The model M395 blackbody source represents an unusual and highly innovative approach for the design of a truly universal blackbody source, which satisfies the most demanding requirements of modern radiometric calibration needs. This is indeed a milestone step, taken by Mikron Engineers, to satisfy seemingly two irreconcilable design criteria up to now, an ability to reach extreme high temperatures of 2300°C and at the same time to satisfy the need for near ambient temperatures. Due to the unique design of heated cavity shape, higher emissivity factor of near unity is achieved. This feature alone allows the calibration of the infrared instrument with wavelength range from 500nm to 20.0μm with much higher precision than previously possible. The flatness of spectral emissivity eliminates the constant awareness of potential errors associated with longer wavelength instruments under calibration. Due to incredible slew rate of near 300°C per minute and temperature resolution of 0.1°C, model M395 has the ability to replace number of existing blackbody sources with in an industrial facility or research laboratory with smaller foot print. It takes only several minutes to reach to any desired set points. Highly uniform emitter temperature further insures that infrared instruments with different field of view are equally
accurate during calibration.
Mikron has been designing and manufacturing blackbody sources since 1970. During the 1990's Mikron introduced 8 ultra-precision freezing point blackbody calibration sources as fixed point, primary calibration standards for the checking of transfer standards at discrete temperatures assignments from 29.76°C, the melting point of gallium, to 1084.62°C, the freezing point of copper. All the blackbody sources were compared with NIST equivalent blackbody sources and the temperature uncertainties were established. These precision instruments have been installed in several institutes responsible for maintaining radiance standards. During the last two years, Mikron has added additional high precision, but variable temperature, blackbody sources for producing ultra-accurate radiance standards. These new blackbody sources overcome the limitation of
freezing points that can produce only a single melt or freezing radiance standards. In all of the new blackbody sources very important criteria has been preserved. Flat and near flat unity of the emitter spectral emission response, the reconciliation of the measurement between radiometric and thermometric measurements to
achieve a high degree of precision and repeatability. The models, which will be introduced in this paper, are as follows: Model M300X, an ultra-precision blackbody source for temperature measurement from 50.00° to 1100.0°C; Model M350, a precision blackbody source, exclusively designed for calibration of wide incidence angle of heat
flux gauges, for temperatures of 300° to 1100°C corresponding to over 200KW/m2 of incidence radiance; and Model M345X12, an extended area blackbody source with Lambertian emitter and dimensions of 305X305 mm
for precision non-uniformity correction (NUC) and calibration of the wide-angle thermal imagers.
In refineries, thermal imaging has been used for many years to monitor the interior temperatures of furnaces, particularly the furnace wall-tubes, in the presence of combustion gas flames. The temperature range in these processes varies from 400 to 1200°C. Flame combustion byproducts contain gases of H<sub>2</sub>O, N<sub>2</sub>, CO<sub>2</sub>, NO and small residues of ashes and other particles that emit thermal radiation toward wall tubes resulting in heating of the tubes. Typically, a mid-infrared (MWIR) instrument is used, equipped with a narrow band-pass filter centered at 3.90μm. In this band there is a void in the emission spectrum of these gases making them transparent, and an instrument operating only in this band can provide very high quality thermal images of the furnace interior.
Operating temperatures at other points in petrochemical-related processes, closer to ambient temperature, can also be very critical. For example, a 10°C temperature difference from desired temperature at the coil output of a heat exchanger of a large ethylene plant can result in substantial revenue loss per year. Monitoring of these conditions is usually accomplished using a long wave infrared (LWIR) imaging radiometer operating in the 8-14μm spectral bands.
This paper will review the evolution of techniques for furnace wall-tube monitoring, discuss current techniques and conclude with the description of a modern dual-band approach. In this approach a single, portable uncooled thermal imager is deployed in a refinery to monitor both the status of high temperature elements such as wall tubes and the operating condition of the furnace and its ancillary equipment. Case histories with thermographic illustrations will be presented.
Infrared imaging, sensing and measuring devices and infrared lasers require predictable and accurate sources of infrared radiation as a basis for accurate calibration. This paper discusses the theory governing the design and construction of such devices (Blackbody Sources), and references the theoretical laws relating to infrared radiation, absorption and reflection.