for Physics in 1918 for
his ground breaking “
Planck’s Radiation Equation
”.
