| OCR Text |
Show calibrated by determining the ratio measured when observing a black body. The calibration constant, a, is the ratio of the measured and the calculated values of R, respectively Rt,' and Rt" with E set to unity, so that: a = R., I Rt,'. The calibration allows for differences in bandwidth (AA), and for different proportionality constants between the - energy signal and the voltage response representing that signal. It does not allow for different (non-gray) emissivity variations with wavelength. However, for coal char particles, the best evidence as summarised previously [2,4] is that the particles are gray body, and that the emissivity ratio: (EAI I Eu) can be taken as unity. With the calibration constant thus detenninecL the temperature of the emitting source (particles) is then calculated from Eq. 1 using: T = C2.[(I/"-2) - (l/Al)] / In(a.R') [2] Derivation [3,2,4] of these equations requires specification of a radiating area since the signal received is the sum of the radiation from the particles and from the (cooler) spaces between the particles [3]. A value for the normalized area can then be calculated in principle, if the (gray body) particle emissivity is known, by comparing the signal from the flame and from the black body where the radiating area is unity. If the particle emissivity is not known, the relative fractional area radiating can still be obtained by nonnalizing the energy flux density against the mean value in a measured set· of values. This last is the procedure used in Ref. 2. 3. Selected Results. Typical results obtained are illustrated in Figs. 5, 6, and 7. As noted above, these have all been reported in relevant pUblications: they are reproduced here as illustration of the pyrometer operation, and to illustrate particular characteristics of the device. Figure 5, originally reported in Ref. 1, compares two color measurements with suction pyrometer measurements obtained in the large furnace. The furnace is a square section 5 |
